1. 6GEO4 Unit 4 Tectonic Activity and Hazards

2. 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
Landslides
Liquefaction
Volcanoes
Lahars

3. Tectonic activity and causes Tectonic hazards physical impacts
CONTENTS
Tectonic activity and causes
Tectonic hazards physical impacts
Tectonic hazards human impacts
Response to tectonic hazards
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4. 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

5. 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.

6. 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

7. 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.

8. 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.

9. Magma generation
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
Magma
type
Generation
Tectonic setting
Hazards
Basaltic
Low 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
Rhyolitic
High 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

10. 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

11. 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.

12. 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

13. 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)

14. 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.

15. 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

16. 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

17. Earthquakes and faults
Tectonic movements and movements along faults (which generate earthquakes) also produce distinctive landforms and relief:
Note: diagram not to scale

18. 3. Tectonic hazards human impacts
Living in areas of tectonic risk?
Ignorance of the risks and / or underestimation of risk
Inertia; always lived there
Nowhere else to go / lack of alternatives
Choice e.g. fertile farmland or tourism
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

19. 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).

20. (South Asian) Earthquake (Wenchuan) Earthquake
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) Earthquake
May 2008, Sichuan, China
Details
Magnitude 7.6. Huge number of landslides accounting for 30%+ of deaths
Magnitude 8.0. Thrust fault at continent
continent convergence
Fault displacement
Largely horizontal
displacement 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 million
3-4 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 damaged
200,000+ buildings destroyed

21. Developed versus developing world
Death Toll 
Event 
Location 
Date
5,115
Mount Kelut eruption
Indonesia
1991
23,000
Nevado del Ruiz eruption
Colombia
1985
25,000
Spitak Earthquake
Armenia
1988
30,000
Bam earthquake
Iran
2003
35,000
Manjil Rudbar earthquake
1990
36,000
Krakatoa eruption tsunami
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
230,000
Indian Ocean tsunami
Indian Ocean
2004
245,000
Tangshan earthquake
1976
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

22. 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.

23. 4. Response to tectonic hazards
Do nothing (ignore the risk)
Move to a safer location
Attempt to prevent the hazard
Adapt lifestyle to the hazard
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.

24. 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

25. 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.