6
Billion People and Counting
Joseph Hull and Greg Langkamp
Environmental Outline
# 11:
Hazards and Risk
copyright Joseph Hull and Greg Langkamp
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Natural Hazards
Earthquakes
earthquake = ground shaking
(waves in Earth) caused by fast movement along faults (breaks in Earth's
crust)
more slip along the fault = more groundshaking: slip/movement CAUSES
ground shaking
many active faults near
some edges of continents, on ocean floor, and occasionally within continents
earthquakes +- unpredictable
cause DIRECT damage from
ground shaking and ground breaking
cause INDIRECT damage from
fires, landslides, tsunamis, ground liquefaction, etc.
last monster quake in PNW:
January 1700, magnitude 9. also AD900, downtown Seattle, magnitude
8
earthquakes are nature's
way of getting rid of Earth's internal energy by doing work (moving fault
blocks around)
Tsunamis
very large ocean wave (has
extremely long wavelength but fairly small amplitude or wave height)
caused by fault breaking
ocean floor, or rarely by large submarine landslide
tsunamis travel very fast
across ocean (100's of kms per hour) and can travel across entire Pacific
Ocean
takes about 12-14 hours for tsunami to travel from Japan to Washington
State (and vice versa)
waves become very tall and
destructive when they enter shallow water, can be 20-30 meters high in
extreme cases
lots of potential damage
along Pacific Rim; Washington's southwest coast at high risk (but few residents)
tsunami in Puget Sound associated
with AD900 quake, also caused seiche wave (soup bowl wave) in Lake Washington
quakes and slides +- unpredictable,
therefore tsunamis unpredictable, but warning systems can help unless quake
is close.
Mass Movements (Landslides, Mudflows, etc.)
movement of earth materials
(soil, loose rock, vegetation, sand and gravel, mud and clay) downhill
and downslope
if slides as block = SLIDE
(landslide, e.g.), if flows like water = FLOW (mudflow, e.g.)
contributing factors:
steep slopes, weak earth materials, heavy rainfall and/or lots of groundwater,
human disturbance
sort of predictable some
places: in Seattle, 4 days of rainfall averaging 1 inch per day during
wet season = MASS MOVEMENTS
can cause lots of property
damage and sometimes death and injury but not on a great scale
mass movements are nature's way
of flattening out slopes without using bulldozers and dynamite
Volcanic Eruptions
volcanoes: cone-shaped
pile of lava flows and airfall debris, built up in layers over time
"quiet" volcanoes like Hawai'i
made up of well-behaved lava flows and very little airfall ash/tephra.
can damage farms, homes, roads etc. (buried by lava) but not life-threatening,
plenty of time to get out of way
"explosive" volcanoes like
Mt. St. Helens, Pinatubo, Etna made of both flows and ash
ash and volcanic mass movements can travel far from volcano and cause injury
and death
volcanic mass movements:
several different flavors, depending upon type of volcano
huge landslides on volcano can trigger eruptions. e.g. Mt. St. Helens
1980
eruptions/landslides can turn soupy as they move downhill, turn into lahars
and travel long distances
e.g. 300 year old lahars along Duwamish River near West Seattle bridge
from Mt. Rainier!!
volcanic eruptions are nature's
way of getting rid of internal heat of Earth.
Wildfires (in part)
Human-Induced Hazards
Wildfires (in part)
Petroleum Spills
Automobile Accidents
Radioactive Releases from Nuclear Power Plants
______________________: insert your favorite
here
Power Law Frequency Distribution
many hazards show a special pattern of sizes:
many small ones, some medium ones, a few big ones
example: earthquakes
in WA. Magnitude 3 = once per year, Mag 6 = once per 30 years,
Mag 7 = once per 100 years
make a plot of X = size versus Y = frequency of
hazard of that size, see "L-shaped" curve of decreasing frequency with
size
power law or power function often fits this L-shaped
curve the best. power law has form Y = a X ^b
b is negative in this case,
because frequency decreases with increasing size
example: earthquakes
in Missouri, frequency = 1927 magnitude ^(-.876)
Fractals and PLFD
many objects show a special pattern of sizes:
many small ones, some medium ones, a few big ones
e.g. arteries in the human
body. streets in a city. streams in a drainage basin.
branches on a tree. frondlets on a fern. etc.
these objects all have a special space-filling property:
no matter how closely you look, there are ever smaller fronds, branches,
etc.
the pattern of fronds, branches, etc. looks
the same no matter what scale you are looking at. called self-similar
objects with this space filling self-similarity
are called fractal. (fractal is just a made up word for "fractional
dimension")
fractal objects have power law frequency distributions;
many small ones, some medium ones, a few big ones !!!!
therefore earthquakes, landslides, petroleum spills,
automobile accidents, etc. are all fractal
fractal in a different sense
than fern fronds or arteries; not filling up "space" like branches do.
with objects that show a normal or bell-shaped distribution
of sizes, there is a characteristic size (in the middle, near the
mean)
e.g. measure the height
of corn stalks, typical or characteristic height is about 3 meters, some
taller, some shorter
with objects that show a fractal or power law distribution
of sizes, there is NO characteristic size
the closer you look, the
smaller the size; the farther back you stand, the bigger the size.
What is the biggest oil spill possible?? only
limited by the size of the oil tanker......
What is the "typical" oil spill size?? There
is no such thing....
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