Deck 6: Earthquakes and Volcanoes

Question 1

Describe what tectonic settings determine the nature of a volcanic eruption? How do these factors affect a magmas viscosity?

Answer 1

The tectonic settings that determine the nature of a volcanic eruption include the type of plate boundary, the composition of the magma, and the amount of water and gas dissolved in the magma.

At convergent plate boundaries, where one tectonic plate is forced beneath another, the resulting volcanic eruptions are often explosive due to the high viscosity of the magma. This is because the subduction of oceanic crust introduces water and other volatiles into the mantle, which leads to the formation of viscous and gas-rich magma. This type of magma tends to trap gas bubbles, leading to explosive eruptions.

On the other hand, at divergent plate boundaries, where tectonic plates move apart, the volcanic eruptions are often less explosive and are characterized by the eruption of basaltic lava. This is because the magma formed at divergent boundaries is typically less viscous and contains fewer dissolved gases, allowing for the relatively smooth flow of lava.

The factors that affect a magma's viscosity include its temperature, composition, and the amount of dissolved gases. Generally, higher temperatures and lower silica content lead to lower viscosity, while higher silica content and the presence of dissolved gases lead to higher viscosity.

In summary, tectonic settings play a crucial role in determining the nature of volcanic eruptions by influencing the composition and viscosity of the magma. This, in turn, affects the explosiveness and behavior of the eruptions.

Question 2

Describe in detail how scientists can determine the location of an earthquake epicenter.

Answer 2

Scientists can determine the location of an earthquake epicenter using a method called triangulation. This process involves using data from three or more seismograph stations to pinpoint the exact location of the earthquake.

First, when an earthquake occurs, it releases energy in the form of seismic waves. These waves travel through the Earth and are recorded by seismograph stations located around the world. Each station records the arrival time of the seismic waves, which provides valuable information for determining the epicenter.

To begin the triangulation process, scientists first measure the time it takes for the seismic waves to reach each seismograph station. By comparing the arrival times of the waves at different stations, scientists can calculate the distance the waves traveled from the epicenter to each station.

Next, scientists draw circles on a map around each seismograph station, with the radius of each circle representing the distance the seismic waves traveled to reach that station. The intersection of these circles is the estimated location of the earthquake epicenter.

By using data from at least three seismograph stations, scientists can accurately determine the location of the earthquake epicenter. This information is crucial for understanding the impact of the earthquake and for providing early warnings to areas at risk of aftershocks or tsunamis.

Question 3

When slippage of rock occurs along a break or fracture in a rock, the fracture is called a __________ .

Answer 3

fault

Question 4

The __________ hypothesis suggests that some fault surfaces are rough so that the rock masses on either side of the fault become locked against one another rather than slipping easily past.

Question 5

When an earthquake occurs, the elastically stored energy is carried outward from the focus to other parts of Earth by vibrations called __________ .

Question 6

__________ are seismic waves that pass through a rock mass by elastically deforming the rock.

Question 7

__________ travel around Earth rather than through it.

Question 8

The point where energy is first released during an earthquake is called the __________ .

Question 9

Very large earthquakes are relatively __________ .

Question 10

__________ magnitude is calculated from the maximum recorded amplitudes of seismic waves with a correction for distance from the epicenter.

Question 11

The sudden disturbance of water-saturated sediment and soil can turn solid ground to a liquid-like mass. This process is called _________ .

Question 12

__________ occurs when the speed of a wave changes as it passes from one medium to another, causing the wave path to bend.

Question 13

__________ waves are reflected and refracted as they travel through the planet and encounter materials with different physical properties.

Question 14

The deepest and most powerful earthquakes occur in the __________ tectonic environment.

Question 15

__________ is a mixture of molten rock, suspended mineral grains, and dissolved gases.

Question 16

__________ magma contains about 50% silicon dioxide and little dissolved gas.

Question 17

Viscous magmas have __________ silica content than less viscous magmas and have __________ dissolved-gas content.

Question 18

__________ are steep conical mountains that consist of layers of both lava and tephra.

Question 19

A common sign of an imminent volcanic eruption includes swarms of small __________ of increasing frequency or intensity.

Question 20

The ring of andesitic volcanoes surrounding the Pacific Rim is called the __________.

Question 21

Earthquakes occur when rock masses break and slip past one another along a fault.

Question 22

Surface waves travel through Earth rather than around it.

Question 23

The focus is the point on a fault where energy is first released during an earthquake.

Question 24

Large-magnitude earthquakes are quite frequent.

Question 25

Most seismic activity takes place along passive tectonic plate boundaries.

Question 26

Along the Ring of Fire, volcanoes can occur, but not earthquakes.

Question 27

The higher the density of material, the faster seismic body waves travel through it.

Question 28

The deepest and most powerful earthquakes occur in subduction zone environments.

Question 29

Subduction zones tend to have only deep-seated (rather than shallow) earthquakes.

Question 30

A volcano is a vent from which lava, pyroclasts, or gases are erupted.

Question 31

The higher the temperature of the magma, the lower its viscosity.

Question 32

Partial melting occurs when part of a rock melts and part remains solid.

Question 33

Magma is more dense than solid rock and therefore rises against the weight of the overlying rock.

Question 34

Viscous andesitic and rhyolitic magma have higher silica and dissolved-gas contents, and erupt at lower temperatures than basaltic magma.

Question 35

The shape of a volcano is determined by the kind of magma it erupts and the relative proportions of lava and pyroclasts.

Question 36

There are about 10,000 active volcanoes today, many of them in the circum-Pacific region.

Question 37

Volcanism provides nuclear energy and plays an important role in the formation of some mineral deposits.

Question 38

Plutons are bodies of magma that reach the surface.

Question 39

Igneous rocks that cool and solidify at or near the surface are plutonic rocks.

Question 40

What does the Richter magnitude scale measure?

A) The number of tsunami as a result of an earthquake.
B) The reaction of people during an earthquake.
C) The amount of damage encountered during an earthquake.
D) The magnitude of the Earth shaking during an earthquake.

Question 41

What type of volcano is a result of thick, viscous magma (rather than fluid magma)?

A) Shield volcano
B) Stratovolcano
C) Both of these.
D) Neither of these.

Question 42

What is one of the reasons why scientists believe the outer core is liquid?

A) P-wave shadow zone.
B) S-wave shadow zone.
C) Outer core fish fossils that have made their way to the surface.
D) Negative gravity anomalies.

Question 43

Why have no earthquakes greater than a magnitude of around 10 ever been observed?

A) We just haven't observed it yet, but it can definitely happen.
B) Rocks only have enough strength to store a finite amount of elastic energy before they reach the breaking point.
C) The seismograph is not equipped to measure amplitude at that level.
D) None of these.

Question 44

What is the minimum number of location data points needed in order to determine the location of the epicenter of an earthquake?

A) Five.
B) Four.
C) Three.
D) Two.

Question 45

If you're a ship in the middle of the sea, can you feel a tsunami when it passes underneath you?

Question 46

Let's assume an earthquake occurs somewhere along the San Andreas fault. A seismograph based in Los Angeles, California monitors the earthquake. In which order will the seismic waves reach the seismograph?

A) S-wave followed by P-wave followed by Surface waves.
B) P-wave followed by S-wave followed by Surface waves.
C) Surface waves followed by P-waves followed by S-waves.
D) Surface waves followed by S-waves followed by P-waves.

Question 47

The distance to an earthquake epicenter can be determined by measuring

A) The time difference of arrival of the first P-wave to S-wave.
B) The time difference of arrival of the first P-wave to Surface wave.
C) The time difference of arrival of the first S-wave to Surface wave.
D) Can't be determined.

Question 48

Seismic waves travel faster through

A) More dense material.
B) Less dense material.

Question 49

What is the major ingredient in a magma that determines whether it has high or low viscosity?

A) Carbon.
B) Iron.
C) Water.
D) Silica.

Question 50

The majority of stratovolcanoes are

A) Rhyolitic.
B) Basaltic.
C) Andesitic.

Question 51

Other than water vapor, the most abundant gas in a volcano is

A) Oxygen.
B) Sulfur dioxide.
C) Hydrogen sulfide.
D) Carbon dioxide.

Question 52

The majority of shield volcanoes are

A) Andesitic.
B) Basaltic.
C) Rhyolitic.

Question 53

A heavy cloud of hot gas and pyroclastic material which flows down the side of a volcano is called a

A) Cumulus cloud.
B) Nuée ardente.
C) Strato cloud.
D) Gaseous lava flow.

Question 54

When molten rock reaches the surface, it's called

A) Magma.
B) Lava.
C) Hot rock.
D) Plutonic rock.

Question 55

The type of igneous rock that is a result of solidification of lava is

A) Extrusive igneous rock.
B) Intrusive igneous rock.

Question 56

The area where we find the most active volcanoes are along the

A) Atlantic Basin.
B) Pacific Rim.
C) Indian Ocean Rim.
D) Along the Mediterranean Sea.

Question 57

Mount Vesuvius is an example of what type of volcano?

A) Stratovolcano.
B) Shield Volcano.
C) Cinder cone volcano.
D) None of these.

Question 58

Mount Saint Helens is an example of what type of volcano?

A) Flood basalt.
B) Shield Volcano.
C) Cinder cone volcano.
D) Stratovolcano.

Question 59

Which magma type has the highest viscosity?

A) Andesitic.
B) Basaltic.
C) Rhyolitic.

Question 60

Which type of lava flow has a smooth, ropy-looking texture?

A) Aa.
B) Pahoehoe.

Question 61

Which of the following determines whether a volcanic eruption is violent or more passive?

A) Composition of the magma.
B) Amount of dissolved gas in the magma.
C) Temperature of the magma.
D) All of these.

Question 62

Which of the following best describes Shiprock in New Mexico?

A) A recently active cinder cone volcano.
B) Exposed remains of a volcanic conduit.
C) An extinct shield volcano similar to Mauna Loa in Hawaii.
D) An extinct stratovolcano.

Question 63

Approximately how fast can a tsunami in the open ocean travel?

A) Up to 800 km/hour.
B) Up to 400 km/hour.
C) Up to 100 km/hour.
D) Up to 950 km/hour.

Question 64

Of the following states, which is most prone to earthquakes?

A) Florida.
B) Kansas.
C) California.
D) Maine.

Question 65

What are primary effects of earthquake damage (those that cause direct damage to buildings, infrastructure, and the landscape)?

A) Fires and tsunami.
B) Ground motion and landslides.
C) Surface rupture and liquefaction.
D) Ground motion and surface rupture.

Question 66

Hundreds of thousands of earthquakes occur every year. Fortunately, only one or two are large enough and close enough to major population centers to cause loss of life. During the past 800 years, there have been a handful of earthquakes that have resulted in greater than 50,000 deaths. The earthquake that resulted in the greatest number of deaths was in Shaanxi, China in 1556. It is estimated that 830,000 people lost their lives! What type of plate boundary caused such a devastating earthquake?

A) Divergent boundary.
B) Subduction zone boundary.
C) Continental collision boundary.
D) Transform fault boundary.

Question 67

What are seismic discontinuities?

A) Boundaries where the velocity of seismic waves changes smoothly rather than suddenly.
B) Boundaries where the velocity of seismic waves changes suddenly rather than smoothly.
C) Boundaries where the velocity of seismic waves increases then decreases rapidly.
D) Boundaries where the velocity of seismic waves decreases then increases rapidly.

Question 68

Assume there a magnitude 5 earthquake occurs (Richter scale magnitude). How much more energy will be released by a magnitude 8 earthquake?

A) 10 x 32 x 10 times more energy release.
B) 10 x 10 x 10 times more energy release.
C) 32 x 10 x 32 times more energy release.
D) 32 x 32 x 32 times more energy release.

Question 69

What variable(s) is(are) associated with long-term earthquake forecasting?

A) Identifying seismic gaps.
B) Understanding tectonic environments.
C) Determining patterns in recurrence intervals.
D) All of these.

Question 70

What variable(s) is(are) associated with short-term earthquake prediction?

A) Understanding tectonic environments.
B) Shorter-term prediction and early warning are nearly impossible.
C) Determining patterns in recurrence intervals.
D) Identifying seismic gaps.

Question 71

Along what type of plate boundary will shallow-focus earthquakes be the general type of earthquake (i.e., rarely, will a deep-focus earthquake occur here)?

A) Divergent boundary
B) Continental collision boundary.
C) Subduction zone boundary.
D) None of these.

Question 72

At atmospheric pressure (sea level) rocks begin to melt when heated to approximately what temperatures?

A) 100 to 200 degrees Centigrade.
B) 500 to 700 degrees Centigrade.
C) 300 to 400 degrees Centigrade.
D) 800 to 1000 degrees Centigrade.

Question 73

Where would basaltic pillow lavas generally accumulate?

A) Ocean-continental subduction zones.
B) Ocean-ocean subduction zones.
C) Mid-ocean ridges (oceanic divergent zones).
D) Continental rifts (continental divergent zones).

Question 74

What type of magma is found at Yellowstone National Park?

A) Rhyolitic.
B) Andesitic.
C) Basaltic.