6GEO4 Unit 4 Tectonic Activity and Hazards

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.

3. CONTENTS • Tectonic activity and causes • Tectonic hazards physical impacts • Tectonic hazards human impacts • Response to tectonic hazards Click on the information icon to jump to that section. Click on the home button to return to this contents page

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

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 • 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. 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

21. 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

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 • 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:

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.