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study help
earth sciences
geology
Questions and Answers of
Geology
Meteorites provide scientists with clues to the nature of the earth’s interior. How?
Is the magnetic field of the earth (Fig. 1.6) generated internally or externally?
What is the evidence that the earth’s magnetic field is not emanating from permanently magnetized material, even though it might seem that the earth has a strong bar magnet at its center?
If earth’s magnetism is not derived from a permanently magnetized solid metallic core, what causes the magnetism?
Drill holes into the earth’s crust indicate a relationship between temperature and depth. What is this relationship?
At the rate of temperature increase given in Problem 1.40, how hot is the center of the earth?
Calculate the vertical exaggeration of Fig. 1.3
Calculate the vertical exaggeration of Fig. 1.4.
The size of the earth was probably first calculated by Eratosthenes, a Greek living in Egypt, in 250 B.C. Figure 1.7 shows the elements he used in his calculation. How could he have arrived at a
How was it first determined that the earth is not perfectly spherical?
The three main types of volcanoes are illustrated in cross-section in Fig. 3.5. Note scales. Name each type.
What are the differences in composition of the two major types of magma?
How does the chemical composition of a magma affect its viscosity (fluidity)?
Why are there three main types of volcanoes?
Bowen’s idea of fractional crystallization of basaltic magma as a means of producing the broad variety of igneous rocks, while certainly a natural and laboratory process, does not completely answer
What are some other theories which explain why there are different kinds of magma?
What is the source of the basaltic lavas of the midoceanic ridges?
Basaltic volcanism does not tend to be highly explosive because of the low viscosity of the magma. Yet, the basaltic volcano Surtsey which formed off of Iceland on the Mid-Atlantic Ridge in 1963 was
Is an igneous rock likely to be composed only of quartz and olivine? Why or why not? (Refer to Fig. 3.3.)
If, as a mafic (basaltic) magma crystallizes (Figs. 3.3 and 3.4) underground, the crystals are removed from contact with the magma, and the remaining magma crystallizes separately, which kind of a
If a magma crystallizes at a temperature of about 1500°C, what is its likely composition— felsic or mafic? (See Fig. 3.3.)
How does the rate of cooling of a magma affect grain size of the resultant rock, and why? (See Fig. 3.4.)
See the microscopic view of igneous rocks in Fig. 3.6. Which rock cooled the slowest and which cooled the fastest?
How does a porphyritic rock, as in Fig. 3.6(b), form?
Name another factor, other than the rate of cooling, that can affect crystal size. Very coarse-grained intrusions of igneous rocks (pegmatites) are an example of this factor at work.
Why do many of the late-forming pegmatites of the previous question contain rare elements such as lithium, tin, and beryllium?
What kind of igneous rock bodies are the light-colored rocks shown in Fig. 3.7?
A layer of granite 1 m thick is present in a sequence of sedimentary rocks, parallel to the bedding in the sedimentary rocks (Fig. 3.8). Is it a dike, a sill, or a stock?
Refer to the previous problem. How can one tell whether it is a sill which intruded between rock layers or whether it is a lava flow which was extruded on top of sedimentary rock and then was covered
What is the most obvious evidence that lava extruded under water?
Figure 3.9(b) depicts a pile of pillows tilted to a vertical position. In which direction are the pillows topping (that is, which is the top of the sequence?)
Figure 3.2 shows the locations of the world’s active volcanoes, is a volcano likely to suddenly appear in, say, Iowa or Minnesota?
Igneous rocks are classified on the basis of texture (grain size) and composition (mineralogy). A general indicator of igneous rock composition is the color. Name the following igneous rocks by
Why was obsidian a much sought after rock which was traded far and wide by the Native Americans? (For example, obsidian from Yellowstone Park was traded as far east as Ohio.)
What coarse-grained (plutonic) rock consists of abundant calcic plagioclase plus olivine and pyroxene?
What is the fine-grained equivalent of gabbro?
Name the coarse-grained (plutonic) rock consisting primarily of hornblende and sodic plagioclase.
What is the volcanic rock which has the same composition as a granite?
What are the two most abundant igneous rocks?
What are the rounded structures shown in Fig. 3.10?
How would one distinguish between an amygdaloidal basalt and a porphyritic basalt?
Volcanoes are classified as active, dormant, or extinct. If they have erupted during the last 50 years, they are clearly classified as active. On what bases are dormant or extinct volcanoes
Mt. Somma (ancestral Mt. Vesuvius), which towered above the Roman seaside resort cities of Pompeii and Herculaneum, hadn’t erupted for 800 years, when in A.D. 79, it erupted. What happened to the
What were the major geologic effects of the May 18, 1980, eruption of Mt. St. Helens in southwestern Washington (Fig. 3.11)?
Note the similarities in the sketches of Mt. St. Helens (Fig. 3.11) and Crater Lake, Oregon (Fig. 3.12). Surmise how Crater Lake may have formed.
What could happen to the cities shown in Fig. 3.13 if any of the nearby volcanoes erupted?
How do geologists determine whether hot ash flows (glowing avalanches) were minor or major events?
Figure 3.14 is a sketch of lava flows in the Columbia Plateau region of northwestern United States. What do the flows indicate about the viscosity and composition of the lava?
Note the map of major igneous rock bodies along western North America (Fig. 3.15). Name the type of igneous bodies shown, and name the likely dominant rock type present.
Figure 3.16 includes three sketches of the Hawaiian Islands. (a) What is the origin of the islands? They are volcanoes
Refer to Fig. 3.16. What is the viscosity and composition of the lavas which formed Hawaii?
Refer to Fig. 3.3 Which has been introduced as the order of crystallization of minerals out of a mafic magma. More specifically, it is known as Bowen’s Reaction Series, with one side depicting
Note the columnar joints in igneous rocks in Figs. 3.14 and 3.17. What causes them to form, and how are they oriented relative to the shape of the body?
What minerals commonly fill vesicles to form amygdules as in Fig. 3.10?
If volcanoes are dangerous, as illustrated when Mt. St. Helens erupted in May 1980, why are some volcanic regions such as Sumatra in the East Indies so densely populated?
What are the two main types of weathering?
What are the agents of mechanical weathering
What causes chemical weathering?
In which type of climate is chemical weathering most effective?
Do mechanical and chemical weathering operate independently of each other?
Why is mechanical weathering so important to chemical weathering?
Joints, or cracks in rocks, are natural passageways for air and water. What should happen to joints with time? See Fig. 4.2.
How might the big rounded granite “boulders” in Fig. 4.3 have formed? (Clue: They have been formed at this site and have not been carried here by ice, water, or humans.)
How are talus piles below cliffs, as in Fig. 4.4, related to weathering?
Which minerals does the chemical weathering process called oxidation affect most readily?
What are the common products of oxidation?
Which chemical weathering processes are most important in the production of clay minerals?
Explain carbonation.
Give a generalized chemical equation that illustrates the effect of carbonation on limestone, the common sedimentary rock made of the mineral calcite (CaCO3).
Give a generalized chemical equation that illustrates the effect of carbonation on silicate minerals.
Explain hydrolysis.
When a biotite granite weathers in a temperate climate, what products remain to form the soil?
When a biotite granite weathers in a temperate climate, what cations may be carried away to the ocean?
Are all the ions listed in the previous problem carried away to the ocean and hence lost to the soil?
What is the order of chemical stability of the common igneous minerals?
Which igneous mineral is the most stable, both mechanically and chemically?
Which mineral, quartz or olivine, should be most abundant in beach sands?
Which rock should be most resistant to chemical weathering—gabbro or granite?
What is the most important factor in the production of good soils—the climate, the topography, or the rock type?
Why are the best clay minerals, and hence the best soils, formed in temperate climates?
Why are the soils in the tropics generally poor soils?
Why are clay minerals essential for a good soil?
What are the products of chemical weathering in a subtropical to tropical climate?
Why are so many soils yellow, brown, or red in color?
Why are some soils black?
Where in the world are the high-protein plants grown and why?
If subtropical and tropical climates produce poor soils, can any good come of the intense chemical weathering? (See Problem 4.28)
What is soil?
Describe a typical soil profile.
Which rock should be most resistant to chemical weathering in, a temperate climate—a granite consisting of the igneous minerals quartz, orthoclase, and biotite or a red shale consisting of clay
Explain the difference between weathering and erosion.
If you want your tombstone to survive a long time as a legible monument to your greatness, should you request that it be made of marble (a metamorphic rock consisting of calcite), or slate (a
What is spheroidal weathering?
What is exfoliation?
Weathering affects the topography of the earth’s surface in a broad and important way. How?
What may be the most important geologic process on earth?
What mineral group is most abundant in igneous rocks, and why is its abundance so Important to people?
Which other elements, besides iron, are commonly oxidized?
Why is the order of weathering of the common igneous minerals the same as Bowen’s reaction series (see Problem 4.20)?
How does the industrial revolution, with its output of CO2 (carbon dioxide) from the burning of coal and petroleum affect chemical weathering?
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