Midterm #2 Questions

Question 1

The majority Earth’s volcanic activity occurs in which of these tectonic settings?

Answer 1

• spreading centres

Question 2

The volcanoes of the Cascade Range, including Mr. Garibaldi in British Columbia and St. Helens in Washington, result from ____.

Answer 2

• the subduction of the Juan de Fuca plate beneath North America

Question 3

Volcanoes in Canada result from ____.

Answer 3

• a hot spot
• subduction
• rifting

Question 4

The more than 200 dormant valances in Canada are concentrated in ____.

Answer 4

• British Columbia and Yukon

Question 5

Mount Garibaldi in southwest British Columbia is a ___.

Answer 5

• stratovolcano

Question 6

Ways of generating pyroclastic flows include ___.

Answer 6

• overspilling of crater rim at Mount Pelee, 1902-1903
• dome collapse as at Mt. Unzen 1991
• eruption column collapse at Mt. Mayon, 1968
• direction blast as at Mt. St. Helens, 1980, and Mt. Pinatubo, 1991

Question 7

In August 1986, a gigantic volume of CO2 belched forth from Lake Nyos in Cameroon and swept down the adjacent valleys asphyxiating 1700 people. The origin of this gas was ___.

Answer 7

• a basaltic magma in the subsurface

Question 8

Several geologic phenomenas are being studies as signs of an impending volcanic eruption. These include seismic waves, ____, and the release of gases.

Answer 8

• ground deformation

Question 9

If a volcanologist installs a sensitive seismometer besides a volcano and it detects longer-period seismic waves this means that ____.

Answer 9

• magma eruption is imminent

Question 10

Southwestern British Columbia and the Pacific Northwest region of the United States (Washington and Oregon) have long-term risk for both explosive volcanic eruption and earthquake. (True or False)

Answer 10

• true

Question 11

The chain of volcanoes in the Cascade Range like those of the Hawaiian Chain located above a hot spot, vary in age from young to old in an orderly progression. (True or False)

Answer 11

• False

Question 12

The Indonesian word Lahar refers to the buoyant ash plume associated with Plinian type eruptions. (True or False)

Answer 12

• False

Question 13

Haze can produce a cooling effect on Earth while excess of carbon dioxide causes warming. (True or False)

Answer 13

• True

Question 14

Volcanic eruptions are relatively peaceful above continental hot spots, such as Hawaii while eruptions above oceanic hot spots such as Yellowstone National Park may be very explosive.

Answer 14

• False

Question 15

Wind caused waves undergo changes when they move into shallow water near the shoreline. Friction with the floor of the shallow water results int eh orbits of the water molecules at the bottom of the wave to become more

Answer 15

• elliptical

Question 16

When wind caused waves approach the shoreline, friction causes them to show their wavelengths to ___ resulting in waves ____.

Answer 16

• decrease, growing taller

Question 17

Tsunamis typically have ___ relative to wind-blown waves.

Answer 17

• long periods and long wavelengths

Question 18

Tsunamis wavelengths can be as great as ____.

Answer 18

• 800 km

Question 19

Which of the following best describes what happens to tsunami waves as they move from the open ocean and towards the shallow water near the shore of the coastline?

Answer 19

• the waves increase in amplitude and decrease in velocity

Question 20

Tsunamis arrive as a series of several waves separated by periods typically in the ____ range.

Answer 20

• 10-60 minutes

Question 21

A sailor tells you that he once experienced a huge tsunami while sailing int eh Pacific Ocean several hundred miles from any landmass. You are sceptical because ____.

Answer 21

• tsunamis are rarely felt in deep water because they have long wavelengths and low heights.

Question 22

Tsunamis are typically about ___ high in the open ocean, and ___ high on reaching shallow water.

Answer 22

• 1 meter, 6-15 meters

Question 23

Tsunamis are created by massive jolts of energy delivered to a mass of water by all but which of the following?

Answer 23

• hurricanes

Question 24

The most common trigger for tsunamis are

Answer 24

• earthquakes

Question 25

Which of the following statements best explains how earthquakes trigger tsunamis?

Answer 25

• earthquakes shift the sea floor up or downward, causing water to be displaced

Question 26

The 2004 Indian Ocean tsunami was generated by huge earthquakes along ____ off the shore of Suntratra.

Answer 26

• subduction zone

Question 27

The Pacific Tsunami Warning Centre (PTWC) declares a “tsunami watch” when an earthquake meeting three criteria is identified. Which of the following characteristics is needed for a watch to be issued?

Answer 27

• Richter magnitude of 7.0 or greater
• hypocentre shallower than 100 kilometres
• epicenter on ocean floor

Question 28

Modern tsunami warning systems make use of ____ to issue a “tsunami warning”

Answer 28

• tidal gauges

- seafloor pressure sensors

Question 29

Japan had several countermeasures against tsunami in place prior to the 9.0 magnitude Took earthquake of 2011. Why then was the death toll so high?

Answer 29

• the tsunami run-up was underestimated in many locations therefor the countermeasures were under designed and all short of mitigating the hazard

Question 30

Before the first big wage of a tsunami, the sea may either ___ or suddenly ___.

Answer 30

• withdraw, rise

Question 31

Mass movement is the movement of earth materials downslope due to ___.

Answer 31

• gravity

Question 32

External processes that increase the odds of a slope failure include ____.

Answer 32

• removing support rom low on a slope, as by stream or ocean-wave erosion
• steepening the slope, as by fault movements
• adding mass high on a slope, as in the sediment deposition

Question 33

The materials most commonly associated with earth failure are ___.

Answer 33

• clay minerals

Question 34

Which of the following statements regarding clay minerals is true?

Answer 34

• clay minerals from these ice view are thin and flat, and they commonly form book-like structures
• clay minerals expand and contract as they absorb and lose water
• as clay minerals take in new elements and lose others, they increase and decrease in strength

Question 35

Water weakens earth materials in which ways?

Answer 35

• through interplay with clay minerals
• decreasing the cohesion of rocks
• congelifraction

Question 36

Many hill slope masses are weak due to preexisting geologic conditions such as ____.

Answer 36

• structures within the rocks, such s fractures, ancient faults, and soft rock layers

Question 37

Of the following types of mass movements, which can move fastest?

Answer 37

• avalanche

Question 38

The speed of movement varies markedly in different types of mass movements. Which of the following are in the correct sequence going from slow to rapid movement?

Answer 38

• creep, translational slide, rock fall

Question 39

the presence of talus slopes indicate that ___ have occurred in the past.

Answer 39

• rock fall

Question 40

The 1903 Frank slide is an example of ____.

Answer 40

• a debris avalanche

Question 41

Catastrophic subsidence into sinkholes occurs more often in areas that are underlain by ____.

Answer 41

• limestones

Question 42

Slab avalanches can be triggered by all but which of the following?

Answer 42

• acoustic vibrations

Question 43

Avalanche forecasting is based on ____.

Answer 43

• weather conditions
• assessment of the snow pack
• observations of recent avalanches

Question 44

Slope stability is increased by ___ and decreased by ____.

Answer 44

• supporting the base or toe of the slope; increasing slope angle.