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?
Dregg’s 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, 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.
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 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
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