Midterm #2 Questions Flashcards
The majority Earth’s volcanic activity occurs in which of these tectonic settings?
- spreading centres
The volcanoes of the Cascade Range, including Mr. Garibaldi in British Columbia and St. Helens in Washington, result from ____.
- the subduction of the Juan de Fuca plate beneath North America
Volcanoes in Canada result from ____.
- a hot spot
- subduction
- rifting
The more than 200 dormant valances in Canada are concentrated in ____.
- British Columbia and Yukon
Mount Garibaldi in southwest British Columbia is a ___.
- stratovolcano
Ways of generating pyroclastic flows include ___.
- 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
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 ___.
- a basaltic magma in the subsurface
Several geologic phenomenas are being studies as signs of an impending volcanic eruption. These include seismic waves, ____, and the release of gases.
- ground deformation
If a volcanologist installs a sensitive seismometer besides a volcano and it detects longer-period seismic waves this means that ____.
- magma eruption is imminent
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)
- true
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)
- False
The Indonesian word Lahar refers to the buoyant ash plume associated with Plinian type eruptions. (True or False)
- False
Haze can produce a cooling effect on Earth while excess of carbon dioxide causes warming. (True or False)
- True
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.
- False
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
- elliptical
When wind caused waves approach the shoreline, friction causes them to show their wavelengths to ___ resulting in waves ____.
- decrease, growing taller
Tsunamis typically have ___ relative to wind-blown waves.
- long periods and long wavelengths
Tsunamis wavelengths can be as great as ____.
- 800 km
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?
- the waves increase in amplitude and decrease in velocity
Tsunamis arrive as a series of several waves separated by periods typically in the ____ range.
- 10-60 minutes
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 ____.
- tsunamis are rarely felt in deep water because they have long wavelengths and low heights.
Tsunamis are typically about ___ high in the open ocean, and ___ high on reaching shallow water.
- 1 meter, 6-15 meters
Tsunamis are created by massive jolts of energy delivered to a mass of water by all but which of the following?
- hurricanes
The most common trigger for tsunamis are
- earthquakes
Which of the following statements best explains how earthquakes trigger tsunamis?
- earthquakes shift the sea floor up or downward, causing water to be displaced
The 2004 Indian Ocean tsunami was generated by huge earthquakes along ____ off the shore of Suntratra.
- subduction zone
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?
- Richter magnitude of 7.0 or greater
- hypocentre shallower than 100 kilometres
- epicenter on ocean floor
Modern tsunami warning systems make use of ____ to issue a “tsunami warning”
- tidal gauges
- seafloor pressure sensors
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?
- the tsunami run-up was underestimated in many locations therefor the countermeasures were under designed and all short of mitigating the hazard
Before the first big wage of a tsunami, the sea may either ___ or suddenly ___.
- withdraw, rise
Mass movement is the movement of earth materials downslope due to ___.
- gravity
External processes that increase the odds of a slope failure include ____.
- 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
The materials most commonly associated with earth failure are ___.
- clay minerals
Which of the following statements regarding clay minerals is true?
- 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
Water weakens earth materials in which ways?
- through interplay with clay minerals
- decreasing the cohesion of rocks
- congelifraction
Many hill slope masses are weak due to preexisting geologic conditions such as ____.
- structures within the rocks, such s fractures, ancient faults, and soft rock layers
Of the following types of mass movements, which can move fastest?
- avalanche
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?
- creep, translational slide, rock fall
the presence of talus slopes indicate that ___ have occurred in the past.
- rock fall
The 1903 Frank slide is an example of ____.
- a debris avalanche
Catastrophic subsidence into sinkholes occurs more often in areas that are underlain by ____.
- limestones
Slab avalanches can be triggered by all but which of the following?
- acoustic vibrations
Avalanche forecasting is based on ____.
- weather conditions
- assessment of the snow pack
- observations of recent avalanches
Slope stability is increased by ___ and decreased by ____.
- supporting the base or toe of the slope; increasing slope angle.
