volcanic ash impacts on critical infrastructure

Volcanic ash impacts on c

Thomas M. Wilson a,, Carol StewJim W. Cole a, Johnny Wardman a

aDepartment of Geological Sciences, University of Canteb Joint Centre for Disaster Research, Massey University acDepartment of Civil, Environmental and Geomatic Engi

a r t i c l e i n f o

Article history:Available online xxxx

Keywords:Volcanic riskElectricity suppliesWater suppliesWastewaterTransportTelecommunications

of interference from ash plume-generated lightning. However, some telecommunications equipment isvulnerable to airborne ash, in particular heating, ventilation and air-conditioning (HVAC) systems whichmay become blocked from ash ingestion leading to overheating.

Corresponding author. Tel.: +64 3 364 2987x45511; fax: +64 3 364 2967.E-mail addresses: [email protected] (T.M. Wilson), [email protected] (C. Stewart), [email protected] (V. Sword-Daniels),

[email protected] (G.S. Leonard), [email protected] (D.M. Johnston), [email protected] (J.W. Cole), [email protected] (J. Wardman),Barnard).

Physics and Chemistry of the Earth xxx (2011) xxxxxx

Contents lists available at ScienceDirect

Physics and Chemistry of the Earth

journal homepage: www.elsevier .com/locate /[email protected] (G. Wilson), [email protected] (S.T.tion to compensate for higher turbidity; managing water demand; and communicating monitoringresults with the public to allay fears of contamination. Ash can cause major damage to wastewater dis-posal systems. Ash deposited onto impervious surfaces such as roads and car parks is very easily washedinto storm drains, where it can form intractable masses and lead to long-term ooding problems. It canalso enter wastewater treatment plants (WWTPs), both through sewer lines and by direct fallout. Damageto modern WWTPs can run into millions of dollars. Ash falls reduce visibility creating hazards for groundtransportation. Dry ash is also readily remobilised by vehicle trafc and wind, and dry and wet ash depos-its will reduce traction on paved surfaces, including airport runways. Ash cleanup from road and airportsis commonly necessary, but the large volumes make it logistically challenging. Vehicles are vulnerable toash; it will clog lters and brake systems and abrade moving parts within engines. Lastly, modern tele-communications networks appear to be relatively resilient to volcanic ash fall. Signal attenuation andinterference during ash falls has not been reported in eruptions over the past 20 years, with the exception1474-7065/$ - see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.pce.2011.06.006

Please cite this article in press as: Wilson, Tj.pce.2011.06.006ritical infrastructure

art b, Victoria Sword-Daniels c, Graham S. Leonard b, David M. Johnston b,, Grant Wilson a, Scott T. Barnard a

rbury, Private Bag 4800, Christchurch 8140, New Zealandnd GNS Science, P.O. Box 756, Wellington, New Zealandneering, University College London, Gower Street, London WC1E 6BT, United Kingdom

a b s t r a c t

Volcanic eruptions can produce a wide range of hazards. Although phenomena such as pyroclastic owsand surges, sector collapses, lahars and ballistic blocks are the most destructive and dangerous, volcanicash is by far the most widely distributed eruption product. Although ash falls rarely endanger human lifedirectly, threats to public health and disruption to critical infrastructure services, aviation and primaryproduction can lead to signicant societal impacts. Even relatively small eruptions can cause widespreaddisruption, damage and economic loss.Volcanic eruptions are, in general, infrequent and somewhat exotic occurrences, and consequently in

many parts of the world, the management of critical infrastructure during volcanic crises can beimproved with greater knowledge of the likely impacts. This article presents an overview of volcanicash impacts on critical infrastructure, other than aviation and fuel supply, illustrated by ndings fromimpact assessment reconnaissance trips carried out to a wide range of locations worldwide by our inter-national research group and local collaborators. Critical infrastructure includes those assets, frequentlytaken for granted, which are essential for the functioning of a society and economy.Electricity networks are very vulnerable to disruption from volcanic ash falls. This is particularly the

case when ne ash is erupted because it has a greater tendency to adhere to line and substation insula-tors, where it can cause ashover (unintended electrical discharge) which can in turn cause widespreadand disruptive outages. Weather conditions are a major determinant of ashover risk. Dry ash is not con-ductive, and heavy rain will wash ash from insulators, but light rain/mist will mobilise readily-solublesalts on the surface of the ash grains and lower the ash layers resistivity. Wet ash is also heavier thandry ash, increasing the risk of line breakage or tower/pole collapse. Particular issues for water supplymanagers include: monitoring turbidity levels in raw water intakes, and if necessary increasing chlorina-ll rights reserved.

.M., et al. Volcanic ash impacts on critical infrastructure. J. Phys. Chem. Earth (2011), doi:10.1016/

This summary of volcanic ash impacts on critical infrastructure provides insight into the relative vul-nerability of infrastructure under a range of different ashfall scenarios. Identifying and quantifying theseimpacts is an essential step in building resilience within these critical systems. We have attempted toconsider interdependencies between sectors in a holistic way using systems thinking. As modern societybecomes increasingly complex and interdependent this approach is likely to become increasinglynecessary.

2011 Elsevier Ltd. All rights reserved.

1. Introduction

It has been estimated that nine percent of the worlds popula-tion lives within 100 km of a historically active volcano (Horwelland Baxter, 2006). This proportion is likely to continue to increasedue to higher-than-average rates of population growth in many re-gions and countries such as Central America, equatorial Africa,Colombia, Ecuador and the Philippines that are highly volcanicallyactive. Eruption frequencies for a range of volcanically-active coun-

consequently in many parts of the world, infrastructure managersmay not have devoted serious consideration to management of avolcanic crisis.

1.1. Research context and methods

Over the past 15 years our international research group hasaimed to undertake a sustained and systematic approach to volca-

et al

N

V

1181

Alaska, Kamchatka, Kuril Islands 1.1 713 115 5 months 100 yearsEcuador 13.8Canada, Lower 48 states USA 335.8Italy 59.9Colombia 44.4Mexico 107.7New Zealand 4.3Chile 16.8Nicaragua 5.7Peru 27.9

a 2008 World Population Data Sheet, Population Reb The Volcanic Explosivity Index (VEI) is a classica

2 T.M. Wilson et al. / Physics and Chemistry of the Earth xxx (2011) xxxxxx

Please cite this article in press as: Wilson, Tj.pce.2011.06.006188 31 2 years 5 months 102 years147 18 1 year 6 months 143 years242 21 5 years 215 years5134 15 6 years 6 months 304 years114 25 7 years 6 months 375 years189 17 11 months 394 years339 17 1 year 4 months 554 years130 10 1 year 2 months 806 years39 4 14 years 2 months 832 yearsPhillippines 90.5 133 11 1 year 4 months 59 YearsPapua New Guinea 6.5 191 23 8 months 81 yearstries are shown in Table 1.Volcanic eruptions can produce a wide range of hazards.

Although phenomena such as pyroclastic ows and surges, sectorcollapses, lahars and ballistic blocks are most destructive and dan-gerous (Hansell et al., 2006), volcanic ash fall is by far the mostwidely distributed eruption product. Volcanic ash can affect manypeople because of the large areas that can be covered by ash fall.Although ash falls rarely endanger human life directly, threats topublic health, disruption to critical infrastructure services (e.g.electricity and water supplies, transport routes, waste water andcommunications), aviation, buildings and primary production,can lead to signicant societal impacts (Horwell and Baxter,2006; Stewart et al., 2006). Even relatively small eruptions cancause widespread disruption, damage and economic loss. Forexample, the 1995/1996 eruptions of Ruapehu volcano in the cen-tral North Island of New Zealand were very small by geologicalstandards (VEI 3, refer to Table 1 for denition) but still coveredover 20,000 km2 of agricultural land with ash fall and caused sig-nicant disruption and damage to aviation, communication net-works, a hydro-electric power scheme, electricity transmissionlines, water supply networks, wastewater treatment plants, agri-culture and the tourism industry (Cronin et al., 1998; Johnstonet al., 2000). The total cost of the eruption was estimated to be,in 1995/1996 value, in excess of $NZ 130 million ($US 104 million).

However, volcanic eruptions which produce abundant ash are,in general, infrequent and somewhat exotic occurrences, and

Table 1Eruption frequencies for selected countries (after Jenkins et al. (in press) and Wilson

Selected countries Population (2008)a (million)

Indonesia 239.9Iceland 0.3Japan 127.7Guatemala 13.7ference Bureau.tion scheme for volcanic eruption

.M., et al. Volcanic ash impacnic impact assessment in the following areas:

Critical infrastructure: including electricity, water supplies,wastewater, land and air transport, telecommunications.

Ash cleanup and disposal. Primary industries, including agriculture. Emergency management.

Our group has utilised a research model of undertaking recon-naissance trips to areas impacted by volcanic eruptions worldwide,in conjunction with empirical, laboratory-based testing of criticalinfrastructure components. Trips have been undertaken to investi-gate the impact of the following eruptions: Ruapehu, New Zealand(1945, 1995/1996); Mt St Helens, USA (1980 eruption);Sakurajima, Japan (1980s to present); Pinatubo, Philippines(1991); Hudson, Chile (1991); Mt Spurr, Alaska (1992);Reventador, Ecuador (2002); Etna, Italy (2004); Tungurahua,Ecuador (19992000 and 2010); Merapi, Indonesia (2006);Chaitn, Chile (2008); Redoubt, Alaska (2009), Soufrire HillsVolcano, Montserrat (2010) and Pacaya, Guatemala (2010)(Johnston, 1997; Johnston et al., 2000; Durand et al., 2001; Wilsonet al., 2010a,b,c; Leonard et al., 2005; Barnard, 2004; Wilson et al.,2007; Stewart et al., 2009a; Sword-Daniels, 2010; Sword-Danielset al., in press; Wardman et al., in press).

Research methods for the eldwork included: eld observation,eld testing, meetings, and semi-structured interviews. Interna-tional eldtrips were carried out in partnership with local or

. (2010a)).

umber of eruptions Average eruption frequency

EIb03 VEI 47 VEI 03 VEI 47

170 28 6 months 15 years47 26 6 years 10 months 43 years92 71 7 months 44 years05 8 4 years 9 months 53 yearss, ranging from VEI 08, with VEI 0 the least explosive (Newhall and Self, 1982).

ts on critical infrastructure. J. Phys. Chem. Earth (2011), doi:10.1016/

national in-country bodies in volcanic monitoring and emergencymanagement. Meetings and interviews were carried out withinfrastructure managers and operations and maintenance staff ataffected facilities. The interviews followed several prompt ques-tions which were used to steer the conversation, and touched uponthe main topics of interest for research including: the general im-pacts of volcanic ash fall on the sector; actions taken in response toash fall; ash clean-up operations; emergency management plans;and interrelated power, water and access impacts on the sectors.Interviews were semi-structured in nature to allow for freer explo-ration and discussion around the various topics that were touchedupon in conversation.

Trips have been undertaken at varying intervals post-eruptionto capture immediate impacts as well as impacts which havemanifested over time. The focus has been on both understandingash fall impacts on individual system components and overallsystem functionality. We are also working towards developing pre-dictive capacity by relating characteristics of ash fall events (fallthickness, grain size distributions, engineering properties such asdensity and abrasiveness, and chemical characteristics of the ash,

Fig. 1. Volcanic ash particle. Note the cavities are the broken walls of vesicles.

t to have a very thin surface coating comprised of readily soluble sulphate and chloride

T.M. Wilson et al. / Physics and Chemistry of the Earth xxx (2011) xxxxxx 3Fig. 2. Processes occurring within volcanic plumes. Volcanic ash particles are though

salts, and more sparingly-soluble uoride compounds. These are thought to be formed following the condensation of acidic aerosols (H2SO4, HCl and HF) onto ash particles,followed by the dissolution of cations such as Ca2+ and Na+ from the mineral surface. Consequently, freshly-fallen ash can release soluble components into surface waters, andis both corrosive and conductive. Figure used with permission of GNS Science.

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacts on critical infrastructure. J. Phys. Chem. Earth (2011), doi:10.1016/j.pce.2011.06.006

ion

istin combination with environmental conditions) to the type andseverity of impacts.

The purpose of this article is to present an overview of volcanicash impacts on critical infrastructure, illustrated by recent dataobtained by our group. We dene critical infrastructure (some-times also referred to as lifelines) as assets that are essential forthe functioning of a society and economy. In a broad sense it in-cludes the following (Platt, 1991):

electricity generation, transmission and distribution; gas and oil production, transport and distribution; telecommunications; water supply (drinking water, waste water/sewage disposal,stormwater and drainage networks);

food production and distribution; heating (e.g. natural gas, fuel oil, district heating); transportation systems (road and rail networks, airports, ports,inland shipping).

1.2. Scope of the paper

In this paper we focus on the following critical infrastructure:electricity generation, transmission and distribution; water sup-ply; waste water; telecommunications; and transportation sys-tems (excluding aviation which is covered by Casadevall (1994)and Guffanti et al. (2010)). Impacts on other critical infrastructure,

Fig. 3. Schematic illustration of the fall-out of particles from an umbrella erupt

4 T.M. Wilson et al. / Physics and Chemincluding food production and fuel production, will be the focus offuture analysis. The topics of building damage caused by ash, andhealth hazards of ash have been recently and comprehensively ad-dressed by others (Spence et al., 2005; Horwell and Baxter, 2006)and are not considered in this paper. Similarly, social consequencesof volcanic ash falls are beyond the scope of this paper.

The systems and networks that make up the infrastructure ofsociety are often taken for granted, yet a disruption to any one ofthose systems can have consequences across other sectors. Hence,this article also addresses interdependence of critical infrastruc-ture from a systems thinking perspective.

1.3. Properties of volcanic ash

Volcanic ash is the material produced by explosive volcaniceruptions that is

Field observations suggest that where ash thicknesses are thesame, ner ash will cause greater problems than coarser ash. It

ystems following different volcanic eruptions since 1980.

mistry of the Earth xxx (2011) xxxxxx 5ash contamination; (2) controlled outages during ash cleaning; (3)line breakage due to ash loading; (4) abrasion and corrosion of ex-posed equipment; and (5) disruption of generation facilities (Nellisand Hedrix, 1980; Stember and Batiste, 1981; Sarkinen and Wiit-ala, 1981; Blong, 1984; Heiken et al., 1995; Wilson et al., 2009).

2.1. Insulator ashover and the resistivity of volcanic ash

Insulator ashover is the most common impact on electricalnetworks from volcanic ash fall, and is a problem across genera-tion, transmission and distribution components. An unintendedelectrical discharge around or across the surface of an insulatingmaterial is known as a ashover (Fig. 5). Flashovers can occurwhen insulating surfaces are coated with a substance that is con-ductive, such as volcanic ash. Fresh volcanic ash has a thin surfacecoating of soluble salts (see Section 1.3 and Fig. 2). When dry, ashtypically has a low conductivity (high resistivity) to electrical cur-

Fig. 4. Summary of volcanic ash impacts to electrical s

T.M. Wilson et al. / Physics and Cherent, but when wetted, the soluble salts on the surface are mobi-lised and lower the resistivity. Power outages may occur if theload on the circuit is sufcient to trip the circuit breaker.

Many factors inuence ashover potential from volcanic ashcontamination, including grain size, soluble salt content, ash fallthickness, shape and composition of exposed components, net-work congurations and weather conditions before, during andafter the event (Fig. 6 and Table 2; Johnston, 1997). Interactions be-tween variables increase the complexity and difculty of makingpredictions. Important variables are discussed further below.

The presence of moisture is generally required to initiate ash-over. There have been no observations of dry volcanic ash causingashover to electrical distribution networks. However, heavy rainand/or strong winds will remove ash from lines, insulators andother equipment. Weather conditions of light, misty rain(12 mm/h) are considered the most likely to initiate ashoverduring or after ash fall (Wilson et al., 2009). Moisture may alsobe derived from the eruption plume itself or if the eruption has oc-curred through a water source such as a crater lake.

Moisture is also an important factor in ash adherence to ex-posed surfaces. Dry ash generally tends to rest only on horizontalor gently sloping surfaces whereas wet ash will stick to all exposedsurfaces. In experiments on ash from the Mt. St. Helens eruption(Nellis and Hedrix, 1980), heavy rain washed 66% of depositedash from insulators whereas light rain removed little ash. Windsof 55 km/h removed 95% of dry ash.

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006Fig. 5. An example of a ashover (three faults) on a glass string insulator. Theinsulator has been coated with 3 mm of wet volcanic ash. Flashover occurred at40 kV (insulator string design voltage 40 kV).


l du

l. (2

roba

sh t

ine

ighowediow

istFig. 6. Factors affecting ashover potentia

Table 2Risk of line and substation insulator ashover following ash fall (based on Wilson et a

Risk factors P

Line voltage Ash moisture content A

F

33 kV (regionalnational) Wet MDry L

6 T.M. Wilson et al. / Physics and Chemhas greater adherence to surfaces, more easily penetrates electricalequipment, and a higher surface area giving a higher soluble saltload and thus electrical conductivity when moist (Wilson et al.,2009).

Insulator size, composition, condition and orientation of insula-tors also inuence ash-induced ashover potential. In general,smaller insulators will be more vulnerable to ashover becauseof the shorter distance for the current to travel. The risk of ash-over increases as the proportion of the surface covered by ash in-creases; Nellis and Hedrix (1980) demonstrated that insulationthat has 30% or more of its creepage distance (the shortest distanceon the surface of an insulating material between two conductiveelements) either clean or dry has a low probability of initiatinginsulator ashovers. Composition is also important; newer-styleepoxy insulators increase ash adherence compared to porcelainor glass insulators (Heiken et al., 1995). Finally, surfaces that are al-ready contaminated (e.g. by sea spray) are more vulnerable to ash-induced ashover.

2.2. Generation sites

General impacts of volcanic ash fall on generation sites can in-clude ashover in substation yards (see Section 2.3); ash penetra-tion into buildings which may damage sensitive machinery andelectronics; damage to heating, venting and HVAC systems (seeSection 8); and structure failure such as the collapse of long spanroofs in the event of heavy ash fall. Impacts specic to hydroelec-tric power stations are discussed below. Insufcient informationwas obtained about the impact to thermal power stations for cov-erage here.

2.2.1. Hydroelectric power stationsSuspension of ash in storage dams can lead to abrasion of tur-

bines. During the October 1995 Ruapehu eruption, 7.6 million

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006e to volcanic ash (from Johnston, 1997).

009)).

bility of failure

hickness < 5 mm Ash thickness > 5 mm

ash Coarse ash Fine ash Coarse ash

Low High MediumLow Low Low

um Low High MediumLow Low Low

ry of the Earth xxx (2011) xxxxxxcubic metres of coarse basaltic andesite ash was deposited intothe Tongariro river catchment, leading to high levels of suspendedsediment. This catchment feeds the Rangipo power station(120 MW), which has an intake to the underground headrace tun-nel 20 km from Ruapehu volcano. The ash was composed of vary-ing mixtures of volcanic glass, plagioclase, orthopyroxene andclinopyroxene; there were also minor components of lithic orcountry rock fragments and spheroids of elemental sulphur (Cro-nin et al., 1998). Management decided to continue generationthroughout the eruptive episode. However, during inspections inApril 1996 it was discovered that signicant wear had occurredto the two Francis turbines and all auxiliary components thathad been in contact with the suspended ash. Over a six month per-iod the components suffered the equivalent of 16 years abrasiondamage (Meredith, 2007).

In contrast, turbine damage did not appear to be a feature of theimpacts of the May 2008 eruption of Chaitn volcano, Chile (de-scribed in more detail in Section 6.4), on the 448-MW Futaleuf hy-dro dam, located approximately 90 km SE of the volcano in Chubutprovince, Argentina. A direct ash fall of between 50 and 100 mm ofne-grained rhyolitic ash was received at the hydro dam, althoughgreater thicknesses were received across the storage lake. Due tothe ne grain size and high pumice content of the ash, it remainedsuspended in the lake for over eight weeks, during which time thedam continued to generate electricity. During our visit in February2009, engineers reported that there had been no drop in generationefciency, suggesting that turbines had not been damaged by abra-sion. However, no inspection had been made. There were minorconcerns about abrasion or corrosion damage to the interior ofthe penstocks as these were made of softer metal.

The Fuataleuf dam did suffer other problems as a consequenceof the ash fall. The heavy ash falls blocked rain gauges in the damscatchment. This was a major safety concern for the dam as the ashfall occurred during the rainy season when high rainfall events


009

< 10

mistrcould lead to rapid lake rises. The management also developedstrict building entry/exit protocols to limit ash ingress into build-ings, particularly to avoid contamination in the powerhouse andcontrol rooms. This included taping plastic sheeting around win-dows, doors and HVAC ducts; installing sticky oor mats to collectash off footwear; and instigating double-door entry.

Cleaning up the dam site was a major task. Over 180 t of ashwas removed from the powerhouse roof and substation area(approximately 1500 m2). There were also difculties with accessto the site due to the poor visibility and traction problems causedby ash falls on roads.

2.3. Substations

An electrical substation is a subsidiary component of an electric-ity generation, transmission and distribution systemwhere voltageis transformed from high to low or the reverse using transformers.Transmission and/or distribution lines concentrate at a substation,creating a vulnerable network node. Substations generally have anarray of switching, protection and control equipment and one ormore transformers. Much of this carries live current and so is vul-nerable to ashover if sufcient ash accumulates. Experience fromthe 1980 Mt. St. Helens eruption showed that substation insulatorswere more susceptible to ashover than line insulators due to theirshape and often horizontal orientation (Nellis and Hedrix, 1980).Ash can also abrade and clog equipment such as circuit breakers,cooling ns and HVAC system lters. For these reasons, precaution-ary cleaning at substations is common after an ash fall.

At Futaleuf dam site, Argentina, during the 2008 Chaitn erup-tion (discussed in Section 2.2.1) electricity transmission was dis-rupted by ash accumulating on vertical transformer insulators inthe step-up substation which induced a signicant ashover fault.The substation connects the dam to the Chubut province powergrid, a 240 kV high-voltage transmission system. The fault oc-curred in early May following light misty rain (approx. 2 mm/h)which wetted the ash, but did not wash it off surfaces. Flashoversalso occurred on the 240 kV high-voltage Chubut transmissionlines. Following this major fault, the dam, substation and transmis-sion lines were cleaned every 10 days for several months as a pre-caution, due to ongoing light ash falls and wind-remobilised ash.The ash was difcult to remove even with a high pressure hose,

Table 3Risk of damage to towers, poles and lines following ash fall (based on Wilson et al., 2

Weather conditions Ash thickness

Fine ash

Towers and poles Wet LowmediumDry Low

Lines Wet Low-mediumDry Low

T.M. Wilson et al. / Physics and Cheas it had formed a cement. In some cases crews had to chip ashoff the insulators with a screwdriver.

The gravel ballast (substrate) in substation and electrical yardsis of known resistivity to provide a safe environment for substationworkers. The deposition of moistened ash on ballast could poten-tially reduce resistivity and increase the possibility of an electrocu-tion hazard. However, although this was identied as a potentialhazard following the 1980 eruption of Mt. St. Helens, we are una-ware of any recorded impacts.

2.4. Transmission and distribution lines

Transmission lines carry bulk electricity at high voltages(110 kV or above) to reduce the energy lost over long distance from

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006generation source to users (e.g. population centres). Power is usu-ally transmitted through overhead power lines using three phasealternating current (AC). Typically transmission lines are sup-ported by large pylons with large strings of insulators (normallyceramic, glass or polymer construction). When close to the users,the voltage is stepped down through a substation transformer,and lower voltage lines distribute electricity to users. These distri-bution lines are usually mounted on poles with smaller singleinsulators.

The main impact of volcanic ash fall on transmission and distri-bution lines is likely to be insulator ashover. Lines may also bedamaged by heavy ash falls onto overhanging tree branches, par-ticularly if weather conditions are also snowy (Fig. 4 and Table 3).

Experience from impacts of the 1980 eruption of Mt. St. Helensvolcano on electrical networks (Sarkinen and Wiitala, 1981) sug-gests that transmission networks are generally less vulnerable toash-induced ashover than distribution networks. Transmissionnetworks (110500 kV) were able to withstand ash falls of69 mm before serious ashovers occurred. However, on smallerdistribution networks (33 kV) and domestic supply voltages(400 V) which received the same thickness of ash, ashovers werea more common problem, leading to sustained power outages ofseveral hours or longer. This was thought to be due to the smallersurface areas of insulators on these systems (Section 2.1).

Problems were also experienced following the May 2008 erup-tion of Chaitn volcano, Chile. On a 68 km-long 33 kV distributionline feeding the Chilean town of Futaleuf, 1020% of insulatorsashed over following falls of ne rhyolitic ash of at least 50 mmand in some areas over 100 mm, between 2 and 6 May. Failureoccurred several days after the ash fall, following light rain during69 May. Subsequent heavy rain washed off most of the ash, butthe undersides of insulators remained contaminated because neash had adhered to all sides. All insulators along this section of linewere replaced as it was considered too laborious to assess eachinsulator. Impacts were compounded by heavy snowfalls in the re-gion on 18 May, which increased the loading on lines (with 6 mmdiameter lines becoming 20 mm tubes of snow and ash). Ash andsnow-laden branches collapsed onto lines, requiring a further20 km of lines and poles to be replaced.

In other areas that also received ash fall from this eruption, net-works were more resilient. In the town of Futaleuf, 75 km south-

).

0 mm Ash thickness > 100 mm

Coarse ash Fine ash Coarse ash

Low Mediumhigh LowLow Medium Low

Low High LowmediumLow Medium Low

y of the Earth xxx (2011) xxxxxx 7east of the volcano, there was no failure to domestic supply lines,despite over 100 mm of ash fall during May. In the town of Esquel,110 km to the east in Argentina, there was no failure to 33 kV,13.2 kV, 222 V, and three-phase 380 V networks, despite 50 mmof ash falling on the town throughout May 2008. There were sev-eral controlled cuts for cleaning ash from transformer insulators.

A key mitigation action following an ash fall is to clean or re-place ash-covered insulators. Following the 1995/1996 eruptionsof Ruapehu volcano, ashover problems that occurred on 110 kVlines following just 3 mm of ash fall prompted the network ownersto experiment with cleaning methods. Methods trialled includedwater-blasting (1500 psi), re hosing, dry wiping and using a knap-sack sprayer and cloth. The most effective method was found to bewater-blasting followed by dry wiping (Powermark, 1995).


water supplies (Stewart et al., 2009b). Firstly, volcanic ash can

are sourced from deep (100120 m) wells. While the water re-

istmained uncontaminated by the ash fall, problems were experi-enced with electric and wind-powered pumps used to extract thegroundwater. In the case of windmills, ne ash penetrated thebearings and caused them to seize up. Thus, while groundwater-fed systems are generally less vulnerable to ash fall, well-headpumping equipment can still be a point of vulnerability.

3.2. Water quality impacts

The surface reactivity of volcanic ash is high and a range of ionsphysically disrupt or damage water sources and components ofwater supply, treatment and distribution systems. Secondly, thedeposition of ash into surface waters can change its physical andchemical characteristics. And thirdly, following an ash fall, therecan be heavy demands placed on water resources for cleanup pur-poses, and shortages can result if this situation is not managed.

3.1. Physical damage to water supply systems

While proximal hazards (particularly pyroclastic ows, ballisticejecta and lahars) can be particularly destructive to components ofwater supply systems, volcanic ash can also cause damage and dis-ruption on a more widespread scale.

Ash can block water intakes. The 1945 eruption of Mt Ruapehu,New Zealand, deposited ash falls of several mm thickness acrossthe North Island, which caused problems for the water supply inthe town of Taumaranui. Ash suspended in the Whanganui River,from which the town draws its supply, blocked lters at the sup-plys intake structure, reducing pumping rates from 90,000 l/h to31,500 l/h (Johnston, 1997).

Airborne ash can damage components of water distribution sys-tems such as electrically-powered pumps, electrical switchboards,lters andmotors. A dome collapse event at Soufrire Hills volcano,Montserrat, in July 2003 caused widespread ash fall over the is-land. The ash clogged springs and caused corrosion damage to hy-drant boxes and valves, and power outages and surges damagedelectrical switch gear at a pump station. These problems werecompounded by the intermittent power supply from Montserratsnational grid which was commonly affected by volcanic ash in-duced ashover faults. However the electricity network has re-cently been upgraded to mitigate damage by using protectioncircuit boards, so that the system is compartmentalised and thearea with the fault can be switched off. Previously whole-islandoutages would occur, before these were in place (PAHO, 2003;Sword-Daniels, 2010).

A further example comes from the 1991 eruption of VolcnHudson, Chile (Wilson et al., 2010a, 2010b). This eruption causedwidespread and long-lasting impacts on primary production andrural communities in Chile and Santa Cruz province, Argentina(Inbar et al., 1995; Wilson et al., 2010a). Horticulture in the regionbordering Lago Buenos Aires/Lago General Carrera is heavilydependent on irrigation, primarily using open channel ood irriga-tion systems. Channels became clogged with ash, and had to belaboriously excavated by hand. Ongoing ash deposition from wind-storms, which remobilised the ash, posed problems for the opera-tion of irrigation systems for two to three years after the eruption.In the arid coastal zone of Santa Cruz province, farm water supplies3. Impacts on water supplies

There are three main ways in which volcanic ash falls can affect

8 T.M. Wilson et al. / Physics and Chemcan be released into surface waters upon contact (Delmelle et al.,2007). Over 55 soluble components have been reported in volcanicash leachates (Witham et al., 2005), with the anions Cl, SO24 and

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006F and the cations Ca2+, Na+ and Mg2+generally the most dominant.Stewart et al. (2006) have developed a model to predict ionic con-centration increases in waters receiving ash fall (in the absence ofenvironmental buffering). This model can be stated concisely asfollows:

Cwater CashTDA=Vwhere Cwater is the predicted concentration increase of a solublecomponent in the receiving water body in mg/l, Cash is the concen-tration of that component in the ash in mg/kg dry weight, T is thethickness of the ash fall in metres, D is the density of the ash inkg/l, A is the surface area of the water body receiving ash fall andV is the volume of the receiving water body in cubic metres. Theterm A/V can be thought of as the vulnerability of a particularwater body to aerial contamination as it describes the surface areaopen to deposition relative to the volume available for dilution.

3.2.1. FluorideWitham et al. (2005) has reviewed volcanic ash leachate compo-

sition and concluded that while a range of elements of health signif-icance are reported to occur in ash leachates, the principal toxicelement adsorbed on volcanic ash is uoride (F). Fluoride concen-trations exceeding guideline levels (a level of 1.5 mg/l is set by theWorldHealthOrganisation though there areminor variations in lev-els adopted by different countries) are associated with an increasedrisk of dental uorosis, and levels exceeding 10 mg/l can lead toskeletal uorosis. These are generally long term (chronic) exposurelimits and effects. These authors recommend that this element bespecically monitored in volcanic ash from future eruptions, partic-ularly for volcanoeswhich have a past history of high uoride levels,such as Hekla volcano in Iceland. However, only a restricted numberof volcanic systems worldwide are particularly uoride-rich, nota-bly in Iceland and Melanesia (Witham et al., 2005).

3.2.2. AcidicationAsh leachates are typically acidic due to the presence in volca-

nic plumes of the strong mineral acids H2SO4 (formed from the oxi-dation of SO2), HCl and HF, and consequently may acidify receivingwaters, although the majority of surface waters have sufcientalkalinity to buffer against signicant pH change. For example, fol-lowing the May 2008 eruption of Volcan Chaitn in Chile, leachatefrom ash deposited on the city of Esquel, Argentina, was acidic (pH4.76 for a 1:25 mixture of fresh ash:distilled water). However, in asurface canal used for the citys water supply, the pH remained atnormal levels of 7.8 despite receiving ash fall (Stewart et al.,2009a). Similarly, following the eruption of Mt. Spurr volcano,Alaska in 1992, although deposition of ash into surface waterscaused dramatic increases in turbidity levels at the raw water in-take of the Ship Creek water treatment facility (Section 3.2.3),the pH of the raw water did not vary from its normal range of7.57.6 over the same time period (Stewart et al., 2009b).

Roof-fed rainwater tanks are particularly vulnerable to changesin acidity as rainwater typically has a very low alkalinity. InVanuatu, acidication of drinking water supplies (largely rainwa-ter-fed and stored in tanks or cisterns) is a well-characterisedproblem (Cronin et al., 2003). However, it is attributed primarilyto rainout of sulphate aerosol (Cronin et al., 2003) arising fromactive or passive volcanic degassing rather than ash fall. Evenlow atmospheric concentrations of SO2 can strongly acidify waterdroplets because of the relatively high solubility and dissociationconstants for this compound (Stewart et al., 2009b).

3.2.3. Turbidity

ry of the Earth xxx (2011) xxxxxxVolcanic ash particles suspended in water increase the turbidity(measured in Nephelometric Turbidity Units, or NTU). This is a crit-ically-important parameter in drinking water treatment, and it is


mistrT.M. Wilson et al. / Physics and Chemonitored closely throughout the process. Suspended particles canprotect micro-organisms from the effects of disinfection of watersupplies, and can stimulate bacterial growth. Effective water treat-ment depends on the control of turbidity. The Anchorage WaterandWastewater Utility (AWWU), for example, maintains a nishedwater turbidity of 0.1 NTU (compared to the USEPAs maximum al-lowed level of 0.5 NTU) to reduce the risk of a pass-through of theinfectious protozoan parasite Cryptosporidium (AWWU, 1995).

Turbidity is managed primarily with the addition of chemicalocculants such as aluminium or ferric sulphate; these serve toaggregate suspended particles so that they settle to the bottom.This is commonly followed up with the addition of lime and sodaash as secondary coagulants and to regulate the acidity of nishedwater to a slightly alkaline state. Chlorine is typically added to thenished water for terminal disinfection; in the event of turbidityincursions chlorination can be increased to compensate for higherturbidity levels.

Following the eruption of Mt Spurr volcano, Alaska, on 18August 1992, turbidity levels in raw water at the Ship Creek treat-ment facility (one of the two main water sources for the city ofAnchorage) increased dramatically from normal levels of 0.50.6NTU to 45 NTU the morning after the eruption (Fig. 7). As therewas redundant production capacity in the wider system, theAWWU was able to be shut down this plant for a period of approx-imately 30 h on a precautionary basis. Despite the major changes inturbidity, few other changes in water quality were noted in the dai-ly operations log in response to the ash fall (Stewart et al., 2009b).

3.2.4. Other parametersApplying the predictive model (Section 3.2) to ash fall from the

1995/1996 eruptions of Mt Ruapehu, which was well-character-ised in terms of its leachate composition, yielded some useful

Fig. 7. Turbidity increases at Ship Creek water treatment facility following eruption of

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006y of the Earth xxx (2011) xxxxxx 9insights into other probable changes to water quality in responseto volcanic ash fall (Stewart et al., 2006; Johnston et al., 2004).Although fresh ash will release a range of soluble components intosurface waters upon contact, those most likely to exceed guidelinelevels are the metals iron (Fe), manganese (Mn) and aluminium(Al). These elements are not normally considered to pose healthrisks and thus are regulated by secondary, non-enforceable guide-lines aimed at protecting the potability of the water rather thanprimary standards for elements of health concern. Exceedencesof guideline values for Fe, Mn and Al may cause raw water sourcesto become undrinkable due to a bitter metallic taste and dark col-our. However, volcanic ash fall has a highly variable compositionwith respect to its soluble surface coating (Johnston et al., 2004;Witham et al., 2005) and therefore caution should be used inapplying conclusions from a particular event more widely.

3.2.5. Public concernDuring and after an eruption a high level of public concern and

anxiety about contamination of water supplies by volcanic ash iscommon (Johnston et al., 2000). A timely, well designed and trans-parent monitoring programme which is communicated clearly tothe public can be very effective in allaying concerns (Stewartet al., 2009a).

3.3. Water shortages

Following a volcanic ash fall, there can be heavy demandsplaced on water resources for cleanup purposes, and shortagescan result if this situation is not managed. This can compromisekey services such as reghting capacity, and can lead to a lackof water for hygiene, sanitation and drinking.

Mt. Spurr volcano (data from Anchorage Water and Wastewater Utility, AWWU).


e cit

istFig. 8. Water demand and production for th

10 T.M. Wilson et al. / Physics and ChemThe 1992 eruption of Mt. Spurr volcano in Alaska and its effectson the city of Anchorage presents a well-documented case studyincluding daily operation logs from the citys public utilities(Johnston, 1997). The eruption of Mt. Spurr on 18 August 1992deposited about 3 mm of ne sand-sized volcanic ash on the city,120 km to the east. By 10 am the following day, the AWWU wasrecording a peak water demand rate of approximately 63 milliongallons per day (Fig. 8), a 70% increase over normal peak demands.The total daily demand for 19 August was 57 million gallons com-pared to the normal daily demand of 25 million gallons.

At 4 pm on 19 August, the Ship Creek water treatment facilityclosed down due to rapidly rising turbidity levels (Fig. 7). However,there was still adequate production capacity to meet peak demandfrom the other main water treatment facility (Eklutna) plus a wellsystem (consisting of 17 deep wells) that normally serves as astandby source. While the city did have adequate productioncapacity to meet the peak demand, bottlenecks existed throughoutthe distribution system and as a result, severe water shortages andloss of pressure occurred right across the city. Levels in severalstorage reservoirs dropped to dangerously low levels, and AWWUofcials were very worried that if building res had occurred dur-ing this period, it was unlikely that water for reghting wouldhave been available, particularly in the south and west of the city.The volcanic crisis gave the impetus to complete a major upgradeof the citys water transmission network.

4. Impacts on wastewater and stormwater networks

Volcanic ash fall can cause damage and disruption to wastewa-ter systems (both sewage and stormwater). Ash can enter andblock pipes and sumps, can cause accelerated wear on motorsand pumps, and can cause serious damage to wastewater treat-ment plants (WWTPs).

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006y of Anchorage, Alaska (data from AWWU).

ry of the Earth xxx (2011) xxxxxx4.1. Impacts on sewerage and stormwater drainage networks

When volcanic ash falls on impervious surfaces such as roads,car parks or roofs, even if only several millimetres thick, it can eas-ily be washed into stormwater drains by rainfall, or if water is usedfor cleanup operations. While stormwater sometimes has its ownseparate reticulation network, channelling runoff into naturaldrainages, there is commonly a degree of overlap with seweragereticulation systems, particularly for older infrastructure. Even ifsystems are separate, ash can still enter sewer lines by the pro-cesses of inow and inltration (e.g. through illegal connectionssuch as roof downpipes connected directly to sewer lines, crossconnections, ingress through household gully traps, around man-hole covers, or through holes or cracks in pipework).

Once ash has entered underground drainage networks, it canform unpumpable masses and be extremely difcult to remove.Consequences can include the failure of equipment such aspumps, and surface ooding. Following the May 27, 2010 erup-tion of Volcn Pacaya, Guatemala, between 30 and 100 mm ofcoarse (sand-sized) basaltic ash was deposited across much ofGuatemala City, located approximately 30 km to the north. De-spite a prompt and comprehensive cleanup operation organisedby the citys municipality, heavy rains caused by tropical stormAgatha shortly afterwards washed quantities of ash into the citysstorm drains where it caused widespread ooding problems(Fig. 9). One of the citys two main hospitals (Hospital Roosevelt)is located in an area with pre-existing drainage problems. Thehospitals basements ooded due to drains being blocked, andservices in this area had to be relocated. Guatemala City contin-ues to experience severe ooding problems during heavy rains,with motorway tunnels being particularly prone to ooding(Wardman et al., in press). These oods, in turn, lead to severedisruptions to trafc ow.


in silicic eruptions) will oat. Any residual ne ash persisting fur-

aircraft, railways, and ports and shipping. Additionally, during a

as vehicle headlights and brake lights are barely visible to other

mistrther through the treatment system may reduce the transmissivityof the efuent, which could compromise the effectiveness ofdisinfection.

On 18 May 1980, Mt. St. Helens volcano erupted and the city ofYakima (population 50,000), located 140 km to the east, receivedabout 10 mm of sand-sized ash. By the next day, about 15 times4.2. Impacts on wastewater treatment plants

Ash can enter WWTPs both via sewer lines (particularly if theseare combined with stormwater lines), and by falling directly ontreatment facilities.

4.2.1. Ash ingress via sewer linesAsh-laden sewage that enters a treatment plant may overload

equipment and lters designed to trap solid debris at both thepre-treatment and primary treatment stages. In particular,mechanical pre-screening equipment (such as step, rotating orbar screens) is particularly vulnerable to damage. Ash can abrademoving parts and block screens which can cause motors to burnout. Ash that enters primary treatment (sedimentation) tanks islikely to settle and thus increase the volume of raw sludge. Finergrain sizes may not settle and any pumice fragments (more likely

Fig. 9. Cleanup of Guatemala City roading network (photo credit: Ing. Alvaro HugoRodas Martini, Municipality of Guatemala City, 2010).T.M. Wilson et al. / Physics and Chethe normal amount of solid matter was being removed from thepre-treatment processes at Yakimas WWTP. This was despiteYakima having just ve percent combined stormwater and sewagelines. Ash was also observed in the raw sludge in the primary clar-iers. Throughout the day, it was evident that the facility was suf-fering damage as vibrations were occurring in the grit classier andthe gear box of the mechanically-cleaned bar screen. Pumping dif-culties were experienced and sludge lines became blocked. By thethird day, the passage of ash through the plant had stripped lterbeds bare and the comminutor failed (Day and Fisher, 1980).

On 21 May, the City Manager announced a decision to bypassthe treatment plant and discharge sewage (after chlorination) di-rectly to the Yakima River. The total damage to the treatment plantwas estimated to be US$4 million (1980 value; Day and Fisher,1980).

4.2.2. Direct ash fallAsh fall can be directly deposited on WWTPs and uncovered

equipment, such as open air biological reactors, ponds and clari-ers, is particularly vulnerable. More generally, airborne ash canclog air ltration systems, cause abrasional damage to movingparts of motors and cause arcing and ashover damage to electrical

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006drivers. After an ash fall, fast-moving vehicles will stir up ash alongroads creating billowing ash clouds up to tens of meters high cre-ating ongoing visibility hazards. The deposition of ne, hard ashparticles on road surfaces may reduce traction, particularly whenthe ash becomes wet. Ash deposits thicker than 1 mm will obscureor cover markings on roads that identify lanes, road shoulders,direction of travel, and instructions (for example, stop or slow)which may confuse and disorient drivers (Durand et al., 2001). Railtransportation is less vulnerable to volcanic ash than roads andhighways, with disruptions mainly caused by poor visibility andbreathing problems for train crews. Moving trains will also stirup fallen ash, which can affect residents living near railway tracks(Johnston, 1997).

Hard, ne-grained, abrasive and potentially corrosive ash can behighly damaging to vehicles. Fine-grained ash can inltrate nearlyevery opening and abrade or scratch most surfaces, especially be-tween moving parts of vehicles. Ash will block air and oil lters,thicken engine oil, and abrade seals and moving parts. Seals onhydraulic components may wear out faster than usual, and brakesand brake assemblies are especially vulnerable to abrasion andclogging from ash. Vehicles subjected to heavy ash exposure, suchas those used for cleanup operations, may require frequent brake,lter and greasing maintenance, as seen following the 2008Chaiten eruption. Ash caught between windshields and wipervolcanic crisis they may also be relied upon for the evacuation ofcommunities exposed to volcanic hazards.

5.1. Ground transport networks

Falling ash will signicantly reduce visibility, in some instancesto near total darkness. Safe driving becomes difcult or impossibleequipment. Heavier ash falls (>150 mm) may collapse long spanroofs.

The May 2010 eruption of Pacaya volcano (Section 4.1) hadwidespread impacts on Guatemala Citys wastewater treatmentfacilities. The city has hundreds of WWTPs ranging in size fromthose serving just a few households to larger facilities such asthe plant serving the University of San Carlos. This system utilisesan Imhoff tank (a combined sedimentation and sludge digestiontank). The Imhoff tank was lled with basaltic ash to a depth of45 m, both from direct ash fall and by washing in through sewerlines. Ash was reportedly very dense; the companys ownmeasure-ments indicate a density of 2.45 kg/l, which is in the range reportedfor the density of individual particles (2.353.3 kg/l, from Shipleyand Sarna-Wojcicki, 1982). As a result, the ash mixed with the sew-age sludge and sank to the bottom, where it was very difcult tomove. Sludge pumps were used to remove the lighter material,but the heavier ash-contaminated sludge had to be dug out withshovels. Wastewater maintenance contractors Mapreco reportedthat cleaning ponds and tanks typically took two to three days withsome systems taking a week to clean out. A further problem wasthat sludge pump propellers abraded, and their normal lifetimeof two years was reduced to 15 days (Wardman et al., in press).The company estimated that additional business caused by theeruption increased their prots by 20%.

5. Impacts on transportation networks

Ash fall may severely disrupt transportation systems over largeareas for hours to days, including roads and vehicles, airports and

y of the Earth xxx (2011) xxxxxx 11blades will scratch and permanently mark the windshield glass,and windows are susceptible to scratching each time they areraised, lowered, and cleaned. Corrosion of paintwork and exterior


istttings may also result where ash is in contact with the exterior(Johnston, 1997).

The disruption of transportation networks can have cascadingimpacts for other critical infrastructure sectors impacted by ashfall. Maintenance crews attempting to access impacted sites maybe disrupted or blocked entirely from accessing the site. Forexample during the Chaitn eruption shift workers were severelydisrupted accessing the Futaleuf hydroelectric power dam locatedapproximately 90 km SE of Chaitn volcano in Chubut province,Argentina. Thick falling ne-grained rhyolitic ash reduced visibilityto nil. The ash mixed with surface water on the roads and signi-cantly reduced traction, causing several minor accidents. Thesedangers, and the desire to reduce remobilization of ash aroundthe dam site by vehicle trafc, led to management deciding tomaintain operations with a permanent skeleton crew for a periodof one month, rather than rotating shifts.

5.1.1. Cleanup and disposalThe fall of a few millimetres of volcanic ash may result in the

need for disposal of large quantities of material from road net-works. Ash disposal should be undertaken in ways that minimisesongoing public health problems and is cost-effective (Johnstonet al., 2001). The time required to clean up ash deposits will de-pend on the extent and depth of ash deposits and may take fromseveral weeks to several months. Best results are achieved with acoordinated effort, where other agencies, utility companies andresidents clean ash from all areas at the same time, which mini-mizes continued contamination from remobilized ash. Ash shouldbe disposed of in a dedicated ash dump, rather than inlling valu-able landll space (see Johnston et al. 2001 for more information).

On 27 and 28 May, 2010, Guatemala City, received between 20and 100 mm of coarse (sand-sized) basaltic ash fall from an erup-tion of Pacaya volcano located approximately 30 km SSW (Ward-man et al., in press). Approximately 1 million people live withinthe city and 2.9 million live in the greater metropolitan area. Thesouth of the city was more severely affected than the north. Asthe city generates 70% of Guatemalas GNP, there was a strongmotivation to initiate a prompt and efcient city-wide cleanup toenable critical transport lifelines to be restored as quickly as possi-ble (Wardman et al., in press). The total quantity of ash depositedon the city was estimated to be 11,350,000 m3, and 2100 km ofroads required cleaning. The cleanup was organised by the Munic-ipality, and all available staff were co-opted along with assistancefrom the Army (Fig. 9). Factors contributing to the efciency of thecleanup were: the pre-existence of an earthquake emergency planwhich enabled heavy machinery to be mobilised quickly; a goodcommand structure; clear communication to the public (who wereasked to clear ash from their own roofs and yards, to be left at des-ignated collection points or picked up from the roadside); and thedonation of a large number of bags from sugar and cement compa-nies for ash collection. Costs of heavy machinery hire (trucks, exca-vators and Bobcats) were estimated at Q1.6 million (US$ 0.2million in September 2010). Few problems were reported withash being remobilised, or causing additional wear and tear onmachinery. This was probably due both to the coarse and densenature of the ash, and also that the city experienced heavy rainsshortly after the eruption due to tropical storm Agatha. Quantitiesof ash were washed into storm drains where it has caused ongoingooding problems (Section 4.1).

5.1.2. Potential re-useVolcanic ash can be used for a range of purposes, from building

aggregate to landscaping ll. Ash is mined from pyroclastic density

12 T.M. Wilson et al. / Physics and Chemcurrent deposits at Merapi volcano, Indonesia, and lahar depositsfrom the 1991 Pinatubo eruption, Philippines, as a valuable build-ing aggregate for cinder block construction. Following the 1973

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006eruption of Eldfell, Iceland, the coarse volcanic ash and lapilliwas a valuable source of ll on the island of Heimaey and usedfor inlling valleys for new urban development.

However in the case of the 27 May, 2010 eruption of Pacaya vol-cano, testing conducted on the ash deposited on Guatemala Cityindicated it was unsuitable for use as aggregate due to its friability(low mechanical strength).

5.2. Airports

An authoritative recent review by Guffanti et al. (2009) of volca-nic hazards to airports found that between 1945 and 2006, 101 air-ports in 28 countries were affected on 171 occasions by eruptionsat 46 volcanoes. These authors conclude that these hazards are notrare on a worldwide basis, as since 1980, ve airports per year onaverage have been affected by volcanic activity. The main hazard toairports is ash fall, with accumulations of only millimetres is suf-cient to force temporary closures of some airports. A substantialportion of incidents has been caused by ash in airspace in the vicin-ity of airports, without accumulation of ash on the ground. Thiswas dramatically exhibited by the Eyjafjallajkull eruption inAprilMay 2010 which caused widespread airport closures in theUK, European and North Atlantic airspace. There were closuresfor six consecutive days in April 2010 and further disruptionsand closures into May as air trafc controllers and airlines followedthe ICAO rule of zero ash tolerance. Research following this crisishas served to better inform ash concentration tolerances for jet tur-bines (Gislason et al., 2011; Drexler et al., 2011). By 21 April,95,000 ights had been cancelled in European airspace causinglarge economic losses to airline companies, the insurance industryand many industries dependent on gaining access to Europeanmarkets (Sammonds et al., 2010). In contrast, long term experienceat Anchorage airport, Alaska, has led management to close the air-port only when ash falls on the runway.

On a few occasions, airports have been impacted by hazardsother than ash (pyroclastic ow, lava ow, gas emission, and phre-atic explosion). A consideration of ash impacts on airborne aircraftis beyond the scope of this paper. Refer to Casadevall (1994) andGuffanti et al. (2010) for further information on this topic.

5.2.1. Case study: Guatemala CityGuatemala Citys international airport (La Aurora) received its

rst warning of impending ash fall at 6:30 pm on 27 May, 2010.The airport was ofcially closed at 7:23 pm the same evening,and re-opened at 1:18 pm on 1 June (Airport Manager, DireccionGeneral de Aeronautica Civil). Approximately 2030 mm of coarse(sand-sized) basaltic ash fell on La Aurora airport. The main reasonfor the airport closure was to allow for cleanup of the airport,rather than because of airborne ash hazards to aircraft. The person-nel requirements for the cleanup were 30 staff from DGAC plus anadditional 500 staff loaned by the army and air force. A stagedcleanup of the runway and apron involved rstly using bulldozersto scrape ash into piles, where it was then shovelled into trucksboth manually and using Bobcat loaders, followed by cleaning withstreet sweepers and nally cleaning with compressed air. The newbituminous runway surface (which cost $1.7 million USD inDecember 2009) was destroyed by abrasion damage. Markingson the runway and apron were also severely damaged by abrasionand had to be completely repainted before the airport could re-open. An estimated 56,000 m3 of ash was removed from the run-way and apron. Costs of the airport closure were estimated to be$250,000 USD (2010) in loss of income to businesses based at theairport. The airport buildings were also damaged by the ash fall.

ry of the Earth xxx (2011) xxxxxxGutters and downpipes were clogged with ash and caused leaksin the ceiling which were continuing some four months later,and the paint coating on the roof suffered abrasion damage.


Volcano Disaster Assistance Programme, pers. comm., 2010).

(mentioned in Section 6.1) associated with ash plumes may also

mistrHowever the phenomenon is not well documented in othereruptions. There have been numerous examples of telecommuni-cations transmissions continuing to work during volcanic ash falls(Section 6.4). A recent analysis by telecommunications engineersfor the New Zealand-based Auckland Engineering Lifelines Groupconcluded theoretically that impacts on electromagnetic signaltransmissions would probably be limited to low frequency servicessuch as satellite communications (Wilson et al., 2009). Interference(such as static) to signal transmission may also be caused by light-ning, as lightning is frequently generated within volcanic ashplumes (McNutt and Williams, 2010).

6.2. Ash damage to equipment

Direct damage to network components (such as electronics) hasbeen observed during several eruptions. Modern telecommunica-tion systems require constant cooling for their electronics. Disrup-tion of these HVAC systems can occur either by air-intake blockageor by precautionary shut-down to avoid problems (Johnston,1997). The vulnerability of HVAC systems is described further in5.3. Marine transportation

Marine transportation can be affected by volcanic ash in threemain ways: direct physical impacts from falling ash, visibility dis-ruption and physical impacts from pumice rafts. Similar to groundtransportation, volcanic ash may clog air intake lters and abrademoving parts if ingested into engines. Thick ash falls will also re-duce visibility creating a hazard to navigation. The third impactis unique to marine transport. Vesiculated ash (pumice and scoria)will oat on the surface of water bodies in pumice rafts. Theserafts can clog salt water intake strainers very quickly, which can re-sult in overheating of shipboard machinery dependent on seawater service cooling.

The 2008 Chaitn eruption in Chile prompted mass evacuations,which were largely carried out by marine transport. Small out-board motors were reportedly severely abraded and exhaust andcooling vents clogged by the oating pumice in Chaitn harbour.Larger vessels also suffered problems when oating ash pumicewas sucked into the salt water service system, clogging sea strain-ers and leading to engine overheating.

6. Impacts on telecommunication networks

Impacts of volcanic ash on telecommunication and broadcastingnetworks include: (1) attenuation and reduction of broadcast sig-nal strength; (2) ash damage to equipment; (3) indirect impacts,including overloading of networks through high user demand.

6.1. Signal attenuation and interference

It has been recorded that telecommunications signals have beendisrupted during volcanic eruptions, notably following the 1969Surtsey eruption and 1991 Pinatubo eruption. Scientists respond-ing to the 1991 Pinatubo eruption in the Philippines reportedVHF (160175 MHz) telemetry was interrupted on 15 June whenco-ignimbrite ash rose into the line of sight of seismic data trans-missions (typically received at powers 3040 dB above squelch,1 lV). This may have been due to the large concentration ofcharged particles within volcanic plumes causing signal attenua-tion. The team had uninterrupted communications via a commer-cial cell phone network (J. Ewert and A. Lockhart, USGS/OFDA

T.M. Wilson et al. / Physics and CheSection 7.2. Transmitting equipment, such as antennas and radiomasts, may experience ashover when contaminated with moistash (Wilson et al., 2009). Abrasion, clogging and corrosion damage

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006damage telecommunications equipment. Following the August1991 eruption of Volcn Hudson, Chile, HF and VHF radio receivermasts within 80 km of the volcano were struck by lightning, whichdestroyed the systems and affected the operation of the radio tele-phone system in the region (Wilson et al., 2010c).

6.3. Network overloading

Observations and reports from recent eruptions suggest that thelargest single communications disruption is network overloadingdue to high user or data demands during an ash fall (Wilsonet al., 2009). This is a common feature of many natural disasters.

6.4. Case study: May 2008 eruption of Chaitn volcano, Chile

After more than 9000 years of inactivity, Chaitn volcano, Chile,began erupting on 2 May 2008 with emissions of ash to an altitudeof 20 km. On 6 May, the eruption intensity increased markedlywith the eruption column reaching 30 km. This was the largestevent worldwide since the eruptions of Pinatubo and Hudson vol-canoes in 1991. Experiences from this event provide a useful casestudy of the performance of telecommunications networks duringa major eruption. Our team visited the affected areas during Janu-ary/February 2009.

In general, telecommunications networks were highly resilientto ash fall impacts, even though signicant ash falls were receivedin towns such as Futaleuf (initial ash fall of 30 mm, total ash fallduring May of approximately 150 mm). There were no reports ofinterruptions to service within the zone that received ash fall. InFutaleuf, emergency management staff reported that cellularand satellite phones, UHF radio and telemetered sites all continuedto broadcast and receive signals throughout the eruption. Satellitedishes did experience some problems due to ash accumulation butthis was easily mitigated by regular cleaning or covering disheswith a thin membrane. The only notable problem for cellular andlandline networks was overloading due to high user demand.

The ne rhyolitic ash did cause damage to equipment. Cellularphones stopped working when ash penetrated their interiors andpossibly short-circuited electronics or clogged keys. Video and stillcameras also stopped working in the ashy conditions. However, ifgently cleaned with compressed air or nitrogen and wiped with adamp cloth most reportedly resumed working. There were no re-ports of exchanges or transmitters suffering damage from ashingestion.

7. Impacts on critical components

This section describes impacts on components which are com-mon to most critical infrastructure sectors, and on which theymay be heavily reliant.

7.1. HVACto mechanical switches has also been reported (FEMA, 1984),although with the trend towards solid state electronics, this isarguably a reducing vulnerability.

Heavy ash falls may cause lines, cables, masts, aerials, antennae,dishes and towers to collapse due to ash loadings or the collapse ofoverhanging branches. Long-term exposure (weeks to months) ofsensitive equipment to airborne ash can also lead to acceleratedcorrosion (Wilson et al., 2009; Barnard, 2009). Lightning strikes

y of the Earth xxx (2011) xxxxxx 13Heating, ventilation and air conditioning (HVAC) allows envi-ronmental control within structures. They are an essential andwidespread part of critical infrastructure. They are essential for a


applications.

preventing ashy eld clothes from being worn in operating rooms.

isthealthy working environment inside inhabited buildings and formaintaining critical components of infrastructure in working or-der. In particular, HVAC systems are a critical component of muchmodern infrastructure. Most electronic control systems cannotfunction without external cooling, due to the heat generated byinternal computers. For example, nearly all telecommunication ex-change and cell sites require constant air conditioning. Other sys-tems dependent on HVAC include medicine stores in hospitalsand storage facilities for perishable food. Large commercial or pub-lic buildings also require interior temperatures to be controlled, sorequire large HVAC systems.

Air conditioners are known to be vulnerable to ash blockage,corrosion and arcing of electrical components, and air-lter block-age, especially if air intakes are horizontal surfaces. The type ofHVAC system varies greatly depending on requirements. Sealedstructures using an internal HVAC system (with external con-denser) are less at risk than structures relying on external freshair intakes, which blow ash directly onto electronics or lters canbecome blocked. Air lters used at communications sites are typi-cally not designed to cope with the volume of material seen in anash fall.

Following the 1992 eruption of Mt Spurr volcano, Alaska, HVACintakes in the Anchorage telephone exchange experienced block-ages, resulting in all air handling units being manually shut downafter an ash fall of approximately 3 mm thickness. Fortunately, thecool temperatures in Anchorage were sufcient to prevent ex-changes overheating, so shutdowns were not necessary (Johnston,1997). Shutdowns of air handling units were on a precautionarybasis.

During the 1995/1996 eruptions of Ruapehu volcano, ash fallswere widespread over the North Island of New Zealand. InRuatoria, 280 km distant, high temperature alarms in a small road-side exchange cabinet were triggered after air-conditioning lterswere clogged with ash, following 12 mm of ash fall in this area(Johnston, 1997).

There have also been many instances of HVAC systems showingresilience to airborne ash. The city of Kagoshima, Japan, has re-ceived frequent light ash falls (

mo

mistrcan have positive or negative effects. A broad approach must be ta-ken to understand the dependency between systems and how anysolution to the problemmay have consequences for the rest of thesystem. The aim of this approach is to pre-empt any cascadingproblems, and achieve overall improvement in systemperformance.

The cascading effects to other sectors constitute the dynamicvulnerability of the system and its environment. For example,ash-blocked drains can cause secondary ooding that may recurfor weeks or months following an eruption, until the system iscleared of ash. The secondary ooding can cause road access prob-lems, and can prevent access to impacted infrastructure for main-tenance or repair. In this way the ash fall impacts on the waterinfrastructure system can have a knock-on effect to the functional-ity of transport systems. Equally the external context or environ-ment can affect any particular system. For example infrastructuremanagement protocols may be dependent on communications sys-tems that can become overwhelmed and inoperable during crises,as a result of high user demand.

Both direct and indirect effects contribute to any systems vul-

Fig. 10. An inputoutputT.M. Wilson et al. / Physics and Chenerability. Using a systems thinking approach to physical vulnera-bility, the internal and external inuences on a system and theirinterdependencies, as well as the cascading impacts on other sec-tors beyond the system boundaries are taken into account. Disrup-tions may have a feedback mechanism to the original system,resulting in secondary impacts on a sub-system facility and long-er-term disruptions or delayed recovery.

8.2. Case study in infrastructure interdependency: Montserrat

In order to demonstrate the intricate relationships and interde-pendencies between critical infrastructure sectors, we present acase study from Montserrat. Since 1995 the Soufrire Hills volcanohas been in eruption causing dramatic impacts to the small Carib-bean island of Montserrat. Pyroclastic density currents and subse-quent lahars have devastated much of the southern part of theisland. In addition, intermittent ash falls have caused a range of im-pacts to critical infrastructure in the inhabited regions to the north.A study in early 2010 investigated ash impacts on critical infra-structure and their interdependencies (Sword-Daniels, 2010).

The study found that electrical power failures by ash contami-nation of insulators causing ashovers had signicant knock-on(cascading) effects. These included power surges when the powerwas restored and subsequent failure of electrical appliances, as

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006well as impacts to critical infrastructure system functionality, com-munications networks, and HVAC units. Financial costs associatedwith this disruption include replacing appliances, business inter-ruption costs, repair work on the electrical system, and the costof regular maintenance.

The relative importance of the infrastructure in question mustalso be thoroughly understood in order to address the real prob-lems that are caused by volcanic ash fall. Importance and interde-pendency are intricately linked; where complex secondary ortertiary impacts may lead to heightened system stress, in compar-ison with the primary impact alone. This is highlighted in Montser-rat, where power failures are perceived to be a minor nuisance bythe local population (where disruption is only for a few hours, onceor twice a month). However, the functionality of HVAC depends onpower. HVAC allows for comfort in tropical climates, but it alsoprevents critical (and expensive) computer systems from overheat-ing and helps to mitigate ash ingress into buildings. Continuouspower supply is therefore critical to preserving the longevity ofcomputer systems and electrical equipment and reducing interiorcorrosion.

The cumulative effect of ash fall impacts highlights the impor-

del for systems thinking.y of the Earth xxx (2011) xxxxxx 15tance of a holistic approach. Research on interdependent impactsand across disciplines is more likely to develop practicable assess-ment methodologies and adaptation or mitigation solutions, foruse by practitioners such as utility providers, infrastructure engi-neers, system architects and emergency managers.

9. Discussion and conclusions

This paper has summarised ash impacts on critical infrastruc-ture, identied key points of vulnerability and compared the rela-tive vulnerability of different sectors under a range of different ashfall scenarios. Understanding these vulnerabilities is an essentialrst step to build resilience into infrastructure systems.

9.1. Summary of impacts by sector

Electricity networks are very vulnerable to disruption from vol-canic ash falls. This is particularly the case for ne ash because ithas a greater tendency to adhere to line and substation insulators,where it can cause ashover (unintended electrical discharge)which can in turn cause widespread and disruptive outages.However, weather conditions are a major determinant of ashoverrisk. Dry ash is not conductive, and heavy rains will wash ash from


istinsulators; but light wet weather conditions will mobilise readily-soluble salts on the surface of the ash and lower its resistivity. Wetash is also heavier than dry ash, increasing the risk of line breakageor tower/pole collapse.

Particular issues for water supply managers are likely to bemonitoring turbidity levels in raw water intakes and if necessaryincreasing chlorination to compensate for higher turbidity; manag-ing water demand; and communicating monitoring results withthe public to allay fears of contamination.

Ash can also cause major damage to wastewater disposal sys-tems. Ash deposited onto impervious surfaces such as roads andcar parks is very easily washed into storm drains, where it can formintractable masses and lead to long-term ooding problems. It canalso enter wastewater treatment plants, both through sewer linesand by direct fallout. Damage to modern WWTPs can run into mil-lions of dollars.

Ash falls reduce visibility creating hazards for ground transpor-tation. Dry ash is also readily remobilised by vehicle trafc andwind. Dry and wet ash deposits will reduce traction on paved sur-faces, including airport runways. Ash cleanup from roads and air-ports is commonly necessary, but the large volumes make itlogistically challenging. Vehicles are also vulnerable to ash; it willclog lters and brake systems and abrade moving parts withinengines.

Finally, modern telecommunications networks appear to be rel-atively resilient to volcanic ash fall. Signal attenuation and interfer-ence during ash falls has not been reported in eruptions over thepast 20 years, with the exception of interference from ash plume-generated lightning. However, some telecommunications equip-ment is vulnerable to airborne ash, in particular HVAC systemswhich may become blocked from ash ingestion leading tooverheating.

9.2. Critical parameters for assessing ash impacts

Volcanic ash has a wide range of possible physical and chemicalcharacteristics, largely controlled by magma chemistry and erup-tion conditions. Climatic and environmental conditions will alsocontrol its dispersion and inuence its properties from site to site.This variability both between different eruptions and within thesame eruption makes it challenging to develop generic estimatesof ash impacts controlled by one parameter. Ash fall thicknesshas been the common parameter used for assessing the intensityof ash fall damage (e.g. Blong, 1984; Neild et al., 1998; etc.). Gen-erally this has been appropriate for relatively coarse level assess-ments of ash vulnerability. However, it tends to overlook otherash characteristics, which will inuence or even control the levelof damage incurred. However, this review, along with various otherrecent works (e.g. Johnston et al., 2000; Cronin et al., 2003;Witham et al., 2005; Stewart et al., 2006; Wilson et al., 2010a,b;Wardman et al., 2011), highlights that grain size, surface coatingcomposition, density and abrasiveness are also major controls onthe type and intensity of impact which can be expected followingash fall.

There has been signicant attention paid to the presence of athin surface coating on freshly-fallen volcanic ash, containing arange of readily-soluble salts as well as more slowly soluble com-ponents (Witham et al., 2005; Delmelle et al., 2007; Flaathen andGislason, 2007; Jones and Gislason, 2008). The composition of thissurface coating is important in determining the toxicological haz-ard posed by the ash (with uoride considered to be the primarytoxicological hazard) as well as the potential for contaminationof water supplies (Stewart et al., 2006, 2009a; Cronin et al.,

16 T.M. Wilson et al. / Physics and Chem2003). These readily-soluble salts are also thought to be importantin controlling both the electrical conductivity and the corrosive-ness of freshly-fallen ash although the relationships between these

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006properties and the surface coating composition are less well char-acterised than for contamination of water supplies.

We highlight ash grain size as a key impact parameter, but onewhich has arguably had less attention than ash thickness or surfacecoating composition. Fine-grained ash is generally dispersed far-ther from the erupting vent and thus can potentially affect moreinfrastructure components and systems. It is also more likely topenetrate equipment, adhere to equipment surfaces (includingdownwind and undersides of surfaces), carry a proportionallyhigher load of soluble salts due to its higher surface area, be moreeasily eroded and remobilised, and present a greater health hazard.

Other properties of ash that have also had less systematic atten-tion are abrasiveness, density and friability. The abrasive proper-ties of ash grains are a function of their hardness and shape. Ahigh degree of abrasiveness greatly increases the potential fordamage by both waterborne ash (turbines, sludge pump propel-lors) and airborne ash (air-cooled motors, cooling fans) and whenash is cleaned from surfaces such as airport runways and roofs.The density of individual particles inuences their behaviour, par-ticularly during cleanup operations, with denser particles beingmore difcult to move with a hose and more likely to form intrac-table deposits in underground drainage networks. However, denserparticles are less likely to be remobilised readily by wind. Bulkdensity of ash fall deposits (dry and wet) is also an important con-sideration in predicting ash loadings on buildings. Friability refersto the mechanical strength of ash grains; more friable particlesmay be compacted and ground up (e.g. by vehicles) and may affectthe re-use potential of the ash (e.g. as aggregate in concretemanufacture).

The remobilisation of volcanic ash can also lead to disruptionand damage to critical infrastructure. It is a well-acknowledgedhazard for transportation networks (Section 5). However, remobil-isation of thick ash deposits can occur over sustained periods at aregional scale, especially in dry, windy environments, which leadsto ongoing ash impacts on exposed critical infrastructure andwhich may be signicantly worse than the initial ash fall (Wilsonet al., 2010b). We highlight this as an important considerationfor future ash risk models, emergency planning and response.

These considerations strengthen the argument for ash hazardmodel outputs to include deposit thickness and grainsize in spatialand temporal contexts, and for damage curves (fragility functions)to capture other important characteristics of ash.

Finally, the condition of infrastructure prior to impact and thechanging demands following an eruption (direct or indirect) mayalso affect the potential for failure post-eruption.

9.3. Ash fall impact data collection

Ash fall impact data gathering can be standardized based on themethods used for this work, so that data can be collected collabo-ratively and reliably by institutes across the world, and covering allaspects of ash fall impacts from any one event. Reliability of data isessential and the methods used for data gathering should be stan-dardized to ensure high data quality. This will allow data sharing,collaborations and a repository of information for specic studies,without leaving blind spots in knowledge from any signicant ashfall event. Similarly protocols for laboratory testing of vulnerablecomponents should be developed. These measures will broadenthe knowledge on the consequences of volcanic ash falls, furtherour understanding of system vulnerability using eld and labora-tory methods, and allow a database to be built for use across areasof interest within ash impact studies. Such standardisation is beingaddressed by the Volcanic Ash Fall Impact Working Group of the

ry of the Earth xxx (2011) xxxxxxCities and Volcanoes Commission of the International Associationof Volcanology and Chemistry of the Earths Interior. Once vulner-ability is better understood, mitigation measures can be designed


mistrusing systems thinking tools and accounting for both direct andindirect ash fall impacts, to develop sustainable and complete solu-tions to increase system resilience.

9.4. Mitigation

Developing an understanding of the ways in which volcanic ashcan cause impacts on critical infrastructure may then enable man-agers to identify points of vulnerability within these systems,which may in turn suggest measures to reduce vulnerability toash fall. For example, in Quito, Ecuador, previous volcanic criseshave led to successful mitigation measures being adopted by watertreatment plant managers. Covers have been built over exposedplant such as clariers, treatment chemicals have been stockpiledand water supply lines have been re-routed to avoid known laharhazard zones (Leonard et al., 2005).

In a general sense, mitigation measures can include:

Covering exposed equipment (such as well-head pumps, stor-age tanks in water supply systems).

Monitoring key parameters (e.g. wear, contamination, distribu-tion, duration, thickness, ash characteristics).

Considering critical dependencies such as a continuous powersupply and making provision for backup generation

Maintaining equipment and plant in a good state of repair (forinstance, clean insulators are less at risk from ash-inducedashover).

Ensuring that supplies of essential equipment are well-stocked(e.g. spare lters, water supply treatment chemicals).

Ensuring that emergency plans for volcanic ash falls have beendeveloped and practiced in advance of a volcanic crisis.

Having a system in place (typically via volcanic monitoringagency) for rapid ash analysis of physical and chemical charac-teristics of ash, and distribution of ash in space and time.

9.5. Knowledge transfer

Our group has made it a priority to communicate the ndings ofour reconnaissance trips, supplemented by our laboratory-basedwork, to infrastructure managers, with the aim of reducing the vul-nerability of critical infrastructure to volcanic ash fall. In conjunc-tion with the Auckland Engineering Lifelines Group, we haveproduced a series of posters providing advice for infrastructuremanagers. The content of these posters has been reviewed foraccuracy and relevance by key staff from each infrastructure sec-tor. These posters are publicly available from the websitewww.aelg.org.nz, or from the authors of this paper.

A further web-based resource with useful information on volca-nic ash impacts on infrastructure is maintained by the US Geolog-ical Survey (http://volcanoes.usgs.gov/ash). This site also coversash impacts on human health, buildings and aviation. The UnitedKingdom-based website www.ivhhn.org has its main focus onhealth impacts of volcanic ash, but also includes useful resourcessuch as guidelines on preparedness for households, ash clean-upoperations, and ash sampling, collection and analysis guidelines.

9.6. Research gaps and future directions

In general, despite improved knowledge from reconnaissancetrip work, there is a lack of systematic and comprehensive docu-mentation of the behaviour of critical componentry and systems

T.M. Wilson et al. / Physics and Cheunder a wide range of volcanic ash conditions. This is being ad-dressed by the Volcanic Ash Fall Impacts Working Group men-tioned in Section 9.3. Following on from this, understanding the

Please cite this article in press as: Wilson, T.M., et al. Volcanic ash impacj.pce.2011.06.006interdependency and overall system functionality for modern soci-ety remains an important strategic goal.

Modern volcanic risk assessment and strong end-user informa-tion needs before, during and after an eruption crisis will continueto require the research community to provide robust estimates ofprobable impacts. Thus the ultimate goal of this research is to ableto provide accurate information for any type of volcanic ash andany impact intensity, ranging from minor nuisance to signicantdisruption or even total destruction. This presents a signicantchallenge given the wide range of physical and chemical proper-ties of volcanic ash (as discussed above), and the rapid growthand evolution of modern society. In particular, rapidly evolvingtechnology, increasingly interdependent systems and the low fre-quency of eruptions makes it difcult to determine whether exist-ing mitigation recommendations are relevant for modern or futureequipment.

Thin, distal ashfall is the volcanic hazard most likely to be expe-rienced by exposed critical infrastructure. However, previous stud-ies have often focused on very large eruptions and impactsassociated with ash falls >10 mm and do not report effects fromashfall

Johnston, D.M., 1997, Physical and Social Impacts of Past and Future VolcanicEruptions in New Zealand, Unpublished Ph.D. Thesis, University of Canterbury,

istChristchurch, 288 p.Johnston, D.M., Houghton, B.F., Neall, V.E., Ronan, K.R., Paton, D., 2000. Impacts of

the 1945 and 19951996 Ruapehu eruptions, New Zealand: an example ofincreasing societal vulnerability. Geologic

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