Geology 141
Autumn, 1998
Name
.
9 October, 1998
GE141: PHYSICAL GEOLOGY
FIRST HOUR EXAMINATION
INSTRUCTIONS: Please read all instructions and questions CAREFULLY and
completely. If you do not understand a question as it appears on the exam, PLEASE ASK
FOR CLARIFICATION!!! It is to YOUR benefit to do so. This examination is worth
125 points, or 12.5% of your overall semester grade. Exams will be graded as quickly as
possible; your individual point total will be entered on the last page to ensure that only you
know how well you did on the exam, unless you choose to divulge that information to
others.
"You will find out that there are all sorts of ways
of learning, not only from people and books, but
from sheer trying."
- Gertrude Jekyll
Geology 141: Autumn, 1998
First Hour Exam
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Section I: Multiple choice. Please circle the letter of the response that is correct or that BEST
answers the question or completes the statement. There is ONLY ONE BEST ANSWER for
each question. Each question is worth 3 points; this section is worth 75 out of the total of 125
for the exam.
PLEASE READ EACH QUESTION AND RESPONSE CAREFULLY!
1. The most abundant two elements in the Earth's crust, comprising some 74% of the entire crust of
the Earth by weight, are
a. oxygen and iron
d. oxygen and silicon
b. iron and nickel
e. nickel and silicon
c. iron and aluminum
2. The continental crust of the Earth is typically about how thick?
a. about 1-2 km
c. about 10-35 km
e. about 1200 km
b. about 5-8 km
d. about 40-70 km
f. about 2900 km
3. The continents are much higher than the ocean basins because
a. they are being pushed up by mantle plumes and convection cells.
b. they are composed of less-dense rocks than the oceanic crust.
c. volcanoes on the continents have erupted vast thicknesses of volcanic
rocks, so they're much thicker than the crust beneath the oceans.
d. the continents are composed mainly of sedimentary rocks, while the
oceanic crust is composed mainly of metamorphic rocks.
4. The magnetic field of the Earth is believed to be produced by
a. flow of magmas in the upper mantle and convection cells
b. flow of the liquid outer core around the solid inner core
c. chemical reactions between iron, silicon and oxygen in the mantle
and the core
d. the effects of cosmic radiation on the minerals of the crust.
5. The difference between the inner and outer core is that the
a. inner core is liquid, while the outer core is solid.
b. inner core is solid, while the outer core is liquid.
c. inner core is composed of iron and nickel, the outer core is silicates.
d. inner core is dense iron oxides, while the outer part is molten iron.
6. The ONLY non-silicate minerals that are critically important as rock-forming minerals in the
Earth's crust are the
a. oxides and hydroxides
d. native elements
b. sulfides
e. phosphates
c. carbonates
f. sulfates
7. Over half the Earth's crust, by weight, is composed of what group or subgroup of minerals?
a. feldspars
d. carbonates
b. oxides
e. sulfides & sulfates
c. sheet silicates
f. native elements
Geology 141: Autumn, 1998
First Hour Exam
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8. The classification of all rocks into three major groups is based on their
a. mode of origin
c. silica content
b. mineral composition
d. relative densities
9. How readily a magma will flow, how a volcano will erupt, and the ultimate shape of the volcano,
are ALL a result of all of the following factors EXCEPT
a. temperature
c. silica content
b. volcano age
d. dissolved gas content
10. The two most common gasses in magmas are
a. hydrogen and oxygen
d. steam and carbon dioxide
b. helium and hydrogen
e. steam and silicon dioxide
c. methane and carbon dioxide
f. ammonia and carbon dioxide
11. Most of the active volcanoes in the world are found
a. in Hawai'i, the Galapagos, Iceland, and other oceanic islands.
b. in the Mediterranean Sea region (Italy, Greece, Turkey, etc.).
c. in Africa, the Himalaya, and the Arabian Peninsula.
d. on the margins of the Pacific Ocean.
12. Sills (like the Palisades Sill in New York) are
a. igneous intrusions that outcrop over an area greater than 100 km2
b. igneous intrusions that outcrop over an area less than 100 km2
c. tabular intrusive bodies that cut across pre-existing rock units.
d. tabular intrusive bodies that intrude between pre-existing layers.
e. naturally occurring ridges that look like window frames.
13. The area beneath and surrounding Mt. Katahdin in Maine's Baxter State Park is underlain by
granite over an area of more than 600 square kilometers. This geologic unit is therefore called
the
a. Katahdin Stock
c. Katahdin Dike System
b. Katahdin Batholith
d. Katahdin Lithograph
14. Olympus Mons on Mars is a broad shield volcano, 600 km across at the base and some 20 km in
total height. It was derived from repeated eruptions of
a. extremely hot, low-silica magmas
b. extremely cool, low-silica magmas
c. extremely hot, high-silica magmas
d. extremely cool, high-silica magmas
15. A typical granite is formed from a magma that in turn is derived from
a. melting of pre-existing high-silica rocks in continental crust.
b. melting of pre-existing low-silica rocks in oceanic crust.
c. molten reservoirs of magma deep within the mantle.
d. high-silica sources located in the outer core.
e. low-silica sources located in the inner core.
f. unknown sources that occur randomly throughout the Earth.
Geology 141: Autumn, 1998
First Hour Exam
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16. The minerals at the very top of Bowen's Reaction Series are those that have relatively low silica
contents, and will first begin to crystallize at
a. relatively high temperatures
c. relatively low temperatures
b. intermediate temperatures d. any temperature
17. Among the minerals in Bowen's Reaction Series, those that will most quickly break down
(chemically weather) in soils are
a. those at the very top, like olivine and calcium plagioclase
b. those in the middle, like hornblende and sodium plagioclase
c. those at the bottom, like quartz and muscovite
d. Bowen's Reaction Series cannot predict which minerals will weather
most readily in a soil.
18. Typical mechanical weathering processes include all of the following except
a. ice wedging
d. root wedging
b. hydrolysis
e. salt wedging
c. salt hydration
f. thermal expansion
19. A quartz-rich sand on a beach is cemented together by clays and iron oxides. Over time, it is
buried, and then pushed by tectonic processes deep into the Earth. Ultimately, it gets so hot that
it melts. When it recrystallizes, it is now a (an)
a. sandstone
c. chert
e. chemical sedimentary rock
b. limestone
d. igneous rock
f. clastic sedimentary rock
20. The highest rate of chemical weathering as well as the most biological activity will be found in
which soil horizon?
a. A horizon
c. C horizon
b. B horizon
d. unaltered parent material
21. Sedimentary rocks that are comprised of the bits and pieces of pre-existing rocks are called
a. chemical sedimentary rocks
c. clastic sedimentary rocks
b. biogenic (organic) sedimentary rocks
d. metamorphic rocks
22. A sedimentary rock with essentially no minerals, derived from plant matter that accumulated
under non-oxidizing conditions, is
a. chert
c. limestone
e. shale
b. coal
d. flint
f. gypsum
23. "Rock salt" is a rock comprised mainly of the mineral halite, which accumulated in some areas to
great thicknesses by
a. evaporation of large amounts of water, which left the salt behind.
b. deposition of salt crystals in lakes by streams that eroded them from
rocks in the surrounding environment.
c. crystallization from high sodium, high chlorine magmas in desert
regions.
d. processes that geologists still have yet to figure out.
Geology 141: Autumn, 1998
First Hour Exam
24. Flocculation is a process whereby
a. minerals in a magma crystallize out at different temperatures,
yielding rocks with many different grain sizes in them.
b. clays in suspension in waters clump together due to the presence of
salt, and settle more rapidly than they would otherwise.
c. sediments of different grain sizes are sorted in the natural
environment, so that sands wind up in some areas while clays go
elsewhere.
d. chemical and mechanical weathering of rocks takes place at roughly
equal rates in the rock.
25. Which of the following is NOT a source of metamorphism in rocks?
a. being "baked" by an igneous intrusion
b. having hot, mineral-rich fluids flow through the rock
c. being buried to depths of tens of kilometers by plate tectonic activity
d. being melted by an intense local heat source
e. being ground to a powder and then re-cemented in a fault zone.
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Geology 141: Autumn, 1998
First Hour Exam
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Section II: Short answers, fill-ins, etc. Please respond to each question in the most appropriate
fashion. Please make your responses concise and to the point, but thorough. There should be
ample space provided for an adequate response; PLEASE RESTRICT YOUR RESPONSES
TO THE SPACE PROVIDED. PLEASE ALSO write legibly; I CANNOT give any credit for
responses I can't read! The number of points for each question is indicated in parentheses
after the question; there are 50 points possible for this entire section.
26. What is the critical difference between chemical weathering and metamorphism? (10 points)
27. The five most important factors that determine the ultimate character of a soil are:
1 point each)
(5 points,
28. What is the critical difference between chemical and mechanical weathering in rocks? (10 points)
Geology 141: Autumn, 1998
First Hour Exam
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29. (a) Sketch and label an example of a silica tetrahedron (5 points; 2-3).
(b) Why are silica tetrahedra important in geology? (5 points)
31. On the maps on the following page (the maps are printed back-to-back), locate precisely each of
the following localities or features. FOR SMALL FEATURES OR LOCALITIES, use a sharp
arrow drawn from your label to the feature, so there can be no doubt about what you are
labeling. (10 points, 1 point each)
All labels must be correctly spelled for credit!
[ Since all you have to do is copy it from the list below! ]
On the map of the U.S.:
Washington, D. C.
Lake Michigan
Montana
New Mexico
San Francisco Bay
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On the map of the world:
Andes Mountains
Alaska
Java
Kamchatka
Zaire (= Democratic Republic of
Congo)
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Grade on exam: __________________ out of 125 possible*.
* If this is below 88, please see me within the next week !!!
NOTE: After exams are graded, I will return your exam ONLY to you. It will not be released to friends,
roommates, your lab partner, or anyone else.