GG231 Study Guide - Midterm Guide: Mudflow, Pyroclastic Flow, Volcanic Glass
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GG231 Midterm Review
Lesson 1 – Introduction
Risk – the product of the probability of a hazardous event and the expected damage if the event
Hazard – (Natural) A natural process that poses potential threat to people and property
Disaster – A brief event that causes great damage or loss of life in a limited geographic area.
Response Sequence to a Disaster (Recovery)
The first two weeks after a disaster are the period of emergency, during which normal
activities cease or are changed. In the restoration phase which typically lasts several
months, normal activities return, although perhaps not at pre-disaster levels. Finally during
reconstruction the capital stock is replaced, major new construction is completed and
normal activities return. *Fig 1.16 page 24
Types of Disasters
• Natural Hazards
• Technological Hazards
• Violence and war hazards
release of dangerous natural forces
release of dangerous technological forces
armed forces and weapon systems
strategies and tactics
Vulnerability to Hazards
Much of human vulnerability has little or no relationship to the particular hazard, such as
tornadoes or chemical release. It is related to activities and circumstances of everyday life.
Vulnerability is more likely to be dependent on age, gender and health status, and how
society treats its members or different groups. Vulnerability also depends upon the quality
and siting of buildings and land uses; public infrastructure and services; and ways of life
and political authority.
Above all vulnerability involves the general and active capacities of people, what enables
them to avoid, resist and recover from harm. While, a hazards perspective tends to explain
risk and disaster in terms of external agents and their impacts, vulnerability looks to the
internal state of a society and what governs that. Vulnerability in the modern world
depends upon the legal, political and moral frameworks of civil society. In more traditional
societies, it depends upon customary obligations and communal support structures
Hewitt identifies six forms of vulnerability:
• exposure to dangerous agents and environments
• weaknesses predisposition of persons, buildings, communities or activities to greater harm
• lack of protection against dangerous agents and for weaker persons and items
• disadvantage lack of the resources and attributes to affect risks or respond to danger
• lack of resilience limited or no capability to avoid, withstand or offset and recover from disaster
• powerlessness inability to influence safety conditions, or acquire means of protection and relief
Intervening conditions are those not directly related to a given hazard or human
vulnerability to particular stresses. It includes circumstances that intervene between the
two. For instance, as you will learn in Module One, the impact of an earthquake on a city can
be influenced by particular soil type, topography, vegetation cover and water tables.
However, these conditions are not dependent on the tectonic activity nor the built
structures. They have their own, distinct geographic patterns. They intervene between
seismic events and vulnerable structures and to a different extent from place to place
Similarly, institutional and cultural phenomena may buffer or focus damage without being
tied to specific vulnerabilities or agents of damage. The form and development of
settlements, occupations and who is obliged to live where, also happen to be critical for
storm or flood risks. International grain prices and local grain stocks can influence whether
famine will be allowed to develop in a particular country. Food distribution policies and
market prices can decide who and how many people, will starve, even where sufficient food
is actually available (Hewitt, 1999).
Risk considers the exposure to dangers, adverse or undesirable prospects and the
conditions that contribute to danger. Risk analysis considers potential and assessed
dangers. Typically one considers past damages to define levels of danger attached to groups,
activities and everyday life. By understanding or predicting the risk we can possibly reduce
or eliminate the possibility of a disaster. This is not a course on risk assessment, such as
smoking and life expectancy, car insurance, etc. This form of risk has a long history in
favourable and adverse future results, profits and losses, game theory, winning and losing
and has been covered extensively in texts on insurance. The main focus in this course is the
question of public safety and social security, focusing on the adverse outcomes and
possibilities for prevention and mitigation.
Most deadly disasters
Natural - http://www.disastercenter.com/disaster/TOP100K.html
Technical - http://www.disastercenter.com/disaster/TOP100P.html
Lesson 2 – Earthquakes, Tsunamis
Main Causes of Earthquakes
The earthquake hazard is a function of a number of factors. The physical processes are
linked to factors such as where did the quake originate or at what depth below the earth's
surface, the structure of the bedrock, etc.
where rupture on fault plane started – seismic energy leaves this point (a.k.a. the
point on surface above the focus
Earthquakes are frequently triggered along a fault line you are probably familiar with the
San Andreas Fault in California. The tsunami that struck Indonesia in 2004 also originated
from an earthquake that started along a fault.
A fault along which the hanging wall has moved down relative to the footwall.
A fault along which the hanging wall has moved upward relative to the footwall
Low angle reverse fault along which older rocks are displaced over younger rocks.
A very large, fault bounded block of crust and upper mantle that slowly moves on top of the
asthenosphere. Tectonic plates form at mid oceanic ridges and are destroyed at subduction
An elongate zone, typically hundreds to over a thousand km long, where two crustal plates
converge, one moving slowly under the other. (Largest earthquakes are subduction ones)
Another scale is used to measure the impact or damage from the earthquake the Modified
Mercalli Scale. This scale focuses more on the impact to society such as the number of
deaths, buildings collapsed, etc.
The primary damage comes from injuries and death caused by failed buildings. It is direct
damage that is physical or mechanical. It can be minimal, with only cracked plaster, or as
extensive as failure of the structure. The shaking weakens the bearing strength of the