Geology 208
Spring 2011
Name__________________
Midterm Exam—Take-home part
Your answers to the questions below should be typed (double spaced please), written in
complete sentences and paragraphs, and submitted by 11:00 AM on May 3. You may
talk with others in the class about ideas, but your explanations must be your own. One
way to insure this is to only talk with others and then write and explain your answers by
yourself.
1. For each of the photographs below, determine if each statement about the picture is
possibly true or definitely false. (3 points each)
If the statement is possibly true, explain what additional data you would need from the
site to confirm your conclusion.
If you believe the statement is false, explain why it is false. (I suggest looking at these
images on the course web site).
a) The sediment indicated by the arrow in
the photo to the right is glacial till from the
Vashon advance.
b) The sediment pictured in this photo is a
lahar from Mt. Rainier
c) The sediments illustrated in this photo
were deposited in an ice-marginal lake
during the Vashon advance
d) The photo to the right is glacial outwash
from the Orting drift
2. At the end of the Vashon glaciation, the valley where downtown Auburn and Kent are
located today was a part of Puget Sound. Discuss how the valley we call the Green River
Valley geologically evolved after the Vashon glaciation. (10 points)
3) (14 points total) What is the evidence:
a) that the catastrophic floods of eastern Washington were due to the draining of
glacial Lake Missoula?
b) that there was more than one catastrophic flood over eastern Washington?
c) The USGS CVO web site states the following in reference to the Channeled
Scablands floods of eastern and central Washington:
“With flood waters roaring across the landscape at speeds approaching 65 miles per hour,
the lake would have drained in as little as 48 hours.”
http://vulcan.wr.usgs.gov/Glossary/Glaciers/IceSheets/description_lake_missoula.html)
What physical evidence could you use to determine if the statements made in this
quotation are accurate? Explain your ideas.
4. (14 points total) The stratigraphic section
to the right is from the northern end of the
Puget lowlands. Use the descriptions of the
layers given below to:
a) determine the environment of
deposition (or process) for each of
the layers
b) in what ways is this sequence of
layers similar and different that the
layers we discussed from Discovery
Park (the Seattle section we covered
in class)
Data for layers illustrated above:
Layer 1- cross-bedded sands, silts, pumiceous sand, and peat
Layer 2- diamicton composed of gravel and boulder down to clay. Compact, stands as a
cliff. Clasts have moderate weathering. Rock types include basalt, granite, chert,
greenstone (metamorphosed basalt).
Layer 3- very similar to layer 2 in structure and composition; however this layer has
marine clam fossils. Dates on this layer indicate that it is about 80,000 years old.
Layer 4- cross-bedded sands, silts, and clays and peat. Dates from this layer indicate it is
about 25,000 years old
Layer 5- cross-bedded sands and gravels. Rock types in the gravels include northern
sources areas
Layer 6- compact diamicton- boulders to clays—stands as a steep bluff. Clasts are hard
and show very little weathering. Rock types indicate a northern source
Layer 7- diamicton, but not as compact as layer 6. Clam fossils, rock types include
granite, basalt, chert, gneiss
Answer two questions from questions 5-8: (Please give the number of the question so that
I know exactly which question you are answering.) (10 points each for a total of 20)
5. In what ways is the history of volcanism in the Snake River Plain/Yellowstone region
different than the volcanism in the Cascade Range? Explain reasons that could explain
these differences.
6. The photograph below is the along the north side of Mt. Mazama seen from Crater
Lake. A dike is illustrated cutting through older lava and ash layers. The dike becomes a
layer that is labeled as “sill or lava flow”. Imagine that you could climb up the side of the
caldera and examine the contact relationships of these layers. What specific data would
you accumulate that would help answer whether the layer in question is a lava flow or a
sill? The more well explained ideas you have the better. (I am not asking whether it is a
sill or a lava flow, just how you would determine the answer.)
7. Oregon volcanoes such as Thielsen, North Sister, and Mt. Washington have a similar
pattern of development. What is this pattern and explain how this pattern may have
developed.
8. Compare and contrast “your” volcano (the volcano you discussed in class) with Mt.
Rainier.