A2 Geography Unit 4 Geographical Research Tectonic Activity and Hazards Important Content. A2...
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Transcript of A2 Geography Unit 4 Geographical Research Tectonic Activity and Hazards Important Content. A2...
A2 GeographyA2 Geography
Unit 4 Geographical ResearchUnit 4 Geographical Research
Tectonic Activity and HazardsTectonic Activity and Hazards
Important Content.Important Content.
What are Natural Hazards and Disasters?
A natural hazard is a natural event with the potential to harm people and their property.
A natural disaster is the realisation and impacts of a natural hazard, I.e. the deaths, injuries, disruption and damage.
What are Natural Hazards and Disasters?
•The EM-DAT international database (www.emdat.be/ ) suggests a hazard becomes a disaster when at least one of the following criteria are met:
– 10+ people are killed.– 100+ people are affected.– A state of emergency is declared.– International assistance is called for.
Dregg’s model of a natural disaster
Classifying natural hazards
•Natural hazards can be classified by physical process.•Hydro-meteorological hazards result from weather systems.•Geophysical hazards result from tectonic processes.•Some hazards are termed context hazards because they have the potential to affect the entire planet. •Global warming is a context hazard.
Hazard trends (3)– Around 50–70 volcanoes erupt
every year.– There is no trend, upward or
downward, in eruption frequency.– Very large magnitude eruptions
(e.g. Mt Pinatubo in 1991) are rare.
– There is a rising trend in the number of people affected (see table). Notice that 8 of the top 10 eruptions have occurred since 1990.
– This reflects growing population density in the developing world.
Country Year
Number of
people
affected
Philippines
(Mt Pinatubo) 1991 1,036,065
Nicaragua 1992 300,075
Ecuador 2006 300,013
Indonesia 1982 300,000
Indonesia 1969 250,000
Comoros 2005 245,000
Philippines 1993 165,009
Papua New Guinea 1994 152,002
Ecuador 2002 128,150
Dem. Rep. Congo 2002 110,400Top ten volcanic eruptions since 1900 by number of
people affected
Global trendsDisasters related to human development levels 1975-2005
Overall, global trends show that the numbers of reported disasters and people affected are rising, but the number of people killed by disasters is falling.
Global trendsImpacts of different disasters 1975-2005
Overall, global trends show drought and famine kill the greatest number of people, earthquakes cause the most injuries and floods stimulate the most homelessness. Thus the nature of the hazard has a significant role to play in determining its human impact.
Volcanoes– Volcanoes occur when magma is forced to the surface
through cracks and fissures in the Earth’s crust.– The degree of volcanic hazard is measured using the
VEI (volcanic explosivity index) scale ranging from 0 to 8.
– Explosivity depends on magma viscosity. The more viscous the magma, the more hazardous the volcano.
– Viscosity depends on temperature, gas and silica content.
– Highly explosive volcanoes erupt low temperature, viscous lava with a high silica content.
– Volcanoes are often places of multiple hazards.
Earthquakes– Earthquakes most commonly occur when two
tectonic plates move suddenly against each other.– Rocks fracture underground at the earthquake focus
and the Earth’s crust shakes as energy is released.– Waves spread from the epicentre, the point on the
surface above the focus.– Earthquakes are measured using the Richter
magnitude scale, and Mercalli intensity scale.– Severe earthquake damage can occur when
unconsolidated sediment undergoes a process called liquefaction. This is often responsible for the worst ground shaking and damage.
Earthquakes
•Cross-section across oceanic/continental plate convergence at a destructive plate boundary
Tsunamis
– Tsunami waves are caused by the rapid displacement of water.
– Submarine earthquakes are the most common cause.– Across the open ocean tsunami waves travel at
speeds up to 700 km h–1. The wavelengths are hundreds of kilometres, but their height is only about 1 m.
– Tsunami waves cannot be seen out at sea. Only as they approach the shore, slow down and increase in height does their potential for destruction become clear.
Human Use systems
Natural systems
Actual NaturalHazard
HazardPerception threshold
PerceptionOf
Hazard
HumanResponse
Modification & Adjustment
Modification & Adjustment
KATES MODEL OF HUMAN PERCEPTION & REPONSE (After Kates, 1992)
Perception & response links.
Perception Response
Acceptance. Do nothing. Accept losses.
Dominance. The technological fix- building dams, forecasting technology,earthquake proofing etc.
Adaptation. •At traditional level lifestyle may be adapted to environmental risks e.g. nomadism.•Modern level means changing human behaviour as well as trying to control environment.