Download Name: number - Atmospheric and Oceanic Sciences

Name:________________________________Student number:____________________
ATOC 250, EPSC 250
Natural Disasters
Mid-Term Examination, 20 October 2008, 6:30-8:30 PM
Instructions: There are 30 questions on this test. Answer your choice of any 25
questions. Each question is worth 4 points. If you answer more than 25 questions, only
the first 25 questions will be marked. All answers should be short-answer, from several
words to several sentences. Provide all answers on the test sheet itself. No aids are
allowed except for translation dictionaries. This test comprises 9 pages.
1) Name at least 4 conditions necessary for the formation of tropical cyclones.
Low values of wind shear
Some form of pre-existing disturbance (front, easterly wave)
Warm water (greater than 270 C)
Warm water to a depth of at least 60m
Sufficiently far from the equator that the Coriolis force can create a circulation
2) Briefly list or discuss the stages (life cycle) of a tropical cyclone.
1) Tropical Depression-First signs of an organized circulation
2) Tropical Storm-System becomes named, some indication of a symmetric structure
3) Hurricane/Typhoon-Eye forms, presence of a banded structure
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3) What makes some areas more susceptible to storm surge damage than others?
A region’s susceptibility to storm surge is largely determined by how steep the
continental shelf is. Regions where there is a shallow slope to the continental shelf will
tend to experience much higher storm surges than regions with a steep continental shelf.
4) Hurricane Katrina is sometimes referred to as a man made disaster. Briefly describe how
human intervention may have contributed to loss of life in the New Orleans area.
A large problem in the New Orleans area is that most of the city is below sea level.
Consequently, levees are built in an attempt to hold back the water, and the levees are
built to a height of about 17 ft above sea level to resist floods and storm surges.
However, if the levees are breached, the flooding that occurs in the city becomes worse
than the flooding that we would have otherwise had because the levees can actually
“trap” the water in the city.
5) What are some of the factors which limit the frequency of hurricane development in the
Atlantic Basin?
Wind shear is too strong
Descending air associated with Azores High
Middle layer of the atmosphere are too dry.
6) The trade winds in the Pacific Ocean are stronger than normal. Are the conditions in
northern Australia likely to be wetter or drier than normal? Explain your answer.
Stronger than normal trade winds will result in warmer water temperatures over
Australia; otherwise known as La Nina conditions. This enhancement of the warm water
results in a stronger Walker circulation, which means that there will be greater rising
motion and more rain than we would normally expect, particularly over northern
Australia.
7) The economic impacts of tropical cyclones are relatively straightforward, but what are
some of the ecological or environmental impacts that these storms can have?
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Two of the most important impacts on the ecology during a hurricane include significant
coastal erosion/destruction from a combination wind and waves, as well as pollution of
streams, lakes, and rivers from inland flood waters, particularly over agricultural areas.
The fertilizer from crop lands can actually run into the rivers and lakes causing algae
blooms, which can in turn kill fish and other organisms.
8) Why is Indonesia so susceptible to negative impacts from El Niño? What are these
impacts?
Indonesia is susceptible to negative impacts from El Nino due to the large bio-mass of
the rainforest. During an El Nino, drought conditions in what is essentially a rainforest
produces conditions that are very favorable for severe forest fires. This can result in
serious health problems for the locals, and can also contribute to greenhouse warming.
9) Perhaps counter-intuitively, drought conditions in normally wet areas can lead to
increases in disease. Briefly explain this apparent contradiction.
In normally wet or lush areas, drought conditions can lead to an increase in stagnant
water as rivers and streams dry out. This can lead to an increase in the mosquito
population, and consequently, to an increase in cases of malaria.
10) What would you expect to happen to typhoon frequency and intensity in the West Pacific
during a strong El Niño event? Briefly explain your answer.
During a strong El Nino, sea surface temperatures over the West Pacific would tend to
be cooler than normal. This would likely result in fewer, and less intense Typhoons in
this region
11) List some of the factors that make present day populations both more and less vulnerable
to natural disasters than 50 years ago.
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Factors that make us more vulnerable mainly center around the fact that there are many
more people who are living in high risk areas such as Miami as compared to 50 Years
ago. Along with that, the potential economic loss from damage to infrastructure is
significantly higher.
Factors that make us less vulnerable are mainly associated with better warning systems,
as well as improved building/infrastructure codes which can mitigate loss.
12) Briefly discuss what some of the factors are that define how a population responds to
warnings of impending natural disasters.
Answers here can be highly varied. One of the many factors that has a large impact is the
idea of collective memory. For example, if people can’t remember the last time a strong
hurricane impacted them, they are less likely to respond quickly to evacuation orders.
Also, the number of false alarms “the boy who cried wolf” syndrome can make people
more complacent in the face of a warning. A person’s financial and physical well being
is also at issue.
13) Explain the difference between “hazard” and “risk”.
Hazard: potential threat to humans and their welfare.
Risk: probability of loss (deaths, injuries, damage, disruption of economic activity) as a
result of a particular natural event.
14) Explain the concept of “recurrence interval”.
Recurrence interval: average time interval between the occurrence of two events of a
given magnitude.
15) Compare and contrast lava flows and pyroclastic flows in terms of their potential hazard.
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Lava generally flows slowly, so there is time to get out of the way, evacuate, etc.
Pyroclastic flows generally move very fast, so little time is available for warning,
evacuation, etc. Thus, pyroclastic flows are significantly more hazardous than lava
flows.
16) Lava domes are viscous extrusions of lava. Explain why lava domes are commonly
associated with explosive activity.
Due to the elevated viscosity of a lava dome, pressure is able to build beneath the dome
to the point where the pressure exceeds the strength of the rock and an explosion occurs.
In a very real sense, lava domes can act as “corks”, with a viscous plug of lava sealing
the top of the conduit, causing the volcano to pressurize.
17) Why was loss of life so high following the 13 November 1985 eruption of Nevado del
Ruiz in Colombia?
A small eruption caused massive melting of the summit glacier. This water mixed with
loose materials such as freshly fallen volcanic ash to generate lahars (volcanic debris
flows) which flowed for tens of kilometers from the volcano. The town of Armero, about
50 km distant from Ruiz, was built on older lahar deposits and was directly in the path of
these newly generated lahars. Although lahar risk at Armero was known to be very high,
people were not evacuated from their homes. These people died when the lahars entered
the town and engulfed them, leading to the loss of ~25,000 people.
18) Why was loss of life relatively small following the cataclysmic 15 June 1991 eruption of
Mount Pinatubo, Philippines?
Scientists decided to evacuate people from areas close to the volcano several days to
weeks before the climactic eruption. Loss of life was thus small.
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19) Kilauea volcano on Hawaii normally erupts basaltic lava flows with little or no explosive
activity. From time to time, however, large explosive eruptions occur at Kilauea. What
mechanism drives these explosions?
When the magma level in the conduit falls to an elevation which is lower than the water
table, groundwater is able to infiltrate into the still-hot conduit. The heating of the
groundwater and its contact with hot rocks and very hot magma lead to explosive
eruptions.
20) In Canada, large ice-clad stratovolcanoes are found in British Columbia along the
Cascadia subduction margin. These volcanoes have the potential to re-activate in the
future and erupt. What is the greatest hazard posed by these volcanoes?
Two answers acceptable here:
(a) lahar generation from melting of summit glaciers
(b) ashfall, which can extend to hundreds of kilometers from the volcano
21) Most earthquakes occur along margins of tectonic plates, but some earthquakes occur in
the interiors of plates. Propose a theory for this observation.
The quakes in plate interiors commonly have a tectonic association with ancient or
inactive rifts or other important fault structures in the crust.
22) Briefly discuss three factors which intensify ground movement due to earthquake
activity.
-high earthquake magnitude
-short distance to epicenter
-shallow depth of quake
-unreinforced buildings; brick, adobe, and mud structures worst
-unconsolidated soils or bedrock such as loose gravels, etc.
-liquefaction
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23) Briefly discuss three hazardous phenomena which can be triggered by an earthquake.
All of the following are acceptable:
-aftershocks
-tsunamis
-landslides
-volcanic eruptions
-fires
-liquefaction
24) Subduction along the Cascadia convergent margin is characterized as “locked” at
shallow levels. What does this locked nature tells us about earthquake hazard and risk in
this area?
Stress is building in the crust which will be released suddenly by a large to very large
earthquake.
25) As subduction occurs along this locked zone, is the upper tectonic plate uplifted or does
it subside?
The upper plate is bent upward by the locked subduction and is thus uplifted.
26) Explain why most meteorites are stony, i.e., they are composed of silicate material.
Most meteorites come from parent asteroid bodies. Asteroids are composed mainly of
silicate rock which constitutes their “mantle”, while their metallic core comprises a
much smaller volume of the body.
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27) Some meteorites are unusual in that they are composed of both silicate material and
metallic material. They commonly have fragmental textures. Propose a theory to explain
these observations.
Two asteroids collided, causing their fragmentation. Metallic core material was
physically mixed with silicate mantle material, which then agglomerated.
Note: other well-argued theories deserve credit.
28) What is the principal difference between a simple impact crater and a complex impact
crater? Discuss this difference.
A complex impact crater exhibits a central uplifted region, caused by rapid
decompression after the initial compression event. The rapid decompression can also
result in very rapid “flash” melting of country rock. These features are not seen in
simple craters.
29) What lines of evidence favor an impact crater origin for the mass extinction which
occurred 65 million years ago?
-the presence of iridium-rich layers at the boundary between the Cretaceous below and
Tertiary above
-the presence of shocked quartz at this boundary
-the presence of crustal melt droplets at this boundary
-the Chicxulub impact crater in the Yucatan, Mexico
30) Both meteorite impact and supervolcano eruptions have been proposed as causes of the
mass extinction 65 million years ago. Discuss the means by which these two phenomena
may have acted in tandem to cause mass extinction.
A large impact would generate wildfires injecting soot into the stratosphere, dust
injected into the stratosphere from pulverized country rock, and sulfur dioxide into the
stratosphere from vaporization of sulfur-rich evaporate rocks. These phenomena would
have caused global winter. Flood basalt eruptions would have emitted significant
amounts of sulfur dioxide into the stratosphere, thereby contributing to the global winter
effect.
On a longer timescale, both an impact event and eruptions may have resulted in
increased atmospheric carbon dioxide, thus global warming, from vaporization of
carbonate rocks in the case of an impact, and from increased acidification of the oceans
in the case of eruptions.
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