Salt Lake Community College - Geography 1700
Student Name: ___________________
Quiz #3
- Summer, 2014
Score: _____
A. J. Allred, Adjunct
ANSWERS
1. Which of the following travel speeds is faster than the speed of sound (supersonic)?
a. A tsunami wave in deep, open ocean
b. An airplane moving at five miles per minute
c. Earthquake waves moving at only half the speed of an earthquake primary wave
d. Earthquake surface waves moving one tenth of a mile per second
e. Human voices amplified by a loud speaker
The speed of sound varies with air pressure, but is about 750 miles per hour (mph).
a. Open-ocean tsunami waves move at between 400 mph and 500 mph.
b. An airplane moving at five miles per minute is equal to 300 mph, based on 60
minutes in an hour.
c. Earthquake waves moving at ½ the speed of a primary wave are moving at:
Primary wave = 3.7 miles per second
3.7 x ½ = 1.85 miles per second
1.85 miles per second x 60 = 111 miles per minute
111 x 60 = 6,660 mph
d. Surface wave moving at one tenth (1/10) miles per second is equal to:
1/10 x 60 = 6.0 miles per minute
6.0 miles per minute x 60 = 360 mph
e. Surface wave moving at 1/Human voices, whether magnified or not, travel at
the speed of sound (about 750 mph)
2. Prior to FEMA programs, the Mississippi River was known as the “Great Muddy”
because it carried away vast amounts of farm soil. With the use of stream channelization,
the loss of farm soil has mostly stopped, and river obstructions, such as dead tree ‘snags’
and sand bars are a thing of the past.
True ___
False _X__
The first statement was true in the “old days” and it is still true today, regardless of
FEMA programs. In fact, FEMA is mostly about responding to disasters, not preventing
soil erosion. The “Great Muddy” is still washing away vast amounts of earth.
The second statement is not true. Channelization was never applied to most streams and
rivers. That is good! Now that we have discovered problems with channelization were
are learning to avoid doing it.
In fact, channelization does not fully prevent snags, sand bars and other obstructions.
Even fully paved-over streams still require maintenance to prevent plant growth and other
obstructions.
Levee construction often solves some problems but creates new problems, such as
‘bottlenecks’ and a false sense of security. Levees can be undermined, over-topped, bypassed or even washed away. Levee walls tend to constrain normal river flow, making
flood waters higher than in wider channels elsewhere.
3. A tsunami wave originating from a quake 4,000 miles away will probably arrive in about
how many hours?
a.
b.
c.
d.
e.
Slightly more than 12 hours
About eight hours
Four hours
More than ten hours
There is no way to make an accurate estimate without knowing the run-up zone
At a lower-end speed of 400 mph in open ocean, a tsunami wave will travel 4,000 miles
in 8.8 hours. At 500 mph, that distance will be covered in just eight hours.
As the wave shoals (reaches shallow water) it will slow down to about 40 mph, adding a
little bit more time to reach shore.
4. Channelizing a stream can remove obstructions and meander turns, helping move water
more efficiently than natural channels. Channelization is an expensive, but effective river
management method that is growing in popularity in the United States.
True ___
False _X__
Channelization can indeed help waters move more quickly. Channelization is also
expensive, and is no longer growing in popularity. Instead, it is often less expensive and
more effective to let rivers follow “nature’s rules”. People should just keep back at a safe
distance. Rivers should not be expected to handle our shipping cargo, provide recreation,
habitat and other values - - while never misbehaving.
5. With increasing population in Salt Lake County, the amount of hard-surfacing, curbs and
gutters is making many areas more prone to flooding, even though the amount of money
spent on flood control is higher than ever.
True _X__
False ___
As urban areas develop, we do add more flood control structures; however, adding more
people means much more surface paving and roof tops. Overall, adding more people will
tend to out-run our efforts to prevent floods. We just don’t have the resources to deal
with sudden large amounts of water in a basin like Salt Lake Valley, when more than a
million people are present. The size of parking lots and roof tops can shed more water
than some of the very best storm drain systems.
Even the best storm drain systems are not always maintained properly, and many floods
occur when drains are blocked with sand, dead leaves and tree roots.
In Summer 2013, severe local flooding occurred in Taylorsville when poorly maintained
drains prevented rain water from flowing safely away from homes.
There may simply be too many people in Salt Lake Valley.
6. One of the few advantages of high, steep strato-volcanoes is that snow-capped peaks at
least provide significant cooling of volcanic pyroclastics at the most likely exit zone
during eruptions. In addition, the conversion of hot ash to mud tends to reduce block
volcanic flow, reducing the overall hazard to people at lower elevations. The result tends
to be fewer deaths from snowy volcanoes than those located in tropical zones where snow
is not present.
True ___
False _X__
False. The opposite is true: steep, high-elevation strato volcanoes do collect snow caps;
unfortunately, volcanic events can easily melt all of that snow, turning it to fast-moving
streams that are turn to mud “bulldozers” tahat can destroy everything in their paths.
In many cases, the explosive pyroclastics from an eruption (lava, hot gases, ash and
bomblets) are less dangerous than the mud created by hot pyroclastics landing on snow.
7. What is likely the most dangerous combination of factors for volcano hazard?
a. Shallow slopes and heavy vegetation that obscure the source and direction of lava
flows
b. Mafic rocks that are low in silicates and low in dissolved gases
c. Easily visible steep slopes, and rocks that are high in silica and carbon dioxide
d. Massive shield volcanoes such as the Hawaiian Islands that host a world-class ‘hot
spot’
e. None of the above is associated with dangerous volcanoes
On shallow slopes, lava and mud move more slowly, especially if heavy vegetation slows
down the flow.
Mafic rocks are not sticky enough to allow gas pressure to build-up very much. Lack of
gases prevents explosiveness.
Steep slopes are hazardous all by themselves and even worse if they are part of a stratovolcano. Felsic rocks tend to be higher in sticky or viscous rocks (when melted).
Silicon-based rocks tend to be more viscous than other rock types.
When carbon dioxide gases and water vapor (steam) are available in large amounts, then
explosive conditions can be extremely dangerous for anyone nearby. Strato-volcanoes
tend to “blow” more than “flow”.
Massive shield volcanoes tend to be shallow (not steep) and lack enough gas and/or
viscous magma to be explosive. That is one reason why shield volcanoes are not steep;
they are more like simple basaltic lava flows. They “flow” rather than “blow”.
Even though Hawaii and Yellowstone are both “hot spots” – Hawaii is a massive shield
volcano that is not likely to “blow” or erupt explosively.
In contrast, the Yellowstone “hot spot” is not a shield volcano but a caldera, a remnant of
a massive volcanic explosion that collapsed inward and partially filled with water.
8. Utah and the United States both exhibit geologic formations and rock types that are:
a. volcanic in the northeast and sedimentary in the south
b. relatively more volcanic in the west and sedimentary in the east
c. more prone to volcanic eruptions in places where oil, coal and gas are most common
d. very old, and made of sediments that contain large amounts of coal, oil and gas
e. very young, and made of sediments that contain large amounts of coal, oil and gas
For this question, ‘b’ is the best answer ; however, answer ‘d’ is partly true. The eastern
United States and eastern Utah do exhibit large areas of old sediments that often contain
fossil fuels.
9. The cut bank sides of rivers tend to accumulate eroded sediment, thus gradually adding
soil and land area to cut banks over time.
True ___
False _X___
The outside edge of a river (cut bank) gets “cut” and washed away, so the shoreline
recedes, especially during heavy flows. The ‘point bar’ side of the river (the inside of the
turn) receives some of the deposits that were cut away from the cut bank side. So, point
bars and sand bars are collectors of material taken from the cutbank. In fact, the inside
bends of rivers tend to expand over time.
10.Based on class discussion, the longitudinal profile of a river or stream will tend to
become more shallow or flat over very long periods of time.
True _X__ False ___
Streams usually begin in relatively steep country, such as mountains or hills. Surfaces
that are relatively steep tend to erode quickly because steep slopes promote fast, erosive
water flow.
Over long periods of time, mountains and hills wear down and wash away. At the end of
rivers and streams, eroded material is deposited into shallow or flat layers. At oceans and
large lakes, river deltas appear as ‘dump’ grounds for earth materials. Because these
materials are sand, silt and clay, they have little “angle of repose”. Instead, they are
easily flooded and often provide good farm land.
So, the profile of rivers and streams moves from steep to shallow. Were it not for
tectonic forces, all slopes would eventually disappear, as solar energy uses water to erode
everything possible.
11.If unlimited money were available, coastal communities might still be slow to hire
experts to create tsunami “run-up” maps because:
a. Run-up maps are very hard to prepare accurately in places where shorelines are
complex.
b. Property owners will have diverse and strong opinions about how property values
might change when run-up zones are designated.
c. Land development laws might hamper property owners from using their property
freely and maps get out of date.
d. People on vacation, and those who serve them, prefer to avoid distractions that
might discourage anyone from feeling carefree and just playing at the beach .
e. All of the above are true.
Everything above is true. You could have marked all of these on your Scantron card.
12.Inland regions, such as Utah and the Mountain West, may experience seiche or tsunami
waves that are actually more dangerous than ocean tsunami waves because fast-moving
waves of water are confined in small areas where they can pound shorelines heavily,
sometimes going back and forth many times. In contrast, an ocean tsunami wave will
spread its energy over many thousands of square miles.
True _X___ False ____
This question helps test how well you can hold multiple thoughts at once, and evaluate
them as true or false. Often, incorrect information is hidden within statements that are
otherwise true.
In this case, the key is that damage may be worse when energy in water waves is confined
in a relatively small area.
An ocean tsunami may contain vastly more energy than any inland, fresh-water seiche
wave.
However, an ocean tsunami also has long coastlines and the whole ocean for dissipating or
attenuating its energy.
In contrast, confined lakes and reservoirs may experience concentrated wave action as a
seiche wave cannot spread out, diluting its energy.
In fact, a fresh-water seiche wave can refract or reflect back and forth over and over in a
confined area, sometimes ‘scrubbing’ shorelines several times before dissipating.
On rare occasion, an inland seiche wave can be hundreds of feet tall, much taller than
nearly any ocean tsunami, even though the energy in the seiche is much less than an ocean
tsunami.
13.A river delta is almost the same phenomenon as an alluvial fan.
True _X__ False ___
When outwash river flows reach flat terrain, including lakes and oceans, the flow slows
and suspended sediments can settle out. In dry country, a ‘fan’ of river deposits may
collect where mountain streams reach open country.
Where river flow is constant, river deltas are often broken into separate channels because
water flow keeps pushing through sediments that were laid down previously.
14.Portions of a river channel that are slightly more narrow than elsewhere will probably
exhibit:
a. Faster speed of flow
b. Slower speed of flow
c. Higher water level
d. Lower water level
e. Options ‘a’ and ‘c’ are true
The ‘Venturi’ effect causes water or air to pick up speed in order to get the same amount of
fluid through a smaller channel that we might call “bottle neck” or “tight spot”. Water
molecules tend to try to stick together, so speeding up or ‘piling up’ can help keep the
same amount of water flowing even when passing through a “tight spot”.
In fact, water will be domed or taller in the middle of a river or stream channel.
Many river levees tend to “crowd in” on the river, creating a bottle neck. The river tries to
get through by speeding up, which may just help erode the levee.
We should give more room for river flow.
15.For the United States, in areas designated as 100-year floodplain:
a. no new building construction is allowed
b. flood insurance is required
c. the highest floor of new buildings must not exceed the 100-year flood elevation
d. the flood elevation is based upon recorded flood history during many previous 100year periods
e. People should expect a 100-year flood every 100 years.
In many cases, new buildings are allowed in 100-year floodplains if the lowest floor is
above the expected base flood level and if flood insurance is provided.
Answer ‘c’ involves the highest floor, which is not important in flood zones.
Answer ‘d’ is usually not based on flood history, because in most places we have no
recorded history going back more than about 100 years.
Averages are deceiving, because ‘Mother Nature” could deliver two, three or even four
100-year floods in one century, and then no floods at all for long periods of time.
It is best to expect a 100-year flood anytime, especially since we don’t really know for sure
what a 100-year flood might actually do, and because a 500-year flood is also to be
expected.
Mother Nature really doesn’t pay attention to our statistics and estimates. Instead, we
should pay attention to Mother Nature.
16.Compared to foreign countries, in the United States, most dams, canals, pipelines, levees
and other water containment structures are publicly owned and inspected regularly.
True ___
False _X__
Most water control structures are privately owned. Private structures are often not
inspected at all, and in some cases nobody knows who built them or who owns them.
In fact, recent city flooding in Utah caused everyone to wonder “Who is in charge?”
Even with carefully built publicly owned water control structures, money for inspections is
hard to find, and we sometimes don’t know what to look for during inspection. Even if we
find problems, we may not have enough money to fix them.
With Hurricane Katrina we know that many levees and flood walls were not built to last
very long, because in the “old days” we only had enough money to get started on a longterm problem.
After Katrina, we still don’t have enough money to fix everything, so people are once
again living in hazardous areas, hoping for the best.
17.The dry western U.S. states experience relatively few floods compared to wetter regions
in the Eastern United States, and compared to coastal areas that are at risk for tsunami
waves and hurricanes.
True ___
False _X__
Dry country is prone to flash floods, especially because dry country is often steep and
“slick rock”. Steep, hard surfaces help concentrate run-off from brief, heavy rainfall that is
also part of dry climates.
Wet regions tend to have shallower slopes that are covered with vegetation that absorbs
and slows the flow.
Even with construction of dams, reservoirs and other control structures, flooding is still
common in the dry western USA.
18.The dry western U.S. states experiences many landslides and severe erosion because:
a. Landforms are often steep, smooth-sided and hard-surfaced, so water runs off
quickly, causing severe scouring
b. Landforms are often bare, not covered with plants, so mud can flow quickly
downhill
c. Wildfires can remove vegetation that would otherwise hold soil together. Without
that protective cover, hillsides can erode or collapse quickly.
d. Earthquakes are common in the western USA, so steep hillsides can be shaken until
they fall
e. All of the above are true.
19.People who have money like to live on steep slopes because they have a good view of
everything around them. People also like to live above the valley floor because the air is
cooler during summer and the air may be cleaner, with more air pollution collecting at
valley floors. In poor countries, rich people often prefer to live on valley floors so they
can be close to everything in the city. Poor people are compelled to walk up steep slopes
to their homes on hillsides.
True _X__ False ___
People also like to live near water: rivers, streams, oceans.
20.In most cases, people have information that a landslide will occur soon. Most of the
time, people ignore that information. A landslide in Washington State killed more than
50 people a few months ago. That same area experienced landslides in the past. People
did not use that information to protect themselves.
True _X__ False ___
Public safety officials in the area acknowledged that dangerous landslides have occurred in
the same area in past years. People tend to forget, or try to ‘bend’ the rules in order to
build in areas that really should be off-limits.
It is also true that truly safe building sites are becoming more difficult to find. That is also
true in Salt Lake valley.