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 (1)

Hazard trends, 1900–2005

Hazard trends (2)

Number of natural disasters by type, 1970–2005

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.

Volcanoes

• Cross-section of an erupting volcano

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.

Tsunamis

• How a tsunami is generated

Tsunamis

• How a tsunami is generated

Tsunamis

• How a tsunami is generated

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.

Disaster management Cycle

•Disaster management cycle

Falling death tolls suggest improvements in disaster management.