6GEO4 Unit 4 Tectonic Activity and Hazards

What is this option about?

• The Tectonic Activity and Hazards option focuses on the range of natural hazards generated by plate tectonics

• In addition to understanding why these hazards happen, you will need to understand:

• The impact of tectonic processes on the landscape

• The impact of tectonic hazards on people

• The ways in which people respond to, and try to manage, natural hazards.

Primary hazards

Secondary hazards

Earthquakes Tsunami LandslidesLiquefaction

Volcanoes Lahars Landslides Tsunami

1. Tectonic activity and causes2. Tectonic hazards physical impacts 3. Tectonic hazards human impacts4. Response to tectonic hazards

CONTENTS

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1. Tectonic activity and causes

• Tectonic activity can produce a very large range of hazard events

• Not all of these events are ‘disasters’

• A natural hazard event becomes a disaster when the event causes a significant impact on a vulnerable population.

• These impacts could be human (death, injury) and / or economic (property losses, loss of income).

• Definitions vary, but ‘significant’ losses usually means 10+ deaths / 100+ affected / $1 million losses.

The Dregg disaster model

Event profiles • Not all tectonic hazards are the same• Event profiles are a common way of comparing different

hazards• In this example the 2004 Asian Tsunami and ongoing

eruption of Kilauea on Hawaii are compared • Hazard profiles can be drawn for any event.

Earth’s heat engine

• Tectonic processes are driven by radioactive decay in the core

• This decay generates heat inside the earth, which drives vast convection currents

• This convection is largely responsible for plate movement

Tectonic settings and plates

• Most tectonic hazards are concentrated at plate margins (boundaries), although ‘hotspots’ are a notable exception.

• Different types of boundary generate very different tectonic hazards.

The range of volcanic hazards

• Dangerous volcanic hazards are found along subduction zones at destructive plate margins

• The most dangerous volcanoes are themselves multiple hazard areas.

• Volcanoes at constructive plate margins (Iceland) and oceanic hotspots(Hawaii) are much less hazardous and destructive.

Magma generation

Magma type

Generation Tectonic setting Hazards

BasalticLow silica, low gas, low

viscosity.

Dry partial melting of upper mantle

Oceanic Hot spot (Hawaii)Constructive (Iceland)

Lava flow

Andesitic

Intermediate

Wet partial melting of subducting plates

Destructive plate margin (Andes)Island arc margin (Montserrat)

Lava flow, ash and tephra, pyroclastic flow, lahar, gas emission

RhyoliticHigh silica, high gas, high

viscosity.

In situ melting of lower continental crust(very rare eruptions)

Continental Hot spot (Yellowstone)Continent collision zone (Himalayas)

Cataclysmic explosion, pyroclastic flow

• Magma, molten rock in the earth’s crust, has an important relationship with volcanic explosivity and hazard level

• Andesitic magmas, formed by wet partial melting at subduction zones produce highly explosive and destructive composite volcanoes

Measuring volcanic explosivity:

• The Volcanic Explosivity Index (VEI) is used to measure volcanic power.

• VEI measures: Volume of ejecta Height of the eruption column Duration of the eruption.

• Modern humans have never experienced a VEI 7 or 8

Earthquakes

• Earthquakes are a very common, sudden release of energy that generate seismic waves

• Most occur along faults (cracks in the earth’s crust) which become ‘locked’

• Opposing tectonic forces push against the locked fault, building up strain, which eventually gives way releasing stored energy

• This energy spreads out rapidly from the earthquake origin (the focus) reaching the surface at the epicentre, and then spreading horizontally.

Tsunami

• Tsunami are relatively rare events.• They are generated by submarine earthquakes, volcanic collapse, and

coastal landslides, which suddenly displace huge volumes of water• The 1993 Okushiri tsunami (Japan), 2004 Asian Tsunami and 2009

Samoa events are all useful as case studies. • Tsunami waves are radically different from normal wind generated

ocean waves.• When a tsunami hits a coastline, the effect is more like a devastating

coastal flood than a single breaking waves

2. Tectonic hazards physical impacts

• Tectonic processes play a key role in forming the landscape around us

• Volcanic activity and the movement of tectonic plates create mountains, plateaux and other landscape features

• These landscapes are then modified by geomorphological processes (weathering, rivers, ice, wind and slope processes)

Magma type and volcano morphology

• Volcanoes are extrusive igneous landforms. The form of volcanoes is related to magma types, and therefore to different tectonic settings:

• Basaltic – huge, low relief shield volcanoes plus small scoria cones and fissure vents.

• Andesitic – steep sided strato-volcanoes; layers of lava, ash and tephra.

• Rhyolitic – central craters with lava plugs / domes, due to high viscosity of the lava. Calderas and collapse calderas.

Extrusive igneous activity

• Large scale outpourings of basaltic magma, called flood basalts, have occurred at various times in the past.

• These produce distinctive lava plateaux and stepped or ‘trap’ topography

Intrusive igneous activity

• The injection (intrusion) of magma below the surface can produce characteristic landforms

• Igneous rock normally resists weathering and erosion in comparison to surrounding rocks, which produces positive relief features.

• Large intrusions such as batholiths produce upland areas, whereas minor intrusions produce smaller landscape features

Earthquakes and faults

• Tectonic movements and movements along faults (which generate earthquakes) also produce distinctive landforms and relief:

Note: diagram not to scale

3. Tectonic hazards human impacts

• A surprising number of people live in areas of active tectonic processes

• Major tectonic hazards can strike with devastating force

• The 2005 Kashmir Earthquakes killed around 85000, the 2008 Sichuan ‘quake over 65,000 and 200,000+ died in the 2004 Asian Tsunami

• It is important to consider why people live, in such large numbers, in areas of great risk

Impacts

• Every hazard event is different, and therefore the specific impacts of disaster vary

• When researching case studies, it is important to be able to identify specific impacts and be able to explain these

• Some impacts are tangible and can be given a financial value. Others are intangible, such as the destruction of a temple or artwork.

• Many losses are direct and immediate such as property damage, but others are indirect – these come later and are harder to quantify, such as stress and psychological damage.

• Impacts are often considered as human (death, injury, illness), economic (property loss, loss of income, cost of relief effort) and physical (changes to landscape and topography).

• Examine the two earthquakes below and consider how factors such as economic development, building types, the geography of the area affected and the relief effort may have affected the impacts

(South Asian) Earthquake October 2005, Kashmir

(Wenchuan) EarthquakeMay 2008, Sichuan, China

Details Magnitude 7.6. Huge number of landslides accounting for 30%+ of deaths

Magnitude 8.0. Thrust fault at continentcontinent convergence

Fault displacement

Largely horizontaldisplacement of up to 10m

Up to 5m vertically and 4m horizontally at the surface

Focus depth 10 km 19 km

Aftershocks 900+ over magnitude 4.0 250+ aftershocks over magnitude 4.0

Deaths 80,000 70,000

People affected 8 million3-4 million homeless

15-30 million 5 million homeless

Injuries 200,000+ 380,000

Damage estimate US$5 billion US$150 billion

Buildings Around 1 million damaged/ destroyed / severely damaged

Over 2 million damaged200,000+ buildings destroyed

Developed versus developing world

• It is often said that disaster impacts in the developed world are largely economic, whereas in the developing world they are human (death).

• You should carefully consider if this generalisation is true. (see the table, right)

• The 1995 Kobe earthquake in Japan and 1991 eruption of Mt Pinatubo in the Philippines are useful examples to consider

Death Toll Event Location Date

5,115 Mount Kelut eruption Indonesia 1991

23,000 Nevado del Ruiz eruption Colombia 1985

25,000Spitak Earthquake Armenia 1988

30,000 Bam earthquake Iran 2003

35,000 Manjil Rudbar earthquake Iran 1990

36,000 Krakatoa eruption tsunami Indonesia 1883

66,000 Ancash earthquake Peru 1970

69,197 Sichuan earthquake China 2008

86,000 Kashmir earthquake Pakistan 2005

100,000 Tsunami Messina, Italy 1908

105,000 Great Kanto earthquake Japan 1923

230,000Indian Ocean tsunami Indian Ocean 2004

245,000 Tangshan earthquake China 1976

Impacts over time

• A simplified version of Park’s hazard response model is shown below

• Different hazard events have different impacts, shown by the speed of the drop in quality of life, the duration of the decline, and the speed and nature of recovery.

• The differences in the 3 lines might be related to type of hazard, degree of preparedness, speed of the relief effort and the nature of recovery and rebuilding.

4. Response to tectonic hazards

• People cope with natural hazards in very different ways

• The chosen ways are often related to wealth and access to technology

• Humans do have a capacity to ignore or seriously underestimate risk, even when it seems obvious to others

• Often it may seem obvious that people should move out of harms way, but in reality this may be impossible.

Hazard modification • Several different approaches can be taken to reduce the impacts of

tectonic hazards:

Modify the event (hazard mitigation)

Modify human vulnerability

Modify the loss

Tsunami Coastal defences and engineering

•Warming and prediction systems•Coastal zone management and landuse planning•Provision of emergency kits

Loss modification involves immediate rescue efforts, followed by relief efforts which focus on food, shelter, water and sanitation.Insurance can help recovery.Long term reconstruction is needed.

Earthquakes Not possible •Ground shaking and liquefaction risk mapping •Aseismic buildings •Earthquake education and drills •Prediction not possible

Volcanoes Lava diversion •Monitoring, prediction warning and evacuation systems •Hazard mapping e.g. lahar risk •Education•Shelters

The hazard management cycle

• Successful hazard management involves a cycle (see diagram) which focuses on the 3 types of modification from the previous slide.

• A focus on modifying loss only, will not improve survival chances when the next hazard strikes

• Long before a natural hazard event, there needs to be a focus on mitigation and prevention (if possible) as well as human preparedness.