A2 Geography Unit 4 Geographical Research Tectonic Activity and Hazards Important Content. A2 Geography Unit 4 Geographical Research Tectonic Activity and Hazards 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 ( ) 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 – This reflects growing population density in the developing world. CountryYear Number of people affected Philippines (Mt Pinatubo)19911,036,065 Nicaragua ,075 Ecuador ,013 Indonesia ,000 Indonesia ,000 Comoros ,000 Philippines ,009 Papua New Guinea ,002 Ecuador ,150 Dem. Rep. Congo ,400 Top ten volcanic eruptions since 1900 by number of people affected

Global trends Disasters related to human development levels 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 trends Impacts of different disasters 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 Natural Hazard Perception threshold Perception Of Hazard Human Response Modification & Adjustment KATES MODEL OF HUMAN PERCEPTION & REPONSE (After Kates, 1992)

Perception & response links. PerceptionResponse 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.