Download doc makeup midterm 2012 w/answers

Name:________________________________Student number:____________________
ATOC 185 / EPSC 185
Natural Disasters
Make-up Mid-Term Examination, 16 October 2012, 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. Good luck.
1. Where do the largest earthquakes occur, along divergent, convergent, or transform
plate boundaries? Explain your answer.
The largest earthquakes occur along convergent margins due to the large amounts of
friction and stress produced by the subducting or colliding plates.
2. Cascadia in the Pacific Northwest is an area where subduction is occurring, yet
the level of seismicity is low compared to other subduction zones worldwide.
Discuss the significance of this observation.
The level of seismicity is low because the two plates are locked at a certain depth, hence
faulting and earthquakes are less common than at other subduction zones. At the same
time, the locked nature of the plates is causing large amounts of stress to build within the
subduction system, increasing the probability of a future large earthquake.
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Name:________________________________Student number:____________________
3. Why do so many thrust faults occur in the Los Angeles area?
East of Los Angeles, the San Andreas Fault is not straight, taking a bend. As a result, the
strike-slip fault movement is not smooth and efficient. Instead, part of the Pacific Plate on
which LA sits pushes against the North American Plate, causing compression and thrust
faulting to occur in the LA basin.
4. Compare earthquake vulnerability in San Francisco today compared to 100 years
ago.
Modern building codes were not in place 100 years ago. Hence buildings and urban
environments were highly vulnerable to earthquakes such as the 1906 event. On the other
hand, the San Francisco area has grown substantially since 100 years ago, so many more
people are at risk today. Our level of preparedness and understanding is better today
than it was 100 years ago, but our ability to predict earthquakes remains poor.
5. Where is seismic hazard greatest in Canada, and why?
Seismic hazard is greatest along the western coast of BC and the Yukon, since this region
is subjected to subduction and active strike-slip faulting.
6. This week many people in Montreal felt a magnitude 4.5 earthquake. Why do
such earthquakes occur in the Montreal region, despite the fact that Montreal is
located in the interior of the North American tectonic plate?
During the breakup of the supercontinent of Pangea starting about 200 million years
ago, new rifts began to form or were re-activated in various parts of the supercontinent.
One of these rift structures follows the St Lawrence valley. Faults from this rifting event
are still active today, as witnessed by the occurrence of these earthquakes.
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Name:________________________________Student number:____________________
7. Earthquakes can trigger other naturally-occurring hazardous phenomena. Discuss
two examples.
Fires, landslides, aftershocks, tsunamis, liquefaction
8. On a global scale, discuss seismic and volcanic hazards in terms of plate
tectonics.
Both seismic and volcanic activity is most intense and most frequent (by far) along plate
tectonic margins.
9. Earthquakes and eruptions both occur along mid-ocean ridges. Explain (a) the
types of faults which generate these earthquakes and (b) the composition of lava
produced by the eruptions.
(a) Normal faults are produced by tension as the two oceanic plates move apart.
(b) The lava is basaltic in composition (~50% SiO2).
10. Both cinder cones and shield volcanoes erupt mainly basaltic lava, yet their forms
and sizes are very different. Discuss these differences.
Cinder cones erupt only once in their lifetime, hence are very small structures. The
eruptions can be both violent and calm; as a result, both pyroclastics building a cone and
lava flowing out further occur. Shield volcanoes are long-lived volcanic structures
emitting mainly basaltic lava. Since the eruptions are frequent with long, fluid lava flows,
the volcano builds itself with gentle slopes over time.
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Name:________________________________Student number:____________________
11. Does basaltic lava flow faster or slower than rhyolitic lava? Explain your answer.
Basaltic lava flows faster than rhyolitic lava due to its lower silica content and higher
temperature.
12. Are shield volcanoes or stratovolcanoes more prone to sector collapse? Justify
your response.
Compared to shield volcanoes, stratovolcanoes are generally steeper due to highviscosity andesitic lava flows and low-strength pyroclastic materials. As a result,
stratovolcanoes are more prone to failure.
13. Discuss two similarities between the 18 May 1980 eruption of Mt. St. Helens in
Washington State and the June 1991 eruption of Mount Pinatubo in the
Philippines.
-both are andesitic subduction-related stratovolcanoes
-rapid increase in activity and short warning times before the cataclysmic eruptions
-during the climactic eruption, pyroclastic falls, pyroclastic flows, and lahars were
generated
-loss of life was relatively small in both cases
14. Where is volcanic hazard in Canada greatest, and why?
Volcanic hazard is greatest along the Cascadia subduction zone of British Columbia,
both from stratovolcanoes in BC as well as distant effects (e.g., ashfalls) from Cascade
stratovolcanoes across the border in the USA.
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Name:________________________________Student number:____________________
15. How does a caldera form?
If a substantial volume of magma is drained and erupted from a magma reservoir, the
roof of the reservoir is no longer supported, hence collapses partway into the magma
chamber, creating a surface depression called a caldera in the process.
16. The subduction-related Cascade volcanoes of the Pacific Northwest in the USA
and Canada are commonly draped in snow and ice. Why are some communities
located far from these volcanoes still at risk from an eruption of one of these
volcanoes?
These volcanoes have the ability to generate lahars which are highly mobile and can flow
far from source.
Since these are generally explosive volcanoes, they can also produce abundant ash which
can impact distant communities.
17. What is the main volcanic hazard to aircraft? Give one example (case study) of
this type of hazard.
The main hazard is volcanic ash suspended in the atmosphere which can damage or
destroy jet engines. Examples of aircraft-volcanic ash encounters include Galunggung
1982, Redoubt (Alaska) 1989, Pinatubo (Philippines) 1991, and Eyjafjallajökull (Iceland)
2010.
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18. List the three potential triggers for tropical cyclones. What do all three of these
things have in common?
Three potential triggers for tropical cyclones are 1) The intertropical convergence
zone, 2) easterly waves, and 3) cold fronts. The one thing that all of these features
have in common is that they are regions of convergence that can produce
thunderstorms.
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Name:________________________________Student number:____________________
19. Discuss how you would be able to distinguish a Tropical Storm from a Hurricane
using only satellite pictures.
The most distinguishing characteristic between a tropical cyclone and a hurricane in
a satellite picture is the presence of clear eye feature in the center of the hurricane
that you would not find in a tropical storm.
20. Explain why a nearly stationary tropical cyclone is less likely to be an intense
cyclone than one moving at 20 kilometers per hour.
The main source of energy for a tropical cyclone is warm water which generally
exists in a thin layer near the surface of the ocean. A stationary cyclone would cause
enough mixing in the ocean that cooler water would upwell under the storm causing
the storm to weaken.
21. You are the mayor of a city located on the coast of Texas. Discuss two things that
you would do minimize loss of life and property damage in the event that a
hurricane strikes your city.
There are too many possible answers to discuss them all, but two of the most
plausible responses are 1) build a sea wall or levees to protect the city from storm
surge and 2) create an evacuation plan for the city. Several people mentioned that
they would “raise the city” which would help, but is generally implausible to do.
22. Discuss three factors that make Bangladesh particularly susceptible to loss of life
from a tropical cyclone.
Factors that contribute to the high death rates from tropical cyclones include, but are
not limited to 1) close proximity to a warm body of water, 2) very low elevation above
sea-level (they are NOT below sea level), 3) very high population density, and 4)
poverty with relatively poor infrastructure.
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Name:________________________________Student number:____________________
23. Explain why tropical cyclones never develop near the equator.
Tropical cyclones never occur near the equator because there is not enough Coriolis
Force or deflection to allow rotation to develop. Consequently, air simply blows from
high to low pressure near the equator and storms never develop.
24. There is a category 3 hurricane in the Atlantic Ocean moving east towards Miami,
Florida. If you are an emergency management official, would you be more likely
to evacuate the northern or southern side of the city? Be sure to justify your
answer.
Ok, I screwed this question up a bit in that the storm should have been moving westward
and not eastward. Consequently, either side of the city was an acceptable answer as long
as the reasoning was because the motion of the storm would add to the strength of the
winds on one side of the storm and would subtract from the wind speed on the other side
of the storm.
25. A few days before a devastating hurricane hit Galveston, Texas, back in 1900, the
meteorologist in the city was warned that there was a cyclone in the Gulf of
Mexico. In spite of this, he remained confident that Galveston would not be
impacted by the storm. Explain why this was the case.
Conventional wisdom at the time was that all tropical cyclones recurved into the Gulf
Coast States or simply died before reaching Texas. This was because up until 1900, a
strong tropical cyclone had not impacting the relatively young settlements in Texas.
26. Discuss the one most important advancement in technology that has greatly
increased our ability to track tropical cyclones.
The single most important advancement in the ability to track cyclones was the
implementation of weather satellites. This allowed us to observe cyclones wherever
they are around the globe without having to rely on direct observations.
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Name:________________________________Student number:____________________
27. Briefly discuss how warm water serves as the energy source for tropical cyclones.
The key here is the concept of latent heat release. Warmer water produces more
water vapour in the atmosphere through evaporation. This water vapor then can get
condensed, releasing heat into the atmosphere. This release of heat is essentially the
energy source of the tropical cyclone.
28. Scientists often say that natural disasters are non-deterministic. Explain what is
meant by that statement.
The statement refers to the fact that most systems in nature are chaotic in that they
are very sensitive to the initial conditions. This makes them difficult if not impossible
to precisely predict with 100% confidence. Consequently, we often refer to the
probability of an event occurring as opposed to simply saying something will or will
not happen.
29. Explain what is meant by a 100 year flood.
A hundred year flood is a flood that statistics show is likely to occur approximately
once every 100 years or so.
30. Give two reasons as to why the city of New Orleans is perhaps the most
VULNERABLE city in North America in terms of loss from a hurricane.
By far the most important aspect that contributes to the vulnerability in New Orleans
is the fact that the city is below sea-level. This means that levees have to be built to
keep the ocean out, but when they fail, they can actually cause flood levels to be
higher than they would be otherwise. Also, the poverty of the city means that many
people don’t have the means to evacuate the city on their own.
*** Not for student use. For use in grading exam paper only. ***
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