evolution and volcanic hazards of taapaca volcanic complex

7/27/2019 Evolution and Volcanic Hazards of Taapaca Volcanic Complex

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Journal of the Geological Society

doi: 10.1144/0016-764902-065

2004; v. 161; p. 603-618Journal of the Geological SocietyJ.E. Clavero, R.S.J. Sparks, M.S. Pringle, et al.of Northern ChileEvolution and volcanic hazards of Taapaca Volcanic Complex, Central Andes

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Journal of the Geological Society, London, Vol. 161, 2004, pp. 603618. Printed in Great Britain.

6 03

Evolution and volcanic hazards of Taapaca Volcanic Complex, Central Andes of

Northern Chile

J.E. CLAVERO 1,2, R .S. J. SPA R K S 2, M . S . P R I N G L E 3, E . P O L A N C O 1,4 & M . C . G A R D E W E G 1

1Servicio Nacional de Geologa y Minera, Av. Santa Mara, 0104-Santiago, Chile (e-mail: [email protected])2University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK

3Scottish Universities Reactor and Research Center (SURRC), East Kilbride G75 0QF, UK4Universidad Autonoma de Mexico (UNAM), Coyoacan 04510, Mexico D.F., Mexico

Abstract: Taapaca Volcanic Complex is a large dacitic volcano (35 km3) located in the western border of the

active zone of the Central Andes of Northern Chile. Apart from early poorly preserved silicic andesites,

Taapaca Volcanic Complex has generated remarkably similar porphyritic hornblendebiotite dacites with

distinctive sanidine megacrysts for at least 1.5 Ma. The main products of the volcano are dacite lavas and

domes with associated block-and-ash flow deposits. There have also been several sector collapses to generate

debris avalanches, which are closely associated with volcanic blasts and episodes of dome growth. Four stages

of evolution are recognized with volcanism occurring in short bursts between much longer periods of

dormancy. Volcanism has built a substantial stratovolcano and has migrated 4 5 km towards the SW with

time. Late Pleistocene to Holocene activity has involved at least three sector collapses of the hydrothermally

altered flanks and domes. Volcanic blasts, block-and-ash flows, debris avalanches and lahars have beendistributed down the southwestern flanks. These areas are the main populated part of the Chilean Altiplano

and the location of the main road between Bolivia and the Pacific Ocean coast. A future eruption will threaten

these areas and the regional economy.

Keywords: Central Andes, Holocene, debris avalanches, pyroclastics, volcanic risk.

Although Quaternary volcanism is widespread in the Altiplanoof Northern Chile (de Silva & Francis 1991), Holocene activityhas been little documented, with descriptions available from a

small number of volcanic centres: Guallatiri volcano (Gonzalez1995), Lascar volcano (Gardeweg et al. 1998) and Parinacotavolcano (Clavero et al. 2002). These volcanoes are mainly

located in desert areas and do not threaten populations. Taapaca(locally known as Nevados de Putre) had previously been consid-ered to be an extinct volcanic complex (Salas et al. 1966;

Gonzalez 1995). However, the first reconnaissance map of thevolcano was presented only recently by Kohlbach & Lohnert(1999). Geochronological and geochemical data for the volcaniccomplex demonstrating Late Pleistocene eruptive activity were

reported by Lohnert (1999) and Worner et al. (2000a).Taapaca Volcanic Complex is located in the Altiplano of

Northern Chile (Fig. 1) on the western border of the activevolcanic zone of the Central Andes (Fig. 1). Its highest summit

reaches 5850 m a.s.l. (above sea level) (188069S, 698309W), itsvolcanic products cover an area of more than 250 km 2 and themain edifice has an estimated minimum volume of 35 km3. This

paper describes the geological and geochemical evolution ofTaapaca Volcanic Complex, based on mapping carried out at1:25 000 scale (Clavero 2002). Mapping, accompanied by geo-

chronological (radiocarbon and 40Ar/39Ar), geochemical, physicalvolcanological and detailed stratigraphic studies document theevolution of Taapaca Volcanic Complex. Methods used for

mapping, and to obtain geochemical and geochronological data(including discussion on sample results), have been presented indetail by Clavero (2002).

The new observations of Taapaca Volcanic Complex have

implications for several general volcanological problems. Volca-nic activity here has been persistent during the last 1.5 Ma and

its eruptive history suggests that Taapaca Volcanic Complex isnot extinct. Injections of new batches of mafic magma have beenimportant for triggering dacitic eruptions. The activity of Taapa-

ca Volcanic Complex is mainly characterized by debris ava-lanches and dome growth with associated block-and-ash flowsand highly destructive volcanic blasts. Putre, the main village in

the Chilean Altiplano, is built on top of these pyroclasticdeposits, some younger than 8 ka bp. Moreover, the volcano isclose to the main highway between Bolivia and the Pacific coast

(Fig. 2). Taapaca Volcanic Complex has had a previouslyunknown history of violent volcanic eruptions during the LatePleistocene to Holocene and is not an extinct volcano. Futureactivity at Taapaca Volcanic Complex therefore represents a

threat to the most populated area of the Altiplano of NorthernChile and to economic activities in the region.

Analytical techniques

Geochronology

Radiocarbon. Samples of peat, palaeosoil, organic-rich fallout ash layersand carbonized wood contained in pyroclastic flow deposits were taken inthe field, avoiding contamination with young carbon, and packed in

aluminium foil packets. Conventional analyses were carried out atIsotrace Radiocarbon Laboratory (University of Toronto) and AMS

analyses were performed at Rafter Laboratories (New Zealand).

Sample ages are quoted as uncalibrated conventional radiocarbon dates

in years before present (bp), using the Libby 14C mean life of 8033 a.

The errors represent the 68.3% confidence limit.

40Ar/39Ar. Samples were selected following the petrographic criteria of

Maniken & Dalrymple (1972), mainly choosing holocrystalline (as much

as possible) unaltered rocks.


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Fig. 1. Location and regional geological map of the study area, within Northern Chile.

Fig. 2. Satellite TM Landsat image (bands

7,4,1) of Taapaca Volcanic Complex area,

showing its major geological features and

the location of Putre, the main village of

the Chilean Altiplano. Snow and ice in blue

and vegetation in green. The deep Lluta

Valley can be seen to the left. The white

dashed lines mark the international Chile

Bolivia road (to the east) and the road to

Visviri and Peru (to the north).

J. E. CLAVERO ET AL .604


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Groundmass separates consisted of 100250 mg of the 250500 mm

sieve fraction. All distinct phenocrysts phases were eliminated by

handpicking to better than 99% purity. Biotite separates of 125250 mmsieve fraction were prepared by magnetic and heavy liquid separation.

Feldspar (including sanidine and plagioclase) separates were handpicked

from a 62125 mm sieve fraction crushed from megacrysts. Mineral andgroundmass separates were loaded in 99.99% copper foil packets.

Neutron flux standards were loaded in aluminium foil packets, and loaded

in 6 mm (internal diameter) quartz vials at intervals between 20 and

30 mm, intercalated with the samples. The monitor mineral used was the

27.92 Ma USGS (US Geological Survey) sanidine 85G003 from theTaylor Creek rhyolite (Dalrymple & Duffield 1988). The quartz vials

were irradiated at 1 MW for 30 min in the Cd-shielded CLICIT facility at

the Oregon State University Triga reactor.After 26 months the samples were analysed at SURRC (Scottish

Universities Research and Reactor Centre). Incremental step-heating

experiments comprising 1018 steps were carried out either in a double

vacuum resistance furnace, attached to a small volume gas clean-upsystem with SAES ZrAl C50 getters at 400 8C and a zeolite finger, or

with a CO2 laser beam. Temperatures reported for incremental steps are

as calibrated by optical pyrometry in the case of furnace experiments.

After 15 min heating and 1015 min further clean-up with an additionalZrAl C50 getter at room temperature, isotopic analysis of the purified

gas was carried out on an ultrasensitive rare-gas mass spectrometer (Mass

Analyser Products 215), with a modified Nier source and variable slit.On the basis of previous work (Wijbrans et al. 1995), the reactor

corrections for interfering neutron-induced reactions of 40K and 40Caare as follows: [40Ar=39Ar]K 0:00086; [

36Ar=37Ar]Ca 0:000264;[39Ar=37Ar]Ca 0:000673. The decay constants of Steiger & Jager(1977) were used in age calculations. J values were determined from the

mean of 10 laser fusion analyses from each monitor packet. Comparison

of the J curve with individual monitor estimates suggests that a

conservative error in J for samples is 0.3 0.5%.Samples ages were calculated from both plateau and isochron analyses.

Plateau ages were calculated as weighted means, where each age is

weighted by the inverse of its variance (Taylor 1982), and involve a

single variable mean square weighted deviation (MSWD) calculation to

test for excess scatter. Isochron ages were calculated using the cubicleast-squares regression with correlated errors (York 1969). All errors are

reported as one standard deviation of the analytical precision, and allsignificant tests were carried out at the 95% confidence level.

Geochemistry

Thirty-eight samples were selected in the field to be representative of all

four evolutionary stages of Taapaca Volcanic Complex. Unaltered rockswere taken, avoiding slightly to strongly hydrothermally altered rocks.

Samples of 0.51 kg were taken from those rocks that were slightly

porphyritic (mainly Stage I), and samples of 2 3 kg were taken from

those with sanidine megacrysts to avoid the lack of sample homogeneitycaused by the presence of large phenocrysts.

Major and trace element chemical analyses were carried out at the

Chilean Geological Survey laboratories (SernageominChile). Sampleswere crushed to less than 200 sieve size and then analysed by atomic

absorption spectrometry (AAS) for major oxides, and by inductively

coupled plasma-atomic emission spectrometry (ICP-AES) for trace

elements. Errors in the methods used by Sernageomin geochemical

laboratory are usually less than 0.5% for major oxides and less than 3%for trace element. These results are permanently calibrated with interna-

tional standards.

Geology

Basement

Taapaca Volcanic Complex is on the western edge of an uplifted

high plateau developed between two mountain ranges, theWestern and Eastern cordilleras, both of which have been builtsince the Late Oligocene (Garca 2001; Garca et al. 2004). The

Western Cordillera is formed by rocks ranging in age fromPrecambrian to Miocene (Pacci et al. 1980; Worner et al. 2000b;Garca 2001; Fig. 1), uplifted on a west-vergent thrust systemmainly during the Miocene (Munoz & Sepulveda 1992; Munoz

& Charrier 1996; Garca et al. 1999; Garca 2001). TaapacaVolcanic Complex started its eruptive activity c. 1.5 Ma ago ontop of this uplifted cordillera, about 20 km to the west of themain Quaternary volcanic chain (Fig. 1). To the west and south

(Figs 1 and 3), the basement of the volcanic complex is formed

by a strongly deformed Upper Oligocene Lower Miocene volca-niclastic sequence known as the Lupica Formation (Montecinos1963; Pacci et al. 1980; Garca 2001). The Lupica Formation ishere largely made of rhyolitic ignimbrites, andesite lavas andepiclastic rocks. These units have been strongly folded and thrust

during the Miocene (Garca et al. 1999; Munoz & Sepulveda1992; Munoz & Charrier 1996). To the east and south (Figs 2and 3) Taapaca Volcanic Complex was built on top of mainlyandesitic volcanic and volcaniclastic sequences of Mid- to Late

Miocene to Pliocene age (Garca 2001; Garca et al. 2004). Tothe north (Figs 2 and3), the basement is formed by Mio-Pliocenelacustrine sedimentary sequences of the Huaylas Formation(Salas et al. 1966; Garca et al. 2004), and the Pliocene rhyolitic

Lauca Ignimbrite (Worner et al. 2000a; Garca 2001).

Taapaca Volcanic Complex

Having long been considered an extinct volcano, TaapacaVolcanic Complex has been the focus of only a few geologicalstudies. Kohlbach & Lohnert (1999) produced a reconnaissancegeological map of Taapaca Volcanic Complex, dividing its

history into three stages, based mainly on mapping (1:25 000)and geochemical data. Lohnert (1999) studied the chemistry of a

sanidine megacryst and reported the first Late Pleistocene 40Ar/39Ar age date for Taapaca Volcanic Complex. Worner et al.(2000a) followed the three evolutionary stages proposed by

Kohlbach & Lohnert (1999) and published a few more 40Ar/39Ardates.

Figure 3 is a reduction of the new 1:40 000 scale geologicalmap of Taapaca Volcanic Complex and surrounding areas

(Clavero 2002). On the basis of this mapping, as well asgeochronological, geochemical and stratigraphic criteria, theeruptive history of Taapaca Volcanic Complex has now beendivided into four stages, adding a previously unrecorded stage to

the scheme of Kohlbach & Lohnert (1999). These stages show anevolution from a volcano composed of andesite lavas (Stage I),to a steep-sided lava-dome complex (Stage II), to a dome

complex and associated debris and pyroclastic deposits in its twoyoungest stages. This evolution has been accompanied bymoderate compositional changes. A migration of the main focus

of eruptive activity also occurred towards the SSW by 45 km.

Stage I (Pliocene Early Pleistocene?). The only outcrops arelocated in the basal part of the northern flank of TaapacaVolcanic Complex (Figs 2 and 3). They consist of two silicicandesite lava flows (6061% SiO2, Table 1, Fig. 4), with asmoothed eroded morphology, and no preservation of primarystructures, such as flow ridges or levees. The flows (,60 m

thick), partially covered by younger Stage II pyroclastic deposits,extend at least 6 km in a northsouth direction (Fig. 3). They aremoderately porphyritic (up to 15 vol.% phenocrysts) with plagio-clase, clinopyroxene and orthopyroxene, and occasional amphi-

bole and sanidine. No radiometric dates have been obtained sofar from these flows, and so it is only possible to say that theyare older than 1.5 Ma.

E VO LU T IO N OF TA A PAC A VO L C A N IC C O M P L EX 605


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Fig. 3. Taapaca Volcanic Complex geological map (reduction from 1:40 000 scale map ofClavero 2002).



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Stage II (Early Late Pleistocene, 1.5 0.5 Ma). The rocks anddeposits of this stage form the main part of the northern andeastern flanks of the volcanic complex, and a small part of the

southwestern flank, covering a total area of more than 150 km 2

(Fig. 3). They consist mainly of lavas, domes, block-and-ash flowand lahar deposits. Stage II products are porphyritic (up to 18

20 vol.% phenocrysts) and are mainly dacites (6268% SiO2,Table 1, Fig. 4), containing sanidine megacrysts (up to 23 cm),

plagioclase, biotite, quartz and amphibole phenocrysts, withminor proportions of clinopyroxene and titanite. Mafic inclusions

(,1 vol.%) are found in most products. They have smoothcircular to oval shapes (,15 cm in diameter), chilled margins,

skeletal textures (dyxitaxitic texture) and are composed mainlyof a microcrystalline aggregate of plagioclase, hornblende andmagnetite. Occasionally the inclusions also contain quartz,

biotite and/or sanidine crystals commonly showing reaction rims,which are thought to be xenocrysts incorporated from the hostdacite.

Lavas form the main part of the northern and eastern flanksand a small part of the southwestern flank (Figs 3 and 5ad).They are usually thick (60150 m) with a maximum length of3 km (Fig. 5b and c). Primary morphologies, such as flow ridges,

are preserved especially on the eastern flank. On the northernand eastern flanks the lavas have been more strongly affected by

Table 1. Major elements geochemical data from Taapaca Volcanic Complex products

Sample UTM coordinates Stage/Unit SiO2 Al2O3 TiO2 Fe2 O3 FeO CaO MgO MnO Na2 O K2O P2 O5 H2O C S Total

N E

CAL-13 7988952 4 42817 IV/Socapave 65.20 15.95 0.71 2.07 1.40 3.75 1.50 0.05 4.54 3.41 0.28 0.81 0.04 0.01 99.72CAL-16 7990395 446055 IV/Putre 64.33 15.79 0.81 2.28 1.81 4.29 1.90 0.06 4.32 3.10 0.32 0.94 0.02 0.01 99.99CAL-32 8000822 445413 II 63.34 16.04 0.86 2.81 1.42 4.06 1.87 0.06 4.20 2.99 0.31 1.60 0.02 0.01 99.59CAL-34 8000822 445413 II 65.40 15.79 0.59 2.92 0.48 3.51 1.41 0.06 4.15 3.25 0.31 1.76 0.03 0.02 99.68CAL-36 8004209 448135 II 61.55 16.96 1.01 4.08 1.13 4.53 2.11 0.08 4.36 2.87 0.41 0.68 0.01 99.77CAL-38 7993502 443367 IV/Putre 63.32 1 5.98 0.93 2.78 1.89 4.63 2.12 0.06 4.35 2.86 0.34 0.26 0.01 99.53CAL-116A 7999476 442445 IV/Tajane 63.22 16.39 0.95 3.02 1.58 4.35 2.01 0.06 4.46 3.18 0.31 0.25 0.01 99.79CAL-116B 7999476 442445 Mafic inclusion 54.59 16.62 1.63 5.72 2.18 6.86 4.29 0.09 3.91 2.73 0.51 0.75 0.03 99.92CAL-117 8000090 443433 IV/Putre 65.50 16.43 0.55 1.95 1.31 3.27 1.32 0.05 4.29 3.26 0.13 1.78 99.85CAL-120 8007014 443147 II 63.24 16.20 0.85 2.52 1.65 4.10 1.91 0.06 4.15 3.71 0.28 1.02 0.01 99.70CAL-121 8006298 442887 I 60.37 16.60 0.98 4.11 1.48 4.72 2.30 0.09 4.17 3.44 0.28 1.11 0.01 99.65CAL-123 8004600 442640 I 59.45 17.46 1.07 3.19 2.51 5.04 2.39 0.08 4.11 3.43 0.36 0.80 0.05 99.93CAL-124A 7987788 440673 IV/Tajane 65.82 1 5.96 0.75 2.35 1.41 3.74 1.70 0.05 4.44 3.46 0.22 0.04 99.95CAL-124C 7987788 440673 IV/Tajane 64.30 15.95 0.90 2.47 1.85 3.95 1.97 0.06 4.41 3.31 0.22 0.21 0.01 99.62CAL-124E 7987554 440512 IV/Churilinco 65.49 16.20 0.72 3.98 0.09 3.84 1.92 0.06 3.66 3.39 0.18 0.32 0.01 99.87CAL-128C 7 990348 4 41936 IV/Socapave 65.63 15.66 0.70 2.72 1.03 3.43 1.47 0.05 4.32 3.46 0.17 1.09 0.05 0.03 99.81CAL-131 7989956 444332 IV/Socapave 62.89 16.18 0.92 3.02 1.74 4.39 2.09 0.06 4.35 3.07 0.25 0.69 0.03 99.68CAL-136 7990536 436398 IV/Tajane 64.46 16.01 0.63 2.51 1.24 4.10 1.76 0.06 4.29 3.23 0.14 1.31 99.74CAL-138A 7999348 445557 IV/Tajane 63.99 15.74 0.90 3.00 1.61 4.34 2.38 0.06 4.31 3.12 0.23 0.06 0.01 99.76CAL-138B 7999348 445557 Mafic inclusion 52.18 16.27 1.77 5.75 3.54 7.28 6.41 0.10 3.86 2.00 0.46 0.12 0.01 99.75CAL-139 8003022 448553 II 63.66 16.03 0.95 2.45 1.95 3.82 1.77 0.05 4.15 3.43 0.24 1.08 0.01 99.59CAL-140 8007216 451755 II 63.95 16.02 0.88 2.50 1.80 3.93 1.80 0.06 4.31 3.43 0.24 0.95 99.88CAL-141 7994367 442667 II 62.73 16.54 0.72 3.18 1.77 4.76 2.35 0.06 3.80 3.19 0.17 0.58 0.01 99.87CAL-142 7999650 447450 II 63.25 15.83 0.78 3.62 0.32 2.33 0.80 0.04 3.78 3.37 0.19 3.30 2.09 99.71CAL-143 7999450 447280 III 65.74 1 5.50 0.78 2.59 1.37 3.79 1.72 0.05 4.41 3.31 0.21 0.43 0.04 99.96CAL-147 7998619 4 45277 Mafic inclusion 53.70 17.64 1.18 6.31 2.35 7.64 4.56 0.13 3.38 1.80 0.28 0.86 0.01 99.85CAL-147A 7998619 445277 IV/Tajane 62.14 15.85 0.83 3.46 2.04 4.94 2.77 0.09 3.88 2.79 0.18 0.95 0.01 99.92CAL-148 7998511 445378 IV/Socapave 65.68 15.40 0.80 2.90 1.10 3.71 1.72 0.05 4.39 3.39 0.20 0.41 0.01 99.75

CAL-148A 7998511 445378 Mafic inclusion 58.92 16.30 1.30 4.79 1.74 5.34 3.02 0.08 4.29 2.83 0.37 0.48 0.05 0.01 99.52CAL-149 7998390 445003 III 66.22 15.52 0.70 2.99 0.76 3.27 1.53 0.05 4.31 3.60 0.17 0.66 99.78CAL-150 7998154 444562 IV/Socapave 66.85 15.45 0.73 3.45 0.26 3.29 1.51 0.05 4.41 3.63 0.17 0.03 0.05 99.89CAL-152 7991595 448127 IV/Putre 65.91 15.34 0.82 2.34 1.63 3.69 1.78 0.05 4.34 3.46 0.20 0.30 0.02 99.89CAL-153 7994246 445684 IV/Churilinco 61.08 16.01 1.01 3.17 1.73 4.64 2.25 0.08 4.25 3.56 0.32 1.56 0.01 99.68CAL-157 7996142 442723 III 62.63 16.60 0.96 3.38 1.12 4.29 1.77 0.06 4.50 3.22 0.26 0.84 99.64

CAL-167 7996840 448687 IV/Churilinco 60.31 15.78 1.15 3.32 2.13 5.02 2.41 0.08 4.44 2.93 0.31 1.94 0.01 99.83CAL-168 7996576 448820 III 63.38 15.96 0.89 3.26 1.24 4.34 2.01 0.08 4.58 3.64 0.26 0.25 99.88CAL-169 7995172 448211 II 62.03 16.05 1.07 2.79 2.29 4.64 2.38 0.08 4.21 3.26 0.24 0.65 0.02 99.72CAL-170 7993955 447458 II 66.68 15.55 0.58 1.87 0.97 3.20 1.17 0.05 4.37 3.94 0.19 1.28 99.86

Fig. 4. Whole-rock geochemistry of selected Taapaca Volcanic Complex products.



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glacial erosion, and also locally affected by silicic and clay-rich

hydrothermal alteration. Two domes of different shape and sizehave also been recognized (Fig. 3).

Block-and-ash flow deposits are located mainly on the north-ern and northwestern flanks, covering an area of more than

110 km2 (Figs 3 and 5a). Despite their smoothly eroded surfaces,at least 16 flow units have been recognized. Individual depositthicknesses vary from 20 m in proximal facies, to less than 2 min distal facies. Their run-outs range from c. 6 km to over 13 km,

with some reaching the Lluta valley (Figs 2 and 3). The depositsconsist mainly of a monomict dacitic breccia, with rounded tosubrounded blocks up to 4 m in diameter, many of them showing

prismatically jointed block structures (Cas & Wright 1987),within a mainly monomict matrix of fine to medium ash size.They show poorly defined subhorizontal bedding, and individual

flow units have a tendency to show reverse grading.Lahar deposits (up to 5 m thick) crop out in the distal areas in

gradual transition from Stage II block-and-ash flow deposits (Fig.

3). They consist mainly of similar material to the block-and-ashflow deposits, but contain many accidental lithic fragments (upto 50 vol.%) within a sandy matrix. The largest fragments areless than 80 cm in diameter and are usually located at the bottom

or middle of individual flow unit deposits, which are less than2 m thick.

Four 40Ar/39Ar dates were obtained from lavas and domes of

this unit (Table 2). One of them gave an anomalous result(8565.1 66.9 ka), probably owing to xenocrystic feldspar con-tamination, as has been documented to occur in other domecomplexes (Harford 2001; Harford et al. 2002). The other three

dates, and one consistent published age of c. 1.2 Ma (Worner etal. 2000a), indicate that the Stage II edifice was formed between1.5 and 0.5 Ma.

Taking into account the spatial distribution of the units,

primary dips and location of the hydrothermal alteration zones(Figs 3 and 5b), it is proposed that the original edifice, builtduring Taapaca Stage II, was a voluminous stratovolcano (Fig.

5b). However, it is only the northern flank of this ancestraledifice that remains (Fig. 5b). The missing part of the southernflank was probably eroded by glaciers and affected by a huge

sector collapse, which generated the Churilinco debris avalanchedeposit (discussed below).

Stage III (Late Pleistocene, 0.50.47 Ma). Stage III consists ofdacite lavas, domes and associated block-and-ash flow deposits(6367% SiO2, Table 1, Fig. 4), mainly located in the central

part of the volcanic complex and on the southwestern and easternflanks, covering an area of over 18 km2 (Fig. 3). The dacites aresimilar to those of Stage II, with a slightly higher proportion of

Fig. 5. (a) Taapaca Volcanic Complex viewed from the north, showing the remnant of Stage II edifice and its northern pyroclastic fan in the foreground.

To the east, a Stage III torta-type dome can be observed. (b) Taapaca Volcanic Complex viewed from the north (closer than ( a)), showing the

hydrothermally altered core and the possible shape of the ancestral edifice, based on the morphologies of the remnant flanks. ( c) Northwestern flank of

Taapaca Volcanic Complex, showing Stage II and III lavas partially covered by a Tajane Unit dome. ( d) Taapaca Volcanic Complex viewed from the east,

showing its southeastern flank formed by Stage II lavas covered by a series of Stage III domes. The highest peak of Stage IV domes can be seen in the

background.



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both sanidine megacrysts (up to 3 4 vol.%), which are up to 45 cm long, and mafic inclusions (up to 23 vol.%).

Lavas are mainly located on the western flanks (Figs 3 and5c). They are typically thick (60120 m) and their maximum

length is 2 km. Primary structures include flow ridges smoothedby erosion (both glacial and alluvial), and some of them preserveblocky surfaces.

Domes are mainly located on the eastern flank, and show anorthsouth alignment. A flat torta-type dome occurs in the

north (Fig. 5a). Such flat morphologies are common in theCentral Andes (de Silva et al. 1996; Watts et al. 1999). There areseveral shear zones between different dome lobes, similar tothose recently described from the Soufriere Hills dome, Mon-tserrat (Watts et al. 2002). The southern ones crop out 1 km to

the south of the torta-type, and are aligned in a northsouthtrend 4.5 km long (Figs 3 and 5d).

Block-and-ash flow deposits are mainly located on the north-western flank of Taapaca Volcanic Complex (Fig. 3). Their

individual thickness varies from 1520 m near the source to lessthan 3 m in distal areas. Their petrographic and internal structur-al features are similar to Stage II block-and-ash flow deposits.

No radiometric data have been obtained from Stage III rocks.

However, dates from the youngest Stage II lava and the oldest

Tajane Unit (Stage IV) flow (Table 2) constrain Stage II activityto a short period between 0.5 and 0.47 Ma.

Stage IV (Late PleistoceneHolocene, 0.45 Marecent). Thisstage consists of a series of dacite (6268% SiO2, Table 1, Fig.4) domes and associated deposits from block-and-ash flows,debris avalanches, blasts, tephra fallout, rock falls, pyroclastic

flows and lahars, which cover an area of more than 80 km 2. Thedomes and their deposits form the main edifice and pyroclastic

fans in the southern and southwestern part of the complex (Figs3 and 6a, b). Most of the pyroclastic deposits are cut by deepgullies, which have developed in the last 40 ka. The town of

Putre is built on top of one of these major pyroclastic fans.Three distinct Stage IV terraces, cut into the pyroclastic fans,

can be identified in the area of Putre (Fig. 3). Each terracerepresents a fan of younger pyroclastic deposits infilling valleys

cut in older fans. The porphyritic dacite (up to 40 vol.%phenocrysts) is characterized by sanidine megacrysts (up to12 cm long, some of them having euhedral shapes), plagioclase,

biotite, amphibole and quartz phenocrysts, and occasional clin-

opyroxene, within a fresh glassy to trachytic groundmass withplagioclase and sometimes hornblende microlites, as well as tinyFeTi oxide crystals. Mafic inclusions are ubiquitous and formup to 56 vol.% of the juvenile material. A series of stratigraphic

columns were constructed, four of which are summarized inFigure 7, corresponding to the most representative sections

located in the surroundings of the village of Putre. From thesestratigraphic columns, four subunits have been recognized.

Churilinco Unit (Late Pleistocene, 430 450 ka). The oldest unit,consisting of a debris avalanche deposit and a thick lava flow,has been recognized only on the southern flank (Fig. 3). The

outcrops cover an area of only c. 1 km2, as the unit has beeneroded by younger debris avalanches or buried by pyroclastic

deposits (Fig. 7).The Churilinco debris avalanche deposit crops out at the

bottom of Quebrada Socapave. It consists of a monomict daciticbreccia (65% SiO2, Table 1, Fig. 4), semi- to strongly consoli-

dated, with mainly angular fragments up to 2.5 m in diameter,within a medium-grained reddish matrix of the same composi-tion. It shows a hummocky upper surface and contains manyT

able2.

40Ar/39Argeochronologydata

ofTaapacaVolcanicComplex

Sample

UTMcoordinates

Stage/Unit

Material

Whole-rock

K2O(wt%)

TotalK/Ca

TotalAra

m

ol/g

Totalfusion

age(ka)

1

N

Increments

used(8C)

39Ar(%)

Agespectrumanalysis

Inverseisochronamalysis

N

E

Age

1(ka)

MSWD

SUMS

40Ar/36Ar

1

intercept

Age

1(ka)

Furnace

CAL-38

7993502

443367

IV/Tajane

Groundmass

2.88

1.911983

3.20E

14

5.2

8.6

6of14

693986

60

19.56

4.0

1.78

2.41

297.6

2.4

11.3

9.4

CAL-105

7995500

445100

IV/Tajane

Biotite

n.a.

119.9473

6.55E

14

156.7

7.9

7of17

8631101

67.4

114.66

5.3

2.70

3.18

296.7

1.6

104.6

13.2

CAL-13

7988952

442817

IV/Socapav

e

Groundmass

3.41

3.891494

3.82E

14

44.1

2.9

5of13

493749

71.5

24.96

6.6

10.60

2.65

310.3

3.2

19.3

10.2

CAL-13

7988952

442817

IV/Socapav

e

Biotite

3.41

41.56245

5.24E

14

149.4

8.3

6of21

911986

59.3

102.0

6.7*

4.27

0.49

302.3

1.8

40.8

16.5*

CAL-108

7996600

444900

IV/Tajane

Biotite

n.a.

41.35194

5.57E

14

66.0

3.9

12of36

860981

73.6

41.86

3.4

2.46

4.32

294.4

0.8

53.5

7.2

CAL-98

800000

450700

II

Biotite

n.a.

96.54967

6.04E

14

2200.9

8.8

6of20

9861142

66.2

2163.36

10.1

1.71

0.65

300.3

2.1

2113.3

24.2

Laser

CAL-166

7994050

447150

IV/Socapav

e

Feldspar

n.a.

1.882645

1.50E

15

35.9

1.7

5of11

n.a.

56.7

14.96

1.3

0.59

0.71

289.7

17.3

16.7

6.1

CAL-124E

7987554

440512

IV/Churilinco

Feldspar

3.39

0.1816166

1.51E

15

587.4

9.8

7of11

n.a.

90.3

595.06

7.9

1.26

2.46

298.3

5.5

622.3

31.2

CAL-138A

7999348

445557

IV/Tajane

Feldspar

3.12

0.429699

2.91E

15

240.9

13.1

7of11

n.a.

81.2

262.26

8.2

2.77

4.57

296.4

3.2

281.2

15.6

CAL-170

7993955

447458

II

Feldspar

3.94

0.1774603

1.31E

15

687.7

18.0

4of10

n.a.

52.8

495.66

20.0

3.60

5.03

338.3

77.9

382.4

200.1

CAL-116A

7999476

442445

IV/Tajane

Feldspar

3.18

0.8192181

5.09E

15

426.8

6.3

5of10

n.a.

75.1

427.76

3.5

2.21

2.67

305.6

14.2

418.3

13.0

CAL-140

8007216

451755

II

Feldspar

3.43

0.1822443

1.48E

15

1606.1

504.6

6of11

n.a.

61.1

1464.16

69.1

1.42

6.2

292.3

2.9

1804.9

299.2

CAL-141

7994367

442667

II

Feldspar

3.19

0.09150907

1.04E

15

8465.5

33.8

9of12

n.a.

79.7

8565.1

66.9*

8.58*

10.31

305

22

8760

135

n.a.,notavailable.

N,numberofheatinginc

rementsusedinregression.Valueinboldisthepreferredageforeachsample.

*Notreliableage(seetextfordiscussion).



9/17

blocks with jigsaw fractures. However, there is no evidence forhot emplacement. The morphology, composition and distributionof the Churilinco debris avalanche deposit indicate an origin by

partial sector collapse of the ancestral Stage II and III edifices.

A block within the avalanche deposit was dated at595.0 7.9 ka (40Ar/39Ar in feldspar, Table 2). This date isinterpreted to represent the eruption age of a Stage II lavainvolved in the collapse and therefore gives only a maximum age

for the deposit. The age of the Churilinco Unit is alsoconstrained by the oldest date available from the overlyingTajane Unit, which is c. 430 ka, and by the youngest date from aStage II flow, which is c. 500 ka (Table 2). However, all Stage III

products were also erupted in that period, which means that it islikely that the Churilinco Unit was formed slightly before theTajane Unit in the period 430450 ka.

Tajane Unit (Late Pleistocene, 43025 ka). This unit covers an

area of more than 30 km2 on the southern and southwesternflanks (Fig. 3). It consists of a series of dacite lavas, domes, adebris avalanche deposit, and a sequence of pyroclastic depositsthat includes block-and-ash flow, blast, tephra fallout, ash-cloud

surge and lahar deposits (Fig. 7). The lava flows, with well-preserved flow ridges and blocky surfaces, consist of thick aa toblocky lavas (up to 80 100 m thick) up to 3 km long (Fig. 3).

Two domes occur on the western flanks, overlying Stage IIIlavas (Figs 5c and 6b), the southern one being cut by SocapaveUnit domes. They are emplaced on very steep slopes and showwell-preserved lobes, blocky surfaces and parallel to folded flow-

banding.The Tajane debris avalanche deposit crops out on the southern

flank (Fig. 3). It consists of an unconsolidated to semiconsoli-dated breccia, which has a hummocky surface gently smoothed

by erosion, and partially infilled by younger pyroclastic deposits.It contains mainly monomict dacitic angular fragments up to

2.5 m in diameter, some of which have prismatically jointedblock structures, suggesting hot emplacement. The matrix ispoorly sorted and consists of almost the same material, which isof medium to fine lapilli size.

Pyroclastic deposits are distributed in two major fans on thesouthern and southwestern flanks, covering an area of more than25 km2 (Fig. 3). The maximum thickness of the pyroclastic

sequence is 80 m. It mainly consists of block-and-ash flowdeposits, which are similar in petrography and structures to StageII and III block-and-ash flow deposits. Gas segregation pipes areusually found in the upper part of individual flows, and are

commonly cut by overlying ash-cloud surge deposits. Their run-outs range from a few kilometres to 13 km from the source area.Thin (,20 cm thick), fine-grained ash-cloud surge deposits withwell-developed cross-lamination and dune structures are com-

monly found on top of block-and-ash flow deposits, but lackcontinuity. Some blast and lahar deposits have also beenrecognized within the sequence (Clavero 2002).

Four 40Ar/39Ar and one radiocarbon dates have been obtained

from lavas and deposits of this unit (Tables 2 and 3). The oldestdate (c. 430 ka, Table 2) was obtained from a block-and-ash flowdeposit, and the youngest one (c. 25 ka, Table 3) was obtained

from the upper part of the pyroclastic sequence, which forms theterrace on which the village of Putre is built.

Socapave Unit (Late PleistoceneEarly Holocene, 259 ka).

This unit covers an area over 25 km2 on the western and southernflanks. It consists of a series of lava domes, a debris avalanche

deposit and a sequence of pyroclastic deposits that includesblock-and-ash flow, rock-fall, blast, tephra fallout and secondarypyroclastic flows (Fig. 7).

The Socapave domes are located on the western border of thevolcanic complex (Figs 3 and 6a). They have blocky surfacesand very irregular shapes as they have been affected by erosionand a sector collapse, which generated the Socapave debris

avalanche (Fig. 3).The Socapave debris avalanche deposit (Fig. 6a) covers an

area of over 20 km2, and reaches a distance of more than 10 km

(Fig. 3). It has a well-defined hummocky surface (Fig. 8a), withhummocks up to 35 m high, in places smoothed by erosion and

by the infilling of younger pyroclastic deposits (Figs 8b and 9a).

The deposit consists mainly of a monomict dacitic breccia,formed by angular fragments up to 10 m in diameter, many with

prismatically jointed block structures. The matrix is mainlycomposed of the same material fragmented to a medium to

coarse ash size (Fig. 8a). Gas segregation pipes structures, whichare not usual in debris avalanche deposits, are common at the topof the deposit, suggesting a hot emplacement related to juvenile

Fig. 6. (a) Taapaca Volcanic Complex viewed from the SW, showing the major features of the southwestern flanks: Socapave and Putre domes, the

Socapave debris avalanche deposit, and Putre Unit pyroclastic deposits around the Putre village area. (b) Taapaca Volcanic Complex viewed from the

west, showing, from left to right, the western flank of the ancestral Taapaca II edifice, Stage III domes and Stage IV domes, which show the southern

migration of the focus of eruptive activity through time.



10/17

Fig.

7.StageIVpyroclasticstratigraphyaroundthePutrevillagearea,showingthemainpyroclasticdepositsofTaapacaVolcanic

ComplexLatePleistocenetoHoloceneeruptiveactivity.PJB,prismatically

jointedblock.



11/17

material. A blast deposit infills fractures developed in theavalanche deposit, showing that the sector collapse was immedi-ately followed by an explosion (Fig. 8b). Blast fragments appear

incorporated downstream within the debris avalanche deposit.The distal parts of the avalanche deposit are located at theeastern outskirts of the village of Putre (Fig. 6a).

The pyroclastic deposits mainly consist of block-and-ash,blast, tephra fallout and secondary pyroclastic flow deposits (Fig.7). This sequence is generally less than 50 m thick withindividual flow unit thickness ranging from few centimetres to

20 m. These deposits form part of the southern fan, overlyingTajane Unit deposits, and are overlain by younger Putre Unit

deposits (Fig. 10a). Block-and-ash flow deposits vary from 10 mto less than 1 m thick, with run-outs of over 8 km. They aremainly composed of rounded to subrounded dacitic fragments

(up to 1 m in diameter), many of them showing prismaticallyjointed block structures (Fig. 10b). Gas segregation pipe struc-tures are common, especially in the upper parts of the deposits.

Several block-and-ash flow units are overlain by thin (less than20 cm thick), fine-grained, ash-cloud surge deposits. Sometimesthin layers (less than 2 cm thick) of fine-grained co-pyroclasticflow ash fallout (Bonadonna et al. 2002) are preserved on top of

the surges. Blast deposits are usually less than 2 m thick, andshow two distinctive layers, the lower one being coarser-grained

Table 3. Uncalibrated radiocarbon dates of peat, paleosoil horizons and carbonized wood from Taapaca Volcanic Complex area

S tr at ig rap hi c un it UT M coo rd ina te s Mat er ial D at e ( yea rs b p) * Met ho d S tr at igr aph ic si gn ifi can ceand sample

number N E

Putre Unit

CAL-24 7987470 441675 Carbonized wood 8970 100 AMS Carbonized wood on palaeo-soil horizon developed on top of Socapave deposits. Age ofthe base of Putre Unit

CAL-23D 7992546 444925 Peat 7440 60 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

CAL-23F 7992546 444925 Peat 6570 70 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

CAL-23I 7992546 444925 Peat 4900 70 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

CAL-23K 7992546 444925 Ash layer withorganic material

4350 70 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

CAL-23J 7992546 444925 Peat 3530 70 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

CAL-23L 7992546 444925 Peat 2260 60 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

CAL-23M 7992546 444925 Peat 2270 60 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

CAL-115 7989092 447722 Peat 3810 120 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

Socapave Unit

CAL-23A 7992546 444925 Peat 10850 100 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

CAL-23O 7992546 444925 Ash layer withorganic material

10250 90 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosiveactivity of Putre Unit

CAL-11 7988264 442427 Carbonized wood 10170 90 AMS Carbonized wood within blast deposit. Age of pyroclastic activity of Socapave UnitCAL-132 7987768 441308 Palaeo-soil 10832 65 AMS Carbonized wood within blast deposit. Age of pyroclastic activity of Socapave UnitCAL-23B 7992546 444925 Peat 9850 70 Conventional Lacustrine sequence with peat, sediment and tephra fallout layers. Age of explosive

activity of Putre Unit

CAL-130B 7988398 439500 Peat 8380

120 Conventional Peat layer on top of pyroclastic sequence. Minimum age of Socapave UnitTajane UnitCAL-124D 7987788 440673 Palaeo-soil 9110 240 Conventional Date stratigraphically inconsistentCAL-130 7988398 439500 Carbonized wood 24410 180 AMS Carbonized wood within blast deposit in upper part of sequence. Age of pyroclastic

activity of Tajane Unit

*Present is ad 1950.

Fig. 8. (a) Hummocky morphology of the Socapave debris avalanche deposit (black dashed curve shows hummocky surface of the avalanche deposit)

covered by block-and-ash flow, blast and secondary pyroclastic flow deposits of the Socapave and Putre units. Photograph taken 1 km to the east of Putre

village; person for scale. (b) Detail of fracture in the Socapave debris avalanche deposit filled by a blast deposit of the same unit (see text for discussion).

Hammer is 30 cm long.



12/17

and fines-poor, and the upper one being fines-rich. Secondary

(surge-derived; Druitt et al. 2002) pyroclastic flow deposits are

very local, thin (less than 40 cm thick), massive and fine-grained(fine to coarse ash particle size), and commonly infill localdepressions (Fig. 10a).

Rock-fall deposits have been recognized on the northwestern

slopes of the domes (Fig. 3). They consist of an unconsolidatedmonomict breccia talus (with fragments up to 2 m in diameter).

Three 40Ar/39Ar (Table 2) and six radiocarbon (Table 3) dateshave been obtained. The earliest Socapave debris avalanche has

an age of c. 25 ka (Table 2). Two other block-and-ash flowdeposits were dated at c. 20 and 15 ka (Table 2). Six radiocarbondates were obtained within the pyroclastic sequence, ranging

from 9.8 to 10.8 ka (Table 3). These dates constrain the Socapave

Unit between 25 and 9 ka.

Putre Unit (Holocene, ,9 ka). The youngest unit of TaapacaVolcanic Complex covers an area of more than 18 km2 on thecentral, southern and southwestern flanks. It consists of a series of

domes, block-and-ash flow, blast, tephra fallout, primary andsecondary pyroclastic flows, and lahar deposits (Fig. 7). Thesedeposits partially filled the irregular topography of the Socapavedebris avalanche (Fig. 9a) and the gullies developed in the previous

pyroclastic terraces formed by the Socapave and Tajane units.The youngest domes of Taapaca Volcanic Complex crop out

on its eastern and southern borders (Fig. 3). The eastern domes

Fig. 9. (a) Southwestern flank of Taapaca Volcanic Complex viewed from the north. The hummocky topography of the Socapave debris avalanche deposit

has been smoothed and partially filled by Putre Unit pyroclastic deposits forming a flat terrace. ( b) Detail of a block-and-ash flow deposit of the Putre

Unit. It should be noted that a gas segregation pipe is deformed (white arrow) in the flow direction of the overlying blast (note the imbricated clast in the

deposit; see text for discussion). Hammer is 25 cm long.

Fig. 10. (a) Detail of pyroclastic deposits of the Socapave (S) and Putre (P) units (separated by a white dashed curve), 500 m to the east of Putre village.14C date obtained in carbonized wood at the base of a blast deposit (b) is shown. A block-and-ash flow (ba) and a surge-derived pyroclastic flow (spf) can

also be seen in the sequence. The white dashed curve marks the limit between the two units. Person for scale. ( b) Detail of a prismatically jointed block

fragment in a coarse-grained block-and-ash flow deposit of Socapave Unit, near Putre village. Hammer is 30 cm long. ( c) Highly fluidized block-and-ash

flow deposit (with gas segregation pipes), overlain by fine-grained ash-cloud surge deposit (acs), which is overlain itself by thin white co-pyroclastic flow

ash fallout deposit (fa). Lens is 5 cm in diameter. (d) Detail of gas segregation pipes from (c), showing gas pipes surrounding a large block with a fines-

rich upper surface (fr) and fines-depleted areas at the bottom and in the surroundings. Lens is 5 cm in diameter.



13/17

are the largest, having subcircular to elliptical bases (Fig. 6a),whereas the southern ones are smaller (Fig. 6b). They usuallyhave blocky surfaces and have small-volume block-and-ash flowdeposits around their bases.

A pyroclastic sequence, commonly less than 60 m thick, cropsout to the south and SW, infilling deep gullies or covering the

pyroclastic deposits of the Tajane and Socapave units (Figs 7 and

10a).The block-and-ash flow deposits range from up to 30 m to less

than 2 m thick, with dacitic, rounded to subrounded, fragmentsup to 3 m in diameter with common prismatically jointed blocks.Maximum block size decreases with distance to less than 10 cmin distal areas. Common gas segregation pipes (Figs 9b and 10c,d) tend to develop towards the upper part of the deposit (Fig.

9b). Thin layers (usually less than 20 cm thick) of ash-cloudsurge deposits are common on top of the deposit (Fig. 10c).These ash-cloud surge deposits are usually fine-grained, showingwell-developed cross-lamination and dune structures, although

coarser-grained lenses also occur (Fig. 10c). They usuallytruncate the underlying gas segregation pipe structures developedin the upper part of the block-and-ash flow deposits (Fig. 10c),suggesting erosion by the surges.

Blast deposits, which originated by directional dome explo-

sions usually caused by sudden decompression, have been widelydescribed in the literature (Gorshkov & Dubik 1970; Hoblitt etal. 1981; Belousov 1996; Hoblitt et al. 1997; Druitt 1998; Sparks

et al. 2002). These deposits are common in the latest Taapaca

Volcanic Complex eruptive history. Blast deposits are commonlythin (less than 3 m), and show two distinctive layers, similar toother blast deposits related to domes (Hoblitt et al. 1981;Boudon & Lajoie 1989; Druitt 1992; Belousov 1996; Gladstone

& Sparks 2002; Ritchie et al. 2002). The lower layer is generallymassive, fines-poor, and formed by coarse ash to fine lapilli,locally showing thin surge deposits at the base. The upper layeris finer-grained and sometimes shows reverse grading (Fig. 9b).

Sometimes the largest fragments are imbricated, and the over-lying blast deforms pipe structures of the underlying deposits(Fig. 9b), suggesting little or no time-gap between the depositionof the two flows. The blasts are closely related in space and time

with block-and-ash flows, suggesting that most of them origi-nated as a result of sudden decompression during dome collapse,

as has been observed to occur in the Soufriere Hills volcano(Cole et al. 2002; Sparks et al. 2002).

Secondary (surge-derived) pyroclastic flow deposits are locallyexposed, generally infilling palaeochannels with no lateral con-

tinuity, and commonly overlying blast deposits. They consist ofmassive, mainly fine-grained, thin layers (less than 1 m thick)that thin towards the higher parts of the infilled palaeotopogra-

phy. There is neither reworked material nor erosive features at

the sharp contact between the deposits, which suggests that thepyroclastic flow was deposited simultaneously with, or immedi-ately after, the blast. These close relationships suggest that these

pyroclastic flows originated from a parent blast cloud, as hasbeen recently observed to occur in the eruption of the SoufriereHills volcano (Calder et al. 1999; Cole et al. 2002; Druitt et al.2002).

A pumice flow deposit has been recognized on the westernflanks, with a run-out of less than 3.5 km and a maximum

thickness of 10 m. It consists of subrounded rhyodacitic pumicefragments up to 50 cm in diameter, within a fine-grained massivematrix.

Two types of tephra fallout deposits have been observed. One

is preserved in two lake-filled depressions, interbedded with peatand lake sediments, within the hummocky topography of the

Socapave debris avalanche deposit (Fig. 3). These are generallyfine-grained (medium ash to fine lapilli) and well sorted, withthickness ranging between 15 and 50 cm. The other typecorresponds to thin (less than 2 cm) ash layers locally found on

top of ash-cloud surge deposits associated with block-and-ashflow deposits (co-pyroclastic flow ash fallout; Fig. 10c and d).

Lahar deposits have been recognized in the main eastern andsouthern valleys of Taapaca Volcanic Complex, covering small

areas and reaching 5 km from their source (Fig. 3). They consist

of unconsolidated polymict breccias with angular fragments upto 2 m in diameter, within a sandy matrix, which shows poorly

developed flow-parallel bedding.Nine radiocarbon dates were obtained from this unit (Table 3).

Two of them give the age of the pyroclastic deposits, as they

were obtained from carbonized wood within a blast layer andfrom an organic-rich ash fallout layer, showing that TaapacaVolcanic Complex has produced at least three block-and-ashflows younger than 8 ka. The rest give a relative age of tephra

fallout deposits as they were obtained from organic-rich sedi-ments between the volcanic deposits, showing that tephra fallout,

probably formed by ash-venting, possibly related to domeactivity, occurred between 7 and 2 ka bp.

Discussion

The volcanic evolution and stratigraphy of Taapaca Volcanic

Complex has important implications for the evolution and behav-iour of Andean dome complex volcanoes, for the assessment ofvolcanic hazards of one of the most populated areas of theChilean Altiplano, and for the Late Quaternary history of this

part of the Central Andes.

Volcanic evolution of Taapaca Volcanic Complex

During its first stage (,1.5 Ma) Taapaca Volcanic Complexstarted to build with the effusion of high-K silicic andesite (Fig.4) lavas and the formation of a gently dipping shield-like

stratovolcano in the northern part of the complex, with the mainfocus of eruptive activity probably located in the area marked T1in Figure 11.

During Stage II, high-K dacite magmas (Fig. 4), characterizedby mafic inclusions and sanidine megacrysts, started to emerge,generating thick dacitic lava flows, domes and a pyroclastic fan.A large (c. 6080 km3), steeply dipping dacitic lava-dome

complex (Fig. 5b) with its associated pyroclastic fan was thenformed. The main vent system was probably located in the areamarked T2 in Figure 11, which represents a migration of 1.5

2 km to the SSW of the Stage I centre.During Stage III a series of high-K dacite (Fig. 4) domes and

associated pyroclastic deposits were erupted, forming a domecomplex in the southern part of the ancestral stratocone (Figs 3

and 11). The eruptive activity was mainly concentrated in thewestern part of the complex and on the eastern side along anorthsouth fracture, showing that the main focus of eruptiveactivity continued to migrate towards the south, about 12 km

from the ancestral Stage II stratocone (T3 in Fig. 11).During the latest stages of Stage II, and probably during Stage

III, extensive glacial erosion affected the ancestral edifice, asevidenced by glacial deposits. A third of the original edifice(Stages II and III) was removed, mainly from the southern part,leaving exposed a hydrothermally altered core (Fig. 5b). A major

sector collapse of the southern part of the complex at thebeginning of Stage IV also contributed to its deep dissection.

During Stage IV a dome complex developed on the southern



14/17

part of the complex, showing that the main focus of eruptiveactivity continued to migrate towards the SSW about 1.52 km

from the Stage III focus, and over a total of 45 km since StageI (T4 in Fig. 11). A series of voluminous dacitic domes wasformed and associated recurrent pyroclastic and debris flowactivities were mainly directed towards the south and SW (Fig.

3). Extensive pyroclastic terraces formed during these explosivephases in the last 40 ka, constantly changing the topography,especially in the surroundings of Putre village. Magma composi-

tion did not vary from Stages II and III, although both maficinclusion and sanidine megacryst content increased.

Late PleistoceneHolocene dome growth collapseactivity

Several dome eruptions have occurred in the last century aroundthe world, which have strongly affected the surrounding popula-tions and environments (Lacroix 1903; Christiansen & Peterson

1981; Nakada et al. 1999; Sparks & Young 2002). However, inrecent years the development of new monitoring techniques hasimproved understanding of eruption processes. Especially signifi-cant have been the recent eruptions of Mount St. Helens, USA,

in 1980 (Lipman & Mulineaux 1981); Pinatubo, Philippines, in1991 (Newhall & Punongbayan 1997); Unzen, Japan, in 19901995 (Nakada et al. 1999); and Soufriere Hills, Montserrat, in19951999 (Sparks & Young 2002). Late Pleistocene to Holo-

cene eruptive activity in the Taapaca Volcanic Complex has beencharacterized by repetitive periods of dome growth. Each dome

growth phase has itself produced repetitive periods of collapse,ash venting and pyroclastic flows, which were emplaced in short

periods of time (no erosive gaps and local preservation ofsecondary pyroclastic flow and co-pyroclastic flow fallout depos-

its). These periods of eruptive activity were separated byrelatively short periods of quiescence, and therefore of erosion.

Domes formed during the Taapaca Volcanic Complex eruptive

history have steep slopes, different shapes and dimensions (Table4), and some have preserved shear zones similar to those

observed in recent domes (Watts et al. 2002).Debris avalanches of two types formed during Stage IV.

Churilinco debris avalanche formed by the failure of a weak,strongly altered edifice. This extensive alteration may have

caused its instability. The triggering mechanism of the sectorcollapse is not yet clear. However, no evidence of hot emplace-ment and thus of magmatic triggering has been found, supportingthe hypothesis that weakening of the edifice by hydrothermal

alteration was its main cause, as has been suggested for othervolcanic centres (Lopez & Williams 1993). Recently, a major

flank collapse of hydrothermally altered rocks occurred atSoufriere Hills, Montserrat, generating a debris avalanche(Sparks et al. 2002; Voight et al. 2002). The other type of debrisavalanche is that formed by a sector collapse induced by the

intrusion of a cryptodome. The Socapave debris avalanche is anexample of this type. The occurrence of a blast deposit, whichinfills fractures in the avalanche deposit as well as beingincorporated into the avalanche deposit itself, indicates that

sector collapse triggered the blast. At the same time theoccurrence of the blast immediately after the collapse suggeststhat the collapse was itself triggered by deformation of the

edifice caused by magma ascent into the edifice, as has beenobserved and documented in several dome eruptions (Hoblitt etal. 1981; Druitt 1992; Belousov 1996).

Block-and-ash flows were formed by the collapse of an

unstable lava dome (Merapi-type). This type of flow is commonin dome eruptions (Williams & McBirney 1979; Calder 1999;

Calder et al. 1999; Ui et al. 1999; Druitt et al. 2002). TaapacaVolcanic Complex block-and-ash flows have long run-outs, withdeposits reaching 13 km from their probable source (Fig. 3). Thisdistance is as much as twice the run-out of the same type of

flows from Soufriere Hills volcano (Calder 1999; Calder et al.1999) and from Unzen volcano (Ui et al. 1999). Although

Fig. 11. Sketch map showing the migration

of the main focus of eruptive activity

through time (T1T4, for Stages IIV).



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individual volume estimates for the block-and-ash flow depositsare difficult, the volumes should be related to the volume of the

domes (Table 4). Although many of Taapaca Volcanic Complexdomes have similar volumes to those erupted at Soufriere Hillsand Unzen, some of them have much larger volumes (Table 4),

up to 20 times the largest flow deposit from Soufriere Hills(Calder et al. 1999). Following the idea that flow run-outs aredirectly related to the flow volume (Hsu 1975; Dade & Huppert

1998; Calder et al. 1999), the Taapaca Volcanic Complex longerblock-and-ash flow run-outs could be the result of larger volumecollapses than those that occurred in Montserrat and at Unzen.

Pyroclastic flows generated by collapse of an eruptive column,and secondary pyroclastic flows formed by rapid sedimentationfrom a dilute blast, have also been recognized at TaapacaVolcanic Complex. Only one pumice-rich deposit generated by a

column-collapse flow has been identified. This flow has the mostevolved juvenile material from Stage IV. This fact might help to

explain its occurrence in a dome complex where subplinianexplosive columns are not common, and where most of theexplosive activity is directly related to dome growthcollapseexplosion. The final type corresponds to secondary pyroclastic

flow deposits, interpreted to have formed by sedimentation fromprimary coarser blast flows (Druitt et al. 2002).

Two main types of pyroclastic surges occurred at TaapacaVolcanic Complex. Volcanic blasts occurred immediately after

sector collapses. These blasts probably originated, as discussed

above, by sudden depressurization of cryptodomes after sectorcollapse. Most common are ash-cloud surge deposits, which arefound on top of block-and-ash flow deposits. They probablyrepresent the deposit of the overlying ash cloud of the main body,which entrapped some air and then became more dilute than its

parent flow, as suggested by Fujii & Nakada (1999). However,sometimes ash-cloud surges from the Taapaca Volcanic Complexcrop out in areas where no block-and-ash flow deposits are

present. This is believed to happen when the overlying surge

cloud detached from the main body of a flow, as has beenobserved during the eruptions of Unzen (Fujii & Nakada 1999)and Soufriere Hills (Cole et al. 2002).

Tephra fallout deposits are not widely recognized. This could

be due either to lack of preservation caused by erosion or to the

fact that Taapaca Volcanic Complex has not produced higheruptive columns. Only two types have been recognized. Thin

ash fallout layers are preserved only in palaeobasins within theSocapave debris avalanche deposit. Their distribution, particle

size and thickness suggest that they represent periods of ashventing related to dome growth. The other type corresponds tolocalized, extremely thin and fine-grained deposits, which areinterpreted as co-pyroclastic flow fallout in the sense of

Bonadonna et al. (2002), associated with block-and-ash flows.The local preservation of these easily erodable deposits suggeststhat the overlying flows were emplaced soon afterwards.

Volcanic hazards

Taapaca Volcanic Complex has been historically inactive. How-ever, in this part of the Central Andes the Spanish arrived in thearea only c. 450 years ago. The new data indicate that Taapaca

Volcanic Complex is a dormant volcano, with a potential forfuture eruptions. According to the spatial distribution of the LatePleistoceneHolocene domes and deposits, it is likely that, in thecase of renewed activity, products will be distributed over the

southern and southwestern flanks of the complex. An injection ofa new pulse of magma would cause deformation of the edifice,result in instability, and trigger a partial collapse of the upper

flanks and domes with a debris avalanche directed towards theSSW. This sequence of events has been recurrent in Stage IV, aswell as in other intermediate volcanoes and dome complexes(Beget & Kienle 1992; Siebert et al. 1995; Ponomareva et al.

1998; Belousov et al. 1999). The three main debris avalanchedeposits recognized so far (Churilinco, Tajane and Socapavedebris avalanches) have flowed down to the SSW, and two ofthem have reached the area where the village of Putre has been

built. There are likely to be associated volcanic blasts, asexperienced at Mount St. Helens (Hoblitt et al. 1981) and

Soufriere Hills (Sparks et al . 2002). In the case of domeextrusion, explosions, dome collapses and pyroclastic flows will

be generated, as has also been a recurrent phenomenon in theStage IV eruptive history as well as at other dome eruptions

worldwide (Nakada et al. 1999; Ui et al. 1999; Robertson et al.2000; Druitt et al. 2002; Sparks & Young 2002). Some flows will

probably reach the Putre village area and the busiest international

Table 4. Volume estimates from selected domes, lava-domes and lavaflows from Taapaca Volcanic Complex

Type Basal shape L1(km)

L2(km)

H(km)

Basal area(km2)

Volume(km3)

Stage IV

Putre UnitDome Elliptical 0.36 0.92 0.15 1.04 0.08Dome Elliptical 0.36 0.68 0.15 0.77 0.06Dome Elliptical 0.72 1.20 0.25 2.71 0.34

Dome Subcircular 1.04 1.04 0.35 0.85 0.17Dome Subcircular 0.52 0.52 0.25 0.21 0.03Dome Subcircular 0.72 0.80 0.30 0.41 0.08Dome Subcircular 0.60 0.52 0.25 0.28 0.04Dome Subcircular 0.48 0.60 0.30 0.18 0.04Socapave UnitDome Elliptical 0.72 1.12 0.06 2.53 0.08Dome Elliptical 0.72 1.00 0.20 2.26 0.23Dome Elliptical 0.44 0.76 0.20 1.05 0.11Dome Elliptical 1.60 1.28 0.30 6.43 0.97Dome Elliptical 1.20 0.32 0.12 1.21 0.07Tajane UnitDome Subcircular 0.72 0.60 0.15 0.41 0.03Lava-dome Sheet-like 1.84 0.60 0.10 1.10 0.11Lava-dome Sheet-like 3.00 0.80 0.10 2.40 0.24Churilinco

UnitLava-dome Sheet-like 0.84 2.40 0.12 2.02 0.24Stage III

Dome Elliptical 0.52 1.52 0.20 2.48 0.25Dome Subcircular 0.84 0.84 0.28 0.55 0.09Dome Elliptical 0.64 2.40 0.18 4.83 0.43Dome Subcircular 0.68 0.72 0.20 0.36 0.04Dome Sheet-like 1.20 1.56 0.20 1.87 0.37Dome Elliptical 0.68 0.40 0.10 0.85 0.04Lava-dome Sheet-like 2.40 1.08 0.15 2.59 0.39Lava-dome Sheet-like 0.64 1.92 0.10 1.23 0.12Lava-dome Sheet-like 0.80 1.60 0.10 1.28 0.13Lava-dome Sheet-like 0.80 0.80 0.10 0.64 0.06Stage II

Dome Subcircular 0.84 0.84 0.25 0.55 0.08Dome Elliptical 0.44 0.96 0.20 1.33 0.13Dome Subcircular 0.48 0.48 0.15 0.18 0.02

Lava-dome Sheet-like 3.20 1.40 0.15 4.48 0.67Lava-dome Sheet-like 1.20 2.24 0.15 2.69 0.40Lava-dome Sheet-like 1.60 2.80 0.15 4.48 0.67Lava-dome Sheet-like 1.60 2.00 0.15 3.20 0.48Stage I

Lava flow Sheet-like 2.32 4.00 0.06 9.28 0.56Lava flow Sheet-like 2.12 4.40 0.07 9.33 0.65



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road connecting Chile and Bolivia (Figs 2 and 3). Secondary(surge-derived) pyroclastic flows are documented in the Andesfor the first time. Such flows can easily detach from their originalsurge source and move in a completely different direction

(Calderet al. 1999; Druitt et al. 2002).Lahars are likely to be generated and two possible situations

are envisaged. A first case might occur if an eruption develops

between the months of April and November, when there is aprominent snow-cap in the upper part of the complex. Lahar

flows will develop and probably be confined to the main valleysand gullies on the south and southwestern flanks of the complex.Depending on their extension (volume) they could reach both theinternational road and the outskirts of Putre. Other flows couldalso be directed to the western flank, affecting the main road that

connects Putre with the northernmost villages in the ChileanAltiplano (Fig. 2). A second situation, not directly associatedwith new volcanic activity, could develop during the rainyseason, from December to March. Small-volume rain-induced

lahars occur each year, as a result of the remobilization of loosevolcaniclastic material from the steep slopes of the complex.Although they rarely reach populated areas, they commonly cutroads. However, if an eruption occurs the availability of loose

material would increase and therefore the volume of these flows

would also increase, favouring greater runout lengths.Finally, from a statistical analysis of Taapaca Volcanic Com-plex eruptive activity in the last 30 ka (Abramowitz & Stegun1970; De la Cruz 1996), it is possible to say that it has had an

eruption rate of 1.6 eruptions per thousand years, with aneruption recurrence of 450 years (95% confidence interval). Asthe eruptions follow a Poisson distribution, the occurrence

probability of an eruption in the next 100 years can be estimated

at 15%, and in the next 500 years at 56% (De la Cruz 1996).Considering its late Quaternary eruptive history and composition,another eruption can be expected to last several years or evendecades, as has been the case for Unzen, Japan (Nakada & Fujii

1993; Nakada et al. 1999), Soufriere Hills, Montserrat (Voight etal. 1999; Robertson et al. 2000; Sparks & Young 2002) andSantiaguito, Guatemala (Rose 1973, 1987).

Conclusions

Taapaca Volcanic Complex is a long-lived volcanic complex ofthe Central Andes, which started its eruptive activity at around1.5 Ma, forming a gently dipping stratocone of andesitic lava

flows (Stage I). It later evolved to a voluminous steep-sidedstratocone, formed by sanidine megacryst-bearing dacitic lavaflows, domes and block-and-ash flow deposits (Stage II). This

morphological and geochemical evolution was accompanied by aslight migration of the main focus of eruptive activity towardsthe SSW. This migration continued during Stage III, when adome complex to the south of the ancestral Stage II stratocone,

as well as a dome complex aligned in northsouth direction inthe eastern part of the old edifice, were built. The magmaerupted did not change in composition, but a slight increase inmafic inclusion and sanidine megacryst contents occurred. A

huge pyroclastic fan to the west of the complex was formed,reaching distances of more than 13 km from its source. During

its latest evolution stage, of Late PleistoceneHolocene age, adome complex to the south of Stage III dome complex wasformed, showing that the migration of the main focus of eruptiveactivity has continued towards the SW. The composition of the

magma erupted during Stage IV has not changed; only a slightincrease in both mafic inclusion and sanidine megacryst contentis observed. The Late PleistoceneHolocene activity has been

characterized by the extrusion of several voluminous daciticdomes and the occurrence of numerous block-and-ash flows,

blasts, fallouts, lahars and both primary and secondary pyroclas-tic flows mainly directed towards the southern flank of the

complex, forming long fans that reach more than 13 km fromtheir source. Most of the Holocene activity has been directedtowards the SW, where is located the most populated area of theChilean Altiplano and its main town, Putre. This poses a serious

threat to human activity in the area, given that new eruptions are

likely in Taapaca Volcanic Complex in the next decades orcenturies.

This work has been funded through a collaborative project between

SernageominChile and University of Bristol, UK. J.E.C. acknowledges

the support of Pdte de la Republica Scholarship (Mideplan Chile) and

R.S.J.S. acknowledges an NERC Professorship. Radiocarbon dates were

obtained through a collaborative project between SernageominChile and

GSC, Canada. 40Ar/39Ar dates were obtained through an NERC grant (to

R.S.J.S. and M.S.P.). The authors gratefully acknowledge O. Roche, A.

Daz, J. Lemp and M. Robles for their help in the field. C. Espejo, F.

Llona, J. Imlach and B. Davidson provided technical assistance in

obtaining geochemical and geochronological data. S. Self and C. Kilburn

provided thorough and very helpful reviews, which helped to improve the

manuscript. We also would like to thank M. Fowler for his help and

patience.

References

Abramowitz, M. & Stegun, I.A. 1970. Handbook of Mathematical Functions.

Dover Book on Advanced Mathematics. Dover, New York.

Beget, J. & Kienle, J. 1992. Cyclic formation of debris avalanches at Mt. St.

Augustine volcano, Alaska. Nature, 356, 701704.

Belousov, A. 1996. Deposits of the 30 March 1956 directed blast at Bezymianny

Volcano, Russia. Bulletin of Volcanology, 57, 649662.

Belousov, A., Belousova, M. & Voight, B. 1999. Multiple edifice failures,

debris avalanches and associated eruptions in the Holocene history of

Shiveluch volcano, Kamchatka, Russia. Bulletin of Volcanology, 61, 324342.

Bonadonna, C., Macedonio, G. & Sparks, S. 2002. Numerical modelling of

tephra fallout associated with dome collapses and Vulcanian explosions:

applications to hazard assessment on Montserrat. In: Druitt, T. &

Kokelaar, P. (eds) The Eruption of Soufriere Hills Volcano, Montserrat,from 1995 to 1999. Geological Society, London, Memoirs, 21, 517538.

Boudon, G. & Lajoie, J. 1989. The 1902 Peleean deposits of the Fort Cemetery of

St. Pierre, Martiniquea model for the accumulation of turbulent nuee-

ardentes. Journal of Volcanology and Geothermal Research, 38, 113129.

Calder, E. 1999. Dynamics of small to intermediate volume pyroclastic flows . PhD

thesis, University of Bristol.

Calder, E., Cole, P. & Dade, B. et al. 1999. Mobility of pyroclastic flows and

surges at the Soufriere Hills Volcano, Montserrat. Geophysical Research

Letters, 26(5), 537540.

Christiansen, R. & Peterson, D. 1981. Chronology of the 1980 eruptive activity.

In: Lipman, P. & Mulineaux, D. (eds) The 1980 Eruptions of Mount St.

Helens, Washington. US Geological Survey, Professional Papers, 1250,

1730.

Clavero, J. 2002. Evolution of Parinacota Volcano and Taapaca Volcanic

Complex, Central Andes of Northern Chile. PhD thesis, University of Bristol.

Clavero, J., Sparks, S., Huppert, H. & Dade, B. 2002. Geological constraints on

the emplacement mechanism of the Parinacota debris avalanche, Northern

Chile. Bulletin of Volcanology, 64(1), 4054.Cole, P., Calder, E. & Sparks, S. et al. 2002. Deposits from dome-collapse and

fountain collapse pyroclastic flows at Soufriere Hills Volcano, Montserrat. In:

Druitt, T. & Kokelaar, P. (eds) The Eruption of Soufriere Hills Volcano,

Montserrat, from 1995 to 1999. Geological Society, London, Memoirs, 21,

231262.

Dade, W. & Huppert, H.E. 1998. Long run-out rockfalls. Geology, 26, 803806.

Dalrymple, B. & Duffield, W. 1988. High-precision Ar-40/Ar-39 dating of

Oligocene rhyolites from the MogollonDatil volcanic field using a continous

laser system. Geophysical Research Letters, 15(5), 463466.

De la Cruz, S. 1996. Long-term probabilistic analysis of future explosive

eruptions. In: Scarpa, R. & Tilling, R. (eds) Monitoring and Mitigation of

Volcanic Hazard. Springer, Berlin, 599629.

de Silva, S. & Francis, P. 1991. Volcanoes of the Central Andes. Springer, Berlin.

Druitt, T. 1992. Emplacement of the 18 May 1980 lateral blast deposit east-



17/17

northeast of Mount St. Helens, Washington. Bulletin of Volcanology, 54,

554572.

Druitt, T. 1998. Pyroclastic density currents. In: Gilbert, J. & Sparks, S. (eds)

The Physics of Explosive Volcanic Eruptions. Geological Society, London,

Special Publications, 145, 145182.

Druitt, T., Calder, E. & Cole, P. et al. 2002. Small-volume, highly mobile

pyroclastic flows by rapid sedimentation from pyroclastic surges at Soufriere

Hills volcano, Montserrat: an important volcanic hazard. In: Druitt, T. &

Kokelaar, P. (eds) The Eruption of Soufriere Hills Volcano, Montserrat,

from 1995 to 1999. Geological Society, London, Memoirs, 21, 263280.

Fujii, T. & Nakada, S. 1999. The 15 September 1991 pyroclastic flows at Unzen

Volcano (Japan): a flow model for associated ash-cloud surges. Journal ofVolcanology and Geothermal Research, 89, 159172.

Garca, M. 2001. Evolution oligo-neogene de larc et de lavant-arc de lAltiplano

(Andes Centrales, Coude dArica, 18198S). Tectonique, volcanisme, sedi-

mentation, geomorphologie et bilan erosionsedimentation. PhD thesis,

Universite Joseph Fourrier, France.

Garca, M., Gardeweg, M., Clavero, J. & Herail, G. 2004. Mapa Geologico de

la Hoja Arica, 1:250000 scale. Servicio Nacional de Geologa y Minera,

Chile.

Gardeweg, M., Sparks, S. & Matthews, S. 1998. Evolution of Lascar Volcano,

Northern Chile. Journal of the Geological Society, London, 155, 89104.

Gladstone, C. & Sparks, S. 2002. The significance of grain-size breaks in

turbidites and pyroclastic density current deposits. Journal of Sedimentary

Research, 72(1), 182191.

Gonzalez, O. 1995. Volcanes de Chile. Instituto Geografico Militar, Santiago.

Gorshkov, G. & Dubik, Y. 1970. Directed volcanic blasts at Shiveluch Volcano

(Kamchatka). Bulletin Volcanologique, 34, 262288.

Harford, C. 2001. The volcanic evolution of Montserrat. PhD thesis, University of

Bristol.

Harford, C., Pringle, M., Sparks, S. & Young, S. 2002. The volcanic evolution

of Montserrat using 40Ar/39Ar geochronology. In: Druitt, T. & Kokelaar,

P. (eds) The Eruption of Soufriere Hills Volcano, Montserrat, from 1995 to

1999. Geological Society, London, Memoirs, 21, 93113.

Hoblitt, R., Miller, D. & Vallance, J. 1981. Origin and stratigraphy of the

deposit produced by the May 18 directed blast. In: Lipman, P. &

Mulineaux, D. (eds) The 1980 Eruptions of Mount St. Helens, Washington .

US Geological Survey, Professional Papers, 1250, 401419.

Hoblitt, R., Wolfe, E., Scott, W., Coughman, M., Pallister, J. & Javier, D.

1997. The pre-climactic eruptions of Mount Pinatubo, June 1991. In:

Newhall, C. & Punongbayan, R. (eds) Fire and Mud: Eruptions and

Lahars of Mount Pinatubo, Philippines. University of Washington Press,

Seattle, 457511.

Hsu, K.J. 1975. On strurzstromscatastrophic debris streams generated by

rockfalls. Geological Society of America Bulletin, 86, 129140.

Kohlbach, I. & Lohnert, E. 1999. Geological map of Taapaca Volcano and

adjacent areas (North Chile), 1:25000. Thesis, Universitat zu Gottingen,Germany.

Lacroix, J. 1903. La Mo ntagne Pelee et ses erupt ions. Masson, Paris.

Lipman, P. & Mulineaux, D. (eds) 1981. The 1980 Eruptions of Mount St.

Helens, Washington. US Geological Survey, Professional Papers, 1250.

Lohnert, E. 1999. Chemical variations of sanidine megacryst and its implications

on the pre-eruptive evolution of the Taapaca volcano in North Chile: electron

microprobe and Sr-isotope studies. Thesis, Universitat Got tingen, Germany.

Lopez, D. & Williams, S. 1993. Catastrophic volcanic collapse: relation to

hydrothermal processes. Science, 260, 17941796.

Maniken, E. & Dalrymple, G. 1972. The electron microprobe and KAr dating.

Earth and Planetary Science Letters, 17, 8994.

Montecinos, F. 1963. Observaciones de geologa en el Cuadrangulo de

Campanani, Departamento de Arica, Provincia de Tarapaca. Thesis, Uni-

versity of Chile.

Munoz, N. & Charrier, R. 1996. Uplift of the western border of the Altiplano on

a west-vergent thrust system, Northern Chile. Journal of South American

Earth Sciences, 9(3/4), 171181.

Munoz, N. & Sepulveda, P. 1992. Estructuras compresivas con vergencia alOeste en el borde oriental de la Depresion Central, Norte de Chile (19815lat.

S). Revista Geologica de Chile, 19(2), 241247.

Nakada, S., Shimizu, H. & Ohta, K. 1999. Overview of 19901995 eruption at

Unzen volcano. Journal of Volcanology and Geothermal Research, 89, 122.

Newhall, C. & Punongbayan, R. (eds) 1997. Fire and Mud: Eruptions and

Lahars of Mount Pinatubo, Philippines. University of Washington Press,

Seattle.

Pacci, D., Herve, F., Munizaga, F., Kawashita, K. & Cordani, U. 1980.

Acerca de la edad Rb/Sr precambrica de rocas de la Formacion Esquistos de

Belen . Departamento de Parinacota, Chile. Revista Geologica de Chile, 11,

2329.

Ponomareva, V., Pevzner, M. & Melekestsev, I. 1998. Large debris avalanches

and associated eruptions in the Holocene eruptive history of Shiveluch

Volcano, Kamchatka, Russia. Bulletin of Volcanology, 59, 490505.

Ritchie, L., Cole, P. & Sparks, S. 2002. Sedimentology of deposits from the

pyroclastic density currents of 26 December (Boxing Day) 1997 at Soufriere

Hills Volcano, Montserrat. In: Druitt, T. & Kokelaar, P. (eds) The

Eruption of Soufriere Hills Volcano, Montserrat, from 1995 to 1999.

Geological Society, London, Memoirs, 21, 435456.

Robertson, R., Aspinall, W., Herd, R., Norton, G., Sparks, S. & Young, S.

2000. The 19951998 eruption of the Soufriere Hills volcano, Montserrat,

WI. Philosophical Transactions of the Royal Society of London, 358,16191637.

Rose, W. 1973. Pattern and mechanism of volcanic activity at the Santiaguito

Volcanic Dome, Guatemala. Bulletin Volcanologique, 37, 7394.

Rose, W. 1987. Volcanic activity at Santiaguito volcano. In: Fink, J. (ed.) The

Emplacement of Silicic Domes and Lava Flows. US Geological Survey,

Special Papers, 212, 1727.

Salas, R., Kast, R., Montecinos, F. & Salas, I. 1966. Geologa y recursos

minerals del Departamento de Arica, Provincia de Tarapaca. Instituto de

Investigaciones Geologicas Bulletin, 21, 1130.

Siebert, L., Beget, J. & Glicken, H. 1995. The 1883 and late-prehistoric

eruptions of Augustine volcano, Alaska. Journal of Volcanology and

Geothermal Research, 66, 367395.

Sparks, S. & Young, S. 2002. The eruption of Soufriere Hills Volcano, Montserrat

(19951999): overview of scientific results. In: Druitt, T. & Kokelaar, P.

(eds) The Eruption of Soufriere Hills Volcano, Montserrat, from 1995 to 1999.

Geological Society, London, Memoirs, 21, 4570.

Sparks, S., Barclay, J. & Calder, E. e t al. 2002. Generation of a debris

avalanche and violent pyroclastic density current on 26 December 1997

(Boxing Day) at Soufriere Hills Volcano, Montserrat. In: Druitt, T. &

Kokelaar, P. (eds) The Eruption of Soufriere Hills Volcano, Montserrat,

from 1995 to 1999 . Geological Society, London, Memoirs, 21, 409434.

Steiger, R. & Jager, E. 1977. Subcommission on geochronology: convention on

the use of decay constants in geo- and cosmochronology. Earth and Planetary

Science Letters, 36, 359362.

Taylor, J. 1982. An Introduction to Error Analysis. University Science Books,

Mill Valley, CA.

Torres, R., Self, S. & Martnez, M. 1997. Secondary pyroclastic flows from the

June 15, 1991, igimbrite of Mount Pinatubo. In: Newhall, C. &

Punongbayan, R. (eds) Fire and Mud: Eruptions and Lahars of Mount

Pinatubo, Philippines. University of Washington Press, Seattle, 15, 665678.

Ui, T., Matsuwo, N., Sumita, M. & Fujinawa, A. 1999. Generation of block and

ash flows during the 19901995 eruption of Unzen Volcano, Japan. Journal

of Volcanology and Geothermal Research, 89, 123137.

Voight, B., Sparks, S. & Miller, D. et al. 1999. Magma flow instability and

cyclic activity at Soufriere Hills Volcano, Montserrat, British West Indies.Science, 283, 11381142.

Voight, B., Komorowski, J. & Norton, G. e t al. 2002. The 26 December

(Boxing Day) 1997 sector collapse and debris avalanche at Soufriere Hills

Volcano, Montserrat. In: Druitt, T. & Kokelaar, P. (eds) The Eruption of

Soufriere Hills Volcano, Montserrat, from 1995 to 1999 . Geological Society,

London, Memoirs, 21, 363408.

Watts, R., de Silva, S., Jimenez de Rios, G. & Croudace, I. 1999. Effusive of

viscous silicic magma triggered and driven by recharge: a case study of the

Cerro Chascon Runtu Jarita Dome Complex in Southwest Bolivia. Bulletin

of Volcanology, 60, 241264.

Watts, R., Herd, R., Sparks, S. & Young, S. 2002. Growth patterns and

emplacement of the andesitic lava dome at Soufriere Hills Volcano,

Montserrat. In: Druitt, T. & Kokelaar, P. (eds) The Erup tion of Sou friere

Hills Volcano, Montserrat, from 1995 to 1999. Geological Society, London,

Memoirs, 21, 115152.

Williams, H. & McBirney, M. 1979. Volcanology. Freeman, Cooper, San

Francisco, CA.

Worner, G., Hammerschmidt, K., Henjes-Kunst, F., Lzaun, J. & Wilke, H.2000a. Geochronology (40Ar/39Ar, K Ar and He-exposure ages) of Cen-

ozoic magmatic rocks from northern Chile (18228S): implications for

magmatism and tectonic evolution of the central Andes. Revista Geologica de

Chile, 27(2), 205240.

Worner, G., Lezaun, J. & Beck, A. e t al. 2000b. Precambrian and Early

Paleozoic evolution of the Andean basement at Belen (northern Chile) and

Cerro Uyarani (western Bolivia Altiplano). Journal of South American Earth

Sciences, 13, 717737.

York, D. 1969. Least squares fitting of a straight line with correlated errors. Earth

and Planetary Science Letters, 5, 320324.

Received 9 May 2002; revised typescript accepted 1 February 2004.

Scientific editing by Mike Fowler


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