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Homework for Lecture 4
ES 1000
Use these questions to test your knowledge of Lecture 4.
A. Short answer:
1. When hot particles within a nuée ardente fall to the ground and stick
together, a welded _____ forms.
2. A flow of mud and pyroclastic material is called a ________.
3. A volcanic dome forms when rising ________ cools and hardens within a
volcano’s crater.
4. Pyroclastic materials that cool and solidify from lava ejected into the
atmosphere are called _________.
5. When basaltic lava erupts beneath the sea, it forms a ________ structure.
6. A volcano with a composite cone has layers of _______ and layers of
pyroclastic material within the cone.
7. Volcanoes that form on continent margins above subduction zones
typically have _______ silica than volcanoes in rift valleys.
8. Within a single lava flow in Hawaii, a'a' textured lavas are found ______
_______ from the vent than pahoehoe lavas.
9. Composite cones usually have __________ lava.
10. Volcanoes are created when molten rock escapes from the earth's interior
through surface openings called _________.
B. Match the terms
1. Shield Volcano
_____
a. magma chamber collapsed
2. Lahar ______
b. an andesitic, composite volcano
3. water vapor, carbon dioxide____
c. is silica-rich and/or cool
4. Nuée ardente ____
d. ropy lava
5. Pillows ____
e. has highly eroded slopes
6. Mount St. Helens _____
f. made of hot ash and gasses
7. Caldera _____
g. underwater lava structure
8. Very viscous lava
h. gasses expelled by volcanoes
9. Possibly extinct volcano
i. typical volcano type forming Hawaii
10. Pahoehoe
j. mudflow
C. True or False?
1. A very viscous magma tends to be less explosive. True or False?
2. The most quiet and least dangerous volcanic eruptions involve
glowing avalanches of volcanic rock fragments called Nuée ardente.
True or False?
3. Basaltic magmas are hotter than, and contain less silica than,
andesitic magmas. True or False?
4. Basaltic magmas are less viscous than andesitic magmas and can
get to the surface more easily. True or False?
5. Magmas of gentle volcanoes have a higher silica content and a
higher viscosity than magmas of violent volcanoes. True or False?
6. Violent volcanoes often occur at convergent plate boundaries,
whereas gentle volcanoes often occur at divergent plate
boundaries. True or False?
7. Violent volcanoes are low in silica; gentle ones are high in silica.
True or False?
8. Tephra may consist of sizable blocks of solidified lava known as
volcanic bombs. True or False?
9. Pyroclastic eruptions usually occur along transform boundaries.
True or False?
10. Hawaiian volcanoes are thought to be formed by magma plumes
rising from deep in the mantle. True or False?
D. Multiple choice:
1. All of the following events could indicate an impending eruption
EXCEPT:
(a) discovery of new hot springs around the volcano. deleted
(b) a measurable bulge or swelling of the volcano.
(c) swarms of small earthquakes in the region.
(d) a highly eroded, volcanic peak.
2. A volcano can release several kinds of gases into the air, but most of the
gas is:
(a) water vapor and carbon dioxide
(b) argon and sulfuric acid.
(c) nitrous oxide and chlorine.
(d) fluorine and carbon dioxide.
3. The term viscosity refers to:
(a) how heat and pressure influence a liquid’s gas content.
(b) a liquid’s resistance to flow.
(c) how dense a liquid is.
(d) how a liquid moves upward against gravity.
4. Of the following, the magma with the highest viscosity would have:
(a) a high silica content and high temperature.
(b) a high silica content and low temperature.
(c) a low silica content and high temperature.
(d) a low silica content and low temperature.
5. Compared to andesitic lavas, basaltic lavas tend to be:
(a) higher in viscosity and they retain dissolved gases.
(b) higher in viscosity but they easily release dissolved gases.
(c) lower in viscosity and they retain dissolved gases.
(d) lower in viscosity and they easily release dissolved gases.
6. Which of the following is LEAST likely to be a product of a basaltic
volcano?
(a) Columnar jointing.
(b) Nuée ardente.
(c) Pahoehoe lava flow.
(d) ‘A‘a lava flow
7. Which of the following is a likely product of an underwater basaltic
eruption?
(a) Nuée ardente
(b) Lahar
(c) Pillow lavas
(d) Pumice.
8. Felsic magmas with high water and gas content commonly form:
(a) pahoehoe.
(b) ‘a‘a.
(c) columnar jointing.
(d) pumice.
9. Which of the following is LEAST likely to be a product of a pyroclastic
volcano?
(a) Lahar.
(b) Nuée ardente.
(c) Volcanic bombs.
(d) Extensive lava flow.
E. Short answers Describe the differences between basaltic and andesitic
volcanoes. Your file Igneous Rock Summary.doc will help you.
Be sure to include:
1. a. How their magmas differ in silica content,
b. how their magmas differ in temperature,
c. and how the magmas differ in viscosity.
2. a. How viscosity controls their differing ability to give up gasses,
b. how trapped gasses control the explosiveness of their eruptions.
c. and how they differ in their products, i.e. their lavas and
pyroclastics. Which have basaltic pahoehoe and a'a' lavas, which have
commonly have lahars and andesitic nuée ardente?
3. Given the above information, explain which type is dangerous, and
which is not very dangerous, and why?
4. Explain how basaltic and andesitic volcanoes differ in typical plate
tectonic settings. You should include in your discussion mid-ocean
ridges, plumes such as that forming Hawaii, and volcanic arcs caused by
subduction zones.
5. Be sure to copy Igneous Rock Summary.doc into your notes.
F. As always, for calculations, show all work.
1. Read slides 1-14 in Lecture 13 Observations. Then do the problem below.
The value for the mean will vary slightly from your Homework 02-3. Use
the value 1.002g/cc given here.
SAMPLE STANDARD DEVIATION s
The sample standard deviation s is a measure of the spread of our data
around the mean,
We will take this step by step.