ENVS4012 chapter 1

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Published on 19 Apr 2013
School
University of Guelph
Department
Environmental Sciences
Course
ENVS 4012
Professor
Chapter 1 – Introduction to Natural Hazards
-process: meaning the ways in which events, such as volcanic
eruptions, earthquakes, landslides, and floods, affect Earth’s surface
- the processes we consider to be hazards are natural and derive from
the internal heating of Earth and external energy from the Sun
- the amount of energy released by natural processes differs greatly (ex.
average tornado expends about 1000x as much energy as a lightning
bolt does, whereas the volcanic eruption of Mount St. Helens released
approx 1 million x as much energy as a lightning bolt
- the earth receives approx 1 trillion x as much solar energy than a
lightning bolt. Note: a lightning bolt focuses its energy at a point
whereas solar energy is spread around the entire globe
- events such as earthquakes, tsunami, floods and fires are natural
processes that have been occurring on earth’s surface for billions of
years
- not all hazards are “natural”. Many hazards are caused by people
(pandemics, warfare, etc.)
Hazard, Risk, Disaster, and Catastrophe
-hazard: any natural process that threatens human life or property.
The process itself is not a hazard; rather it becomes a hazard only
when threatening human interests
-risk: the probable severity that a destructive event will occur
multiplied by the event’s likely impact on people and property.
Integrates hazard and social vulnerability
-disaster/catastrophe: events that cause serious injury, ,loss of life,
and property damage over a limited time and within a specific
geographic area
- catastrophes are more massive than disasters and affect a larger
number of people and more infrastructure
- disasters may be regional or even national in scope, whereas
catastrophes commonly have consequences far beyond the area that
is directly affected and require huge expenditures of time and money
for recovery
- The OFDA/CRED International Disaster Database & The Centre for
Research on Epidemiology of Disasters defines a disaster must be
responsible for a minimum of 30 deaths
- no area is considered hazard free
- during the past few decades:
oannual loss of life = 150 000
odeaths in 2005 alone = 300 000
ofinancial loss = $50 billion per year
ofinancial loss in 2005 alone = $200 billion
- the UN designated the 1990s as the International Decade for Natural
Hazards Reduction. The objectives were to minimize loss of life and
property damage from natural disasters, but these objectives were not
met, rather losses from disasters increased dramatically in the 1990s
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oAchieving the UN objectives will require education and large
expenditures to mitigate specific hazards and contain diseases
that accompany disasters and catastrophes
-mitigation: used by scientists, planners, and policy makers when
describing efforts to prepare for disasters and to minimize their
harmful effects. Ex. after floors, water supplies may be contaminated
by bacteria, causing disease to spread. To mitigate the effects of this
contamination, a relief agency or govt may arrange for portable water
treatment plants, disinfect water well, and distribute bottled water
Death and Damage Caused by Natural Hazards
- in north America, tornadoes and windstorms cause the largest number
of deaths each year
- loss of life from earthquakes in north America is surprisingly low,
largely because of their high standards of building construction
however they can cause tremendous property damage
- the relation between loss of life and property damage noted above
only applies to north America and the fully developed world
- natural disasters in most developing countries claim far more lives
than comparable events in north America
- overall, damage from most hazardous natural processes in Canada is
increasing, but the number of deaths from many hazards is decreasing
because of better planning, forecasting, warning, and engineering
Role of Time in Understanding Hazards
- natural disasters are recurrent events; therefore, study of their history
provides needed information for risk reduction
- knowledge of historic events and the recent geologic history of an area
is vital to understanding the hazard and assessing its risk
- Geologists have the tools and training to “read the landscape” for
evidence of past events, and by linking prehistoric and historic records,
they extend our perspective of recurrent natural events far back in
time
- hazard forecasts and warnings are more accurate if we combine
information about the past behaviour of the process with an
understanding of present conditions
Geologic Cycle
-geologic cycle: the four associated sequences of Earth processes:
othe tectonic cycle
othe rock cycle
othe hydrologic cycle
obiogeochemical cycles
The Tectonic Cycle
- tectonic cycle involves the creating, movement, and destruction of
tectonic plates, and one cycle can last more than 200 million years
- the term tectonic refers to the large-scale geologic processes that
deform Earth’s crust and produce features such as ocean basins,
continents and mountains
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- Tectonic processes are driven by forces deep within earth
- Tectonic plates: large blocks that form the outer shell of earth; 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 subjection zones
Earth’s Lithosphere and Crust
- earth comprises several internal layers that differ in composition and
physical properties
- Outermost or surface layer: lithosphere stronger and more rigid
than deeper material. Average thickness is about 100km, ranges from
a few km thick beneath the crests of mid-ocean ridges to 400k, thick
beneath continents
- Below the lithosphere: asthenosphere hot layer of relatively low-
strength rock that extends to an average depth of about 250km
- upper part of the lithosphere: crust crustal rocks are less dense
than the rocks below.
- There are two types of crust: oceanic crust and continental crust.
Oceanic crust is denser than continental crust. It is also thinner – the
ocean floor as an average crustal thickness of about 7km, whereas
continental crust is about 30km thick and up to 70 km thick beneath
mountainous regions
Types of Plate Boundaries
- unlike the asthenosphere which is thought to be more or less
continuous, the lithosphere is broken into large fragments called
lithospheric or tectonic plates that move relative to one another
- Processes associated with the origin, movement, destruction of these
places are termed plate tectonics. Tectonic plates are formed and
destroyed at their margins or boundaries
- plate boundaries may be divergent, convergent, or transform
- these boundaries are rather broad zones of intense deformation 10s to
100s of km wide that extend through the crust
- It is at these boundaries that most earthquakes and active volcanoes
occur
-Divergent boundaries occur where two plates move away from each
other and new lithosphere is produced. Places where this separation
occurs are large, underwater mountain ridges known as mid-ocean
ridges. By a process known as seafloor spreading, lithosphere breaks
or rifts apart along a series of cracks more or less parallel to the ridge
crest. Many of the cracks in the underwater rift zone are injected with
molten rock, or magma from below. New lithosphere forms as the
magma solidifies and is slowly rafted, in a conveyor-belt fashion away
from the ridge crust. The tectonic plates on each side of the ridge
move apart at 10s of mm to a few 100 mm each year
-Convergent boundaries occur where two plates collide head on.
Commonly, a higher density oceanic plate is drawn down beneath a
lower density continental plate process called subduction and
convergent boundaries of this type are called subduction zones. The
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Document Summary

Many hazards are caused by people (pandemics, warfare, etc. ) Disaster/catastrophe: events that cause serious injury, ,loss of life, Hazard: any natural process that threatens human life or property. The process itself is not a hazard; rather it becomes a hazard only when threatening human interests risk: the probable severity that a destructive event will occur multiplied by the event"s likely impact on people and property. The ofda/cred international disaster database & the centre for. Mitigation: used by scientists, planners, and policy makers when describing efforts to prepare for disasters and to minimize their harmful effects. Ex. after floors, water supplies may be contaminated by bacteria, causing disease to spread. To mitigate the effects of this contamination, a relief agency or govt may arrange for portable water treatment plants, disinfect water well, and distribute bottled water. Geologic cycle: the four associated sequences of earth processes: the tectonic cycle, the rock cycle, the hydrologic cycle, biogeochemical cycles.

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