Earth Science Quiz: Tsunamis

What this quiz covers

This quiz focuses on Tsunamis, giving you a quick way to practice the rules, question types, and explanations that matter most for Earth Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. The risk is low because the fault has not been active in recorded history and is therefore likely becoming dormant.
2. The risk is high; the fault type is tsunamigenic and the recurrence interval suggests significant elastic strain has accumulated. (correct answer)
3. The risk cannot be determined without knowing the exact magnitude of past earthquakes on the fault.
4. The risk is moderate because thrust faults release energy slowly, resulting in less powerful tsunamis.

Explanation: This scenario combines several key indicators of high tsunami risk. First, the fault is a shallow-angle thrust fault, the primary type that generates large tsunamis. Second, there is evidence of regular, large slip events (a recurrence interval). Third, the time since the last event is very close to the average recurrence interval, implying that the fault may be late in its seismic cycle and has accumulated significant strain, making a future large earthquake plausible. This combination points to a high-risk situation.

Question 2

1. Its extremely high wave amplitude which carries more momentum than smaller waves.
2. Its high speed, which is faster than the rate of energy dissipation due to viscous forces in the water.
3. Its extremely long wavelength, which means its energy extends through the entire water column and experiences little frictional loss at the deep seafloor. (correct answer)
4. Its formation in warm equatorial waters, which are less dense and allow for more efficient energy propagation.

Explanation: The key to a tsunami's ability to travel vast distances is its incredibly long wavelength (often hundreds of kilometers) in the deep ocean. A wave's energy is only significantly affected by friction with the seabed when the water depth is less than about half its wavelength. Because a tsunami's wavelength is so much greater than the ocean depth, it effectively does not 'feel' the bottom and thus loses very little energy to friction as it propagates, allowing it to traverse entire oceans.

Question 3

1. They amplify the wave's height by forcing it to shoal more rapidly than a sandy bottom would.
2. They have no significant effect because the tsunami's wavelength is too long to interact with the reef structure.
3. They increase the wave's speed by providing a smoother surface for it to travel over.
4. They can dissipate a significant amount of the wave's energy through friction and breaking, reducing its impact on the coast. (correct answer)

Explanation: Healthy, extensive coastal ecosystems like coral reefs and mangrove forests can act as natural barriers that mitigate tsunami impact. The complex, rough structure of a reef increases friction, forcing the wave to break and dissipating a substantial portion of its energy before it reaches the coastline. This can lead to lower wave heights, reduced inundation distances, and slower floodwater velocities, thus reducing the overall coastal risk. While a powerful tsunami will still overtop and damage the reef, its protective effect can be significant.

Question 4

1. The volcano-generated tsunami would have a much longer wavelength, allowing it to travel across oceans with less energy loss.
2. The earthquake-generated tsunami would have a higher initial wave height at the source but would dissipate more quickly.
3. The volcano-generated tsunami's energy would be more concentrated, creating extreme local run-up but less of a trans-oceanic threat.
4. The earthquake-generated tsunami would propagate from a long, linear source, while the volcano collapse would act as a point source. (correct answer)

Explanation: A large subduction zone earthquake generates a tsunami along the entire length of the fault rupture, which can be hundreds of kilometers long. This creates a linear source that directs energy efficiently across an ocean basin. A volcanic collapse, while displacing a massive volume of water, does so from a much more localized or 'point' source. This causes the wave energy to spread out radially and decrease in intensity with distance more rapidly than from a line source. While both can be devastating, this difference in source geometry is fundamental.

Question 5

1. A wave speed greater than 720 km/h and an amplitude significantly less than 0.8 meters due to energy dispersion.
2. A wave speed significantly less than 720 km/h and an amplitude significantly greater than 0.8 meters due to shoaling. (correct answer)
3. A wave speed of approximately 720 km/h and an amplitude significantly greater than 0.8 meters as the wave front steepens.
4. A wave speed significantly less than 720 km/h and an amplitude of approximately 0.8 meters as energy is lost to friction.

Explanation: As a tsunami enters shallower water, its propagation speed, which is proportional to the square root of water depth, decreases significantly. To conserve energy, the wave's kinetic energy (from its speed) is converted into potential energy, which results in a dramatic increase in its amplitude (height). This process is known as shoaling. Therefore, the wave's speed will decrease and its amplitude will increase.

Question 6

1. The earthquake's focus was exceptionally deep, indicating a massive release of energy that would disturb the entire water column.
2. The fault rupture occurred along a transform boundary, indicating powerful horizontal shearing motion.
3. The focal mechanism solution indicated predominantly vertical motion on a shallow-angle thrust fault. (correct answer)
4. Aftershock patterns revealed a very long rupture length, exceeding 500 km along the tectonic plate boundary.

Explanation: The primary mechanism for tsunami generation by an earthquake is the large-scale vertical displacement of the seafloor. A shallow-angle thrust fault, characteristic of subduction zones, produces exactly this kind of upward motion over a large area, efficiently lifting the water column above it. A deep focus (A) is less likely to cause significant seafloor deformation. Horizontal motion (B) displaces water sideways but not vertically, making it inefficient at generating tsunamis. A long rupture (D) is a factor in the tsunami's size, but the type of motion (vertical) is the essential prerequisite for generation.

Question 7

1. Tsunami waves are a form of tidal wave, and their size is governed by the local tidal cycle which peaked with the second wave.
2. The initial earthquake magnitude is often underestimated, with later seismic aftershocks increasing the tsunami's power.
3. A tsunami consists of a series of waves, known as a wave train, and the first wave is not necessarily the largest. (correct answer)
4. The withdrawal of the sea before the first wave (the trough) removes coastal water, which then returns with the larger second wave.

Explanation: A common and dangerous misconception is that a tsunami is a single event. In reality, it is a series of waves, or a 'wave train'. The first wave to arrive may be relatively small, leading to a false sense of security. Subsequent waves, arriving minutes to hours later, can be significantly larger and more destructive. Choice A is incorrect as tsunamis are unrelated to tides. Choice B is incorrect because the tsunami is generated by the main shock, not aftershocks. Choice D describes a possible precursor but doesn't explain why a later wave would be larger than the first.

Question 8

1. The epicenter only marks the starting point of the rupture, which then propagates for a great distance along the fault plane, displacing the entire seafloor above it. (correct answer)
2. The initial seismic waves radiate from the epicenter, causing the seafloor to resonate and generate secondary water waves along the trench axis.
3. The tsunami waves travel much slower than seismic waves, creating the illusion of a larger source area by the time they are detected by buoys.
4. The epicenter is the point of maximum energy release, which pushes water away in a circular pattern that is distorted into a linear shape by the trench.

Explanation: This question tests the distinction between an earthquake's epicenter and its rupture area. The epicenter is the point on the Earth's surface directly above where the earthquake rupture begins (the hypocenter). In a large megathrust event, this rupture then 'un-zips' along the fault plane for hundreds of kilometers. The entire overlying block of seafloor is what uplifts or subsides, displacing the water column. Thus, the tsunami's source is not a point (the epicenter) but a large rectangular area corresponding to the fault rupture.

Question 9

1. This indicates the arrival of the tsunami's trough, and a destructive crest is likely to follow within minutes, requiring immediate evacuation. (correct answer)
2. This is a phenomenon known as a 'minus tide' caused by the earthquake's seismic waves, which is not directly related to a subsequent tsunami wave.
3. This signals that the tsunami-generating event was a submarine landslide, which typically pulls water downward before pushing it upward.
4. The earthquake has permanently uplifted the offshore seafloor, causing a permanent and stable drop in the local sea level.

Explanation: The rapid withdrawal of the sea is a classic and extremely dangerous precursor to a tsunami. It signifies that the trough (the lowest point) of the tsunami wave has arrived first. The corresponding crest (the highest point), which carries the destructive energy, is typically only minutes behind. This is one of the most important natural warning signs, and the correct response is to evacuate to high ground immediately.

Question 10

1. Seismic data cannot accurately determine the earthquake's location, whereas DART buoys can pinpoint the tsunami's origin.
2. Not all large submarine earthquakes with vertical displacement efficiently transfer energy to the water to create a significant tsunami. (correct answer)
3. DART buoys are necessary to measure the earthquake's magnitude, which cannot be determined from land-based seismometers.
4. Seismic waves travel too slowly, so DART buoys provide a much earlier warning than seismometers can.

Explanation: Seismometers can quickly detect an earthquake, determine its location, magnitude, and focal mechanism (e.g., vertical motion). This allows scientists to identify an earthquake as potentially tsunamigenic. However, the actual generation of a tsunami depends on the complex details of the seafloor rupture and how efficiently its energy is coupled to the water column. A DART buoy provides direct confirmation by measuring the passage of the actual tsunami wave in the deep ocean. This confirmation is crucial to avoid false alarms and to verify the threat level.

Question 11

1. Wave refraction, which bent the tsunami waves toward the bay due to shallower water at the bay's entrance.
2. The Bernoulli principle, which requires the wave to speed up and decrease in height as it enters the constricted bay.
3. Topographic amplification, where the funnel-like shape of the bay constricts the wave's energy into a smaller area, increasing its height. (correct answer)
4. Sediment liquefaction within the bay, which caused the ground to subside and allowed for greater inundation.

Explanation: Coastal geography plays a critical role in tsunami risk. Bays, inlets, and harbors, particularly those that are V-shaped or funnel-like, can dramatically amplify the height of an incoming tsunami. As the wave enters the narrowing and shallowing bay, its energy is squeezed into a progressively smaller volume of water, forcing the wave amplitude (height) to increase significantly. This is a form of topographic or bathymetric amplification.

Question 12

1. The contamination of drinking water sources and agricultural land by saltwater, sewage, and hazardous materials. (correct answer)
2. The risk of another, larger tsunami wave arriving as part of the same wave train hours later.
3. The potential for powerful seismic aftershocks to cause further ground shaking in the affected area.
4. The liquefaction of water-saturated soils leading to the delayed collapse of weakened structures.

Explanation: When analyzing tsunami hazards, you need to distinguish between primary effects (the immediate physical impact of the waves) and secondary effects (the ongoing dangers that persist after the water recedes). This question tests your understanding of how natural disasters create cascading problems that extend far beyond the initial event. The correct answer is A because contamination represents a classic secondary hazard. When tsunami waters surge inland, they pick up sewage from damaged treatment facilities, saltwater that kills crops and contaminates freshwater supplies, industrial chemicals, fuel from vehicles and storage tanks, and debris containing toxic materials. This contaminated mixture then soaks into soil and groundwater systems. Even after floodwaters drain away, this contamination remains, creating serious public health risks including waterborne diseases, poisoned food supplies, and long-term environmental damage that can persist for months or years. Option B describes another wave in the same tsunami event, which is still part of the primary hazard, not a secondary effect. Option C refers to seismic aftershocks, which are related to the original earthquake that caused the tsunami, not a result of the coastal flooding itself. Option D mentions liquefaction, but this typically occurs during the earthquake phase due to seismic shaking, not as a consequence of the tsunami inundation. Remember that secondary hazards are the "disaster after the disaster." On earth science exams, look for effects that result from the primary event but create new, different types of problems that outlast the original phenomenon.

Question 13

1. The sudden impact of a large mass of rock into a confined body of water generated a wave with immense initial amplitude that could not propagate far. (correct answer)
2. The rockslide occurred during a particularly high tide, which amplified the initial wave to a great height.
3. The rockslide displaced a small volume of water, but the narrow fjord focused this energy to an extreme height.
4. The rockslide was caused by an earthquake, and the ground shaking was the primary cause of the high run-up, not the wave itself.

Explanation: When you encounter tsunami questions, focus on the relationship between the generation mechanism, the local environment, and how wave energy behaves in different settings. The 1958 Lituya Bay tsunami demonstrates how landslide-generated tsunamis differ from earthquake-generated ones. When the massive rockslide hit the water, it instantly displaced an enormous volume, creating a wave with exceptional initial amplitude. However, this type of tsunami has limited propagation ability because the energy is concentrated in the initial impact zone rather than being transmitted efficiently across ocean basins like earthquake tsunamis. The confined fjord setting meant this immense energy had nowhere to spread laterally, resulting in the record-breaking 524-meter run-up height but remaining geographically constrained. Option B incorrectly suggests tidal amplification was the primary factor, but the rockslide's massive displacement dwarfed any tidal influence. Option C gets the mechanism backwards—the rockslide actually displaced a huge volume of water, not a small one, and while the narrow fjord did contribute to focusing energy, the primary factor was the enormous initial displacement. Option D misidentifies the generation mechanism entirely; while an earthquake may have triggered the rockslide, the tsunami's extreme height resulted from the direct water displacement by falling rock, not ground shaking. Remember that landslide tsunamis typically create localized but extremely dangerous waves because they generate maximum energy at the source but don't efficiently transmit that energy over long distances like seismic sea waves do.

Question 14

1. The initial wave amplitude, which is proportional to the area of the rupture.
2. The initial wave period, which is the time elapsed between the start and end of the rupture.
3. The initial wave speed, which is calculated from the energy released over the rupture area.
4. The initial wavelength, which is fundamentally controlled by the dimensions of the displaced block of seafloor. (correct answer)

Explanation: The physical size of the source of displacement on the seafloor is the primary factor that determines the initial wavelength of the tsunami. A larger block of uplifted seafloor will create a wave with a longer wavelength. While the amount of vertical slip over this area determines the initial amplitude (A), and the speed (C) is determined by water depth, the length and width of the rupture area directly constrain the initial wavelengths of the waves that propagate away from the source.

Question 15

1. Strike-slip faults are typically located farther from coastlines, allowing any generated wave to dissipate before making landfall.
2. The energy from a strike-slip earthquake is released more slowly, resulting in a less abrupt displacement of the water column.
3. Strike-slip faulting involves predominantly horizontal motion of the seafloor, which does not efficiently displace large volumes of water vertically. (correct answer)
4. The seismic waves from strike-slip earthquakes have a different frequency that does not couple effectively with the overlying water column.

Explanation: Tsunami generation is overwhelmingly dependent on the vertical displacement of a large volume of water. Subduction zone thrust faults produce this via dip-slip motion (one plate moving up and over another). Strike-slip faults, like the San Andreas Fault, involve two plates sliding horizontally past each other. This horizontal motion is very inefficient at lifting or lowering the overlying water column, and thus even very large strike-slip earthquakes typically generate only small, localized tsunamis, if any.

Question 16

1. The earthquake's magnitude must be greater than M9.0.
2. The earthquake must involve significant vertical displacement of the seafloor. (correct answer)
3. The water depth above the fault rupture must be less than 500 meters.
4. The epicenter must be located less than 50 km from a coastline.

Explanation: Vertical displacement (dip-slip faulting) is absolutely necessary to generate a tsunami; horizontal (strike-slip) motion is ineffective. However, this condition is not sufficient by itself. A small M6.0 earthquake might occur on a thrust fault, causing some vertical displacement, but it would not displace enough water to create a powerful tsunami. To be sufficient, the vertical displacement must be large in both offset and area, which requires a high-magnitude earthquake (typically M7.5+). Therefore, vertical displacement is necessary but not sufficient.

Question 17

1. Wave refraction, which bent the tsunami waves toward the bay due to shallower water at the bay's entrance.
2. The Bernoulli principle, which requires the wave to speed up and decrease in height as it enters the constricted bay.
3. Topographic amplification, where the funnel-like shape of the bay constricts the wave's energy into a smaller area, increasing its height. (correct answer)
4. Sediment liquefaction within the bay, which caused the ground to subside and allowed for greater inundation.

Explanation: Coastal geography plays a critical role in tsunami risk. Bays, inlets, and harbors, particularly those that are V-shaped or funnel-like, can dramatically amplify the height of an incoming tsunami. As the wave enters the narrowing and shallowing bay, its energy is squeezed into a progressively smaller volume of water, forcing the wave amplitude (height) to increase significantly. This is a form of topographic or bathymetric amplification.

Question 18

1. The contamination of drinking water sources and agricultural land by saltwater, sewage, and hazardous materials. (correct answer)
2. The risk of another, larger tsunami wave arriving as part of the same wave train hours later.
3. The potential for powerful seismic aftershocks to cause further ground shaking in the affected area.
4. The liquefaction of water-saturated soils leading to the delayed collapse of weakened structures.

Explanation: When analyzing tsunami hazards, you need to distinguish between primary effects (the immediate physical impact of the waves) and secondary effects (the ongoing dangers that persist after the water recedes). This question tests your understanding of how natural disasters create cascading problems that extend far beyond the initial event. The correct answer is A because contamination represents a classic secondary hazard. When tsunami waters surge inland, they pick up sewage from damaged treatment facilities, saltwater that kills crops and contaminates freshwater supplies, industrial chemicals, fuel from vehicles and storage tanks, and debris containing toxic materials. This contaminated mixture then soaks into soil and groundwater systems. Even after floodwaters drain away, this contamination remains, creating serious public health risks including waterborne diseases, poisoned food supplies, and long-term environmental damage that can persist for months or years. Option B describes another wave in the same tsunami event, which is still part of the primary hazard, not a secondary effect. Option C refers to seismic aftershocks, which are related to the original earthquake that caused the tsunami, not a result of the coastal flooding itself. Option D mentions liquefaction, but this typically occurs during the earthquake phase due to seismic shaking, not as a consequence of the tsunami inundation. Remember that secondary hazards are the "disaster after the disaster." On earth science exams, look for effects that result from the primary event but create new, different types of problems that outlast the original phenomenon.

Question 19

1. The sudden impact of a large mass of rock into a confined body of water generated a wave with immense initial amplitude that could not propagate far. (correct answer)
2. The rockslide occurred during a particularly high tide, which amplified the initial wave to a great height.
3. The rockslide displaced a small volume of water, but the narrow fjord focused this energy to an extreme height.
4. The rockslide was caused by an earthquake, and the ground shaking was the primary cause of the high run-up, not the wave itself.

Explanation: When you encounter tsunami questions, focus on the relationship between the generation mechanism, the local environment, and how wave energy behaves in different settings. The 1958 Lituya Bay tsunami demonstrates how landslide-generated tsunamis differ from earthquake-generated ones. When the massive rockslide hit the water, it instantly displaced an enormous volume, creating a wave with exceptional initial amplitude. However, this type of tsunami has limited propagation ability because the energy is concentrated in the initial impact zone rather than being transmitted efficiently across ocean basins like earthquake tsunamis. The confined fjord setting meant this immense energy had nowhere to spread laterally, resulting in the record-breaking 524-meter run-up height but remaining geographically constrained. Option B incorrectly suggests tidal amplification was the primary factor, but the rockslide's massive displacement dwarfed any tidal influence. Option C gets the mechanism backwards—the rockslide actually displaced a huge volume of water, not a small one, and while the narrow fjord did contribute to focusing energy, the primary factor was the enormous initial displacement. Option D misidentifies the generation mechanism entirely; while an earthquake may have triggered the rockslide, the tsunami's extreme height resulted from the direct water displacement by falling rock, not ground shaking. Remember that landslide tsunamis typically create localized but extremely dangerous waves because they generate maximum energy at the source but don't efficiently transmit that energy over long distances like seismic sea waves do.

Question 20

1. Its extremely high wave amplitude which carries more momentum than smaller waves.
2. Its high speed, which is faster than the rate of energy dissipation due to viscous forces in the water.
3. Its extremely long wavelength, which means its energy extends through the entire water column and experiences little frictional loss at the deep seafloor. (correct answer)
4. Its formation in warm equatorial waters, which are less dense and allow for more efficient energy propagation.

Explanation: The key to a tsunami's ability to travel vast distances is its incredibly long wavelength (often hundreds of kilometers) in the deep ocean. A wave's energy is only significantly affected by friction with the seabed when the water depth is less than about half its wavelength. Because a tsunami's wavelength is so much greater than the ocean depth, it effectively does not 'feel' the bottom and thus loses very little energy to friction as it propagates, allowing it to traverse entire oceans.