5.Which soil is probably a dense, heavy clay?These questions should give you an idea of the kind of thinking I am after, and the way the questions may be structured. Answers to the questions, along with the reasoning, are given at the bottom of this page. I suggest that you try to take this exam without looking at the answers -- then check and see how you've done. When you miss a question, use my explanations to help figure out where you went wrong.
1. Which rock should produce the least clay on thorough chemical weathering in a cool temperate climate?
a. granite b. quartz sandstone c. greenstone d. feldspar-rich gabbro e. they would all produce about the same amount
2. A soil formed by thorough chemical weathering of gabbro (mineral content: pyroxene, plagioclase) in the tropics would consist mostly of
a. silica b. quartz and clay c. pyroxene and clay d. iron oxides and alumina e. olivine and pyroxene grains
3. If the same gabbro were weathered in a very arid area, the upper part of the soil would probably consist mostly of
a. plagioclase and pyroxene grains, along with a little clay and iron oxide b. calcium carbonate and alumina c. quartz and clay d. nearly pure silica e. humus
4. In a humid temperate forested area, which of the rocks below would probably weather the fastest?
a. silica-cemented quartz sandstone b. granite c. basalt d. limestone e. clay
Questions 5-8 refer to the diagram below
a. 1 b. 2 c. 3 d. 4 e. there is no way to tell
6. Which soil is probably a gravel or coarse sand?
a. 1 b. 2 c. 3 d. 4 e. there is no way to tell
7. One of these soils is in a heavy forest. Which one is the most likely candidate?
a. 1 b. 2 c. 3 d. 4 e. there is no way to tell
8. One of these soils is rich in swelling clay (montmorillonite). When dry, this soil shrinks greatly and many cracks open up. As it gets wet, the clays swell and the cracks close. Which graph represents this soil?
a. 1 b. 2 c. 3 d. 4 e. there is no way to tell
9. Which soil would be best if you were looking for a site for a septic tank drain field?
a. 1 b. 2 c. 3 d. 4 e. all would be equally good
10. On which soil would overland flow be most readily generated?
a. 1 b. 2 c. 3 d. 4 e. all would generate equally readily
11. In a barren rocky drainage basin, most of the water appearing as streamflow during storms gets to the stream by:
a. direct overland flow (Horton overland flow) contributed from nearly the whole basin area
b. overland flow from saturated areas close to the stream channel (saturation overland flow)
c. water moving downslope to the stream through the unsaturated zone of the soil (subsurface stormflow)
d. increased groundwater discharge into the stream
e. rain falling directly into the stream
12. The average annual rainfall over a forested drainage basin is 70 inches. Evapotranspiration by
plants averages 35 inches per year. About 10 inches of water per year percolates down to the
water table and becomes groundwater. What is the average annual surface runoff (streamflow) for
this drainage basin?
a. 10 inches b. 25 inches c. 40 inches d. 60 inches e. 70 inches
13. As a heavily cut-over (logged) area becomes reforested, what do you expect would happen to the
average discharge of streams draining the area?
a. it would probably increase, chiefly because more water would infiltrate b. it would probably increase, chiefly because less water would evaporate from the soil c. it would probably decrease, chiefly because there would be less overland flow d. it would probably decrease, chiefly because more water would be lost by evapotranspiration e. there would probably be no change in streamflow
14. Which one of the items below decreases the potential for soil erosion on a hillside?
a. removal of plant cover
b. steep slopes
c. high infiltration rate
d. high water table
e. downslope concentration of water
15. Bankfull discharge is
a. the discharge at which the stream just starts to leave its banks and flow onto the floodplain
b. is equalled or exceeded in about two out of three years on the average
c. is the discharge primarily responsible for forming and maintaining the stream channel
d. all of the above (a through c) are true
e. only a and c above are true; bankfull discharge occurs infrequently on most streams,
perhaps once every 15 to 25 years
16. How are floodplains formed?
a. almost entirely by overbank deposition of silt and clay during floods
b. mostly by a combination of erosion on the outside of bends and deposition of gravel and
sand as point bars on the inside, along with some overbank deposition of finer materials
c. almost entirely by erosion, i.e., by the back-and-forth planing effect of the river
d. mostly by large-scale scour of low areas near the river during floods
e. mostly by meanders being cut off and then filling with swamp and lake deposits
17. If a river has a braided pattern, which of the following statements about it are likely to be
true? (Mark statements T or F, then choose answer)
___the channel is likely to be relatively stable (i.e. changes position relatively slowly)
___the stream has very easily erodible banks
___the stream is carrying a heavy and very coarse sediment load
___the channel bed has a relatively steep slope
___the stream carries most of its load in suspension
The correct matching order is:
a. TFFFT b. FFFFF c. FTTTF d. TTTTT e. TFTFT
18. You are looking for some property where you can drill a well
and get a good, reliable water supply. Which materials below
would probably provide the poorest supply. Circle choices as
you go, then choose answer.
1. very highly jointed and fractured volcanic rock
2. outwash gravels from a continental glacier
3. lake sediments
4. fine-grained, compact glacial till
5. greywacke sandstone
a. 1 and 2 b. 3 and 4 c. 2 and 5 d. 1 and 4 e. all of them would provide poor supplies
Questions 19 and 20 refer to the map belowThis map shows the elevation of the water table by means of contours on it (dashed lines). The elevation of the land surface is shown by topographic contours (solid lines). 19. Which direction is the groundwater flowing?
a. NW to SE b. SW to NE c. NE to SW d. SE to NW e. you cannot tell from such a map
20. If you were drilling a well at point B, about how many feet
down would you have to drill before you hit water?
a. 500 feet b. 230 feet c. 730 feet d. 270 feet e. you cannot tell from this sort of map
21. A rock with high porosity and high permeability would
a. provide little storage but transmit water easily
b. provide much storage but transmit water poorly
c. provide little storage and transmit water poorly
d. provide much storage and transmit water easily
e. the question is impossible: rocks of high porosity
always have low permeability22. How does an earthflow differ from a debris flow?
a. earthflows are slower moving than debris flows b. earthflows involve less water and are more 'viscous' than debris flows c. earthflows have a more hummocky, lobate appearance than debris flows d. earthflows are less likely to cause catastrophic loss of life than debris flows e. all of the above answers (a&endash;d) are correct
23. If you wanted to stabilize a large landslide, which of the things listed below would
probably be most effective?
a.loading the top of the slope to increase friction b.steepening the slope so that the water runs off faster c.cutting down trees on the landslide to remove their weight from the slope d.installing drains to drain water out of the rock and thus reduce pore pressures e.none of the above will be effective&endash; all will increase the chance of landsliding
24. Mount Olympus on the Olympic Peninsula of Washington is glaciated while many higher peaks in
the Rocky Mountains at the same latitude are not because Mt.Olympus:
a.is steeper b.has bigger south-facing slopes c.is in an area of much higher precipitation d.is colder e.once had continental glaciers butting up against it and these left pieces of themselves behind
25. Which of the following landforms is not the result of glacial erosion?
a. cirques b. fjords c. U-shaped valleys d. drumlins e. hanging valleys
26. Of the features listed below, which can be associated with both continental (ice sheet) and
valley (mountain) glaciation? (Circle correct features as you go, then pick answer.)
1) cirques 2) eskers 3) highly scoured bedrock 4) erratics 5) drumlins 6) tall, very steep-sided morainal ridges 7) grooves and striations a. 1 and 6 b. 2 and 5 c. 3, 4, and 7 d. none of the above indicate continental glaciation; all indicate valley glaciation e. all of the features are highly indicative of continental glaciation
Answers (with reasoning):
1. b (In a cool temperate climate, the water tends to be acidic. Quartz is stable
in acidic water and hence will weather very slowly. It will produce little
or no clay. All the other rocks contain aluminum or iron-bearing minerals [such
as feldspar and pyroxene] which are attacked by acidic water and weathered to clay.)
2. d (The minerals in the gabbro are high in aluminum and iron. In the tropics the
water tends to be neutral; this causes the silica to be leached, while the
iron and aluminum oxides and hydroxides formed by weathering are stable and
remain in the soil, forming laterites or bauxite.)
3. a (In a desert, the dryness means that chemical weathering will be slow and
physical breakdown -- perhaps granular disintegration due to expansion of
biotite grains-- will predominate.)
4. d (In the cool forested temperate climate, water would tend to be acidic.
Limestone dissolves readily in acidic water, hence will weather [by solution]
the fastest.
To answer questions 5- 10 you must be able to interpret the graph. It shows how the total amount
of water infiltrated into the soil varies with time after the beginning of rain.
5. d (Line 4 represents a soil that infiltrates very little water. After 140 minutes only about
2 inches have been infiltrated. Clays have low infiltration capacities.)
6. a (Line 1 represents a soil that has a high infiltration rate at the beginning, and whose
infiltration rate stays nearly constant -- and high-- with time. Gravels and coarse
sands have high infiltration rates.)
7. a (Heavy vegetation -- especially forest-- protects the soil from sealing by raindrop
impact and keeps infiltration rates high. Line 1 starts off high, and since its slope
is nearly constant, it shows that the infiltration rate is changing very little with
time, suggesting good protection.)
8. c (Line 3 starts out high, and then quickly flattens off showing that relatively little
more water is being infiltrated. This is what you'd expect if a clay soil had open
cracks in it--which would admit water easily-- at the beginning, and then the cracks
closed up as the clays swelled.)
9. a (For a septic-tank drain field you need a material that passes water easily -- preferably
a sand or gravel. See answers to question 5 and 6 for reasoning.)
10. d (The soil represented by line 4 has the lowest infiltration rate at all times.)
11. a (Barren rocky areas have low infintration rates because of the lack of vegetation and
the poorly permeable rock. Thus most of the rainfall runs off over the ground surface
as Horton overland flow.)
12. b (Runoff = rainfall - evapotranspiration loss - groundwater outflow: 70-35-10 = 25)
13. d (As the forest regenerates, more water will be lost through evapotranspiration, thus
reducing the streamflow.)
14. c (Where the infiltration rate is high, less water will run off over the ground surface as
overland flow, and so surface erosion by wash and rilling will be reduced. All the other
choices will reduce infiltration rate, and thus promote overland flow and erosion.)
15. d (Question is self-explanatory)
16. b (Question is self-explanatory)
17. c (Braided streams tend to have easily erodible banks and carry a large amounts of mostly
coarse sediment, which moves by bouncing and rolling dowen the bed, i.e., as bedload.
The channels are wide and shallow, with steeper longitudinal gradients.)
18. b (Lake sediments and fine-grained compact glacial till will both be
clay-rich and thus have very low permeabilities. To get a good
supply you need materials with high permeabilities.)
19. b (Draw lines at right angles to the water-table contours; flow will
be along these lines from high water table elevation to low wt elevation)
20. d (The ground surface elevation at B is approx. 500 ft, while the
wt contours show that its elevation is about 230 ft. The depth
to water is thus 500-230 = 270 ft.)
21. d (Porosity measures the storage capacity of a material; the higher the
porosity, the more water can be stored. Permeability measures the
ease with which water can move through the material; the higher the
permeability, the more easily the water can be transmitted through it.)
22. e (Refer to basic descriptions of earthflow and debris flow.)
23. d (Draining water reduces pore pressure and increases stability by increasing the
frictional strength of the earth materials. All the other suggestions will
decrease slope stability.)
24. c (Glaciers will form wherever the winter accummulation of ice and snow exceeds the
amount lost by melting and evaporation in the summer. Because the Olympics get
a huge amount of snowfall -- think of the Olympic rainforests at lower elevations--
they have developed glaciers.)
25. d (Drumlins are formed by continental glacier deposition, not erosion.)
26. c (Cirques and steep-sided morainal ridges are associated only with valley glaciers;
eskers and drumlins are associted with continental glaciers. Both kinds of glaciers
can scour and groove bedrock.)