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?
Dreggs model of a natural disaster 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. 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, 19002005 Hazard trends (2) Number of natural disasters by type, 19702005
Hazard trends (3) Around 5070 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. Top ten volcanic eruptions since 1900 by number of people affected 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 110,400 Global trends Disasters 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 trends Impacts 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 Earths 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 Earths 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 h1. 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
KATES MODEL OF HUMAN PERCEPTION & REPONSE (After Kates, 1992) Modification & Adjustment Human Use systems Actual Natural Hazard Hazard Perception threshold
Perception Of Hazard Natural systems Modification & Adjustment Human Response 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 Falling death tolls suggest improvements in disaster management. Disaster management cycle
