Geol 9 Chapter 8 - Tsunami Waves
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Questions and Answers

The 2011 Japanese tsunami was caused by ______.

a magnitude 9.0 earthquake

Why did the 2004 Indian Ocean tsunami kill over 100,000 people in Indonesia, whereas the 2011 Japanese tsunami killed only around 19,000 people?

Japan has a sophisticated tsunami warning system.

The 2011 Japanese tsunami caused damage in other locations including ______.

massive bird deaths on Midway Atoll, damage to homes in Chile, dock and boat damage in California

Which of the following is evidence for a major earthquake in the Pacific Northwest that caused 1 to 2 meters of coastal subsidence in 1700?

<p>Ghost forests of dead tree trunks in tidal marshes</p> Signup and view all the answers

Which type of plate boundary is associated with most killer tsunamis?

<p>Subduction zone</p> Signup and view all the answers

The magnitude 9.0 earthquake that rocked Japan on 11 March 2011 generated a(n) _______ that resulted in the deaths of over 19,000 people.

<p>tsunami</p> Signup and view all the answers

Normal ocean waves are generated by the _______, whereas tsunami are mostly generated by _______.

<p>wind; earthquakes</p> Signup and view all the answers

Which of the following are kinds of tsunami preparation used in Japan?

<p>Tsunami alert system</p> Signup and view all the answers

The Japanese earthquake and tsunami caused billions of dollars of damage in Japan, but their effects weren't really felt around the rest of the world.

<p>False</p> Signup and view all the answers

How do we know the large earthquake of 1700 that occurred offshore of the Pacific Northwest generated a large tsunami?

<p>The remains of plants that were buried by sands deposited on land by the tsunami</p> Signup and view all the answers

Tsunami waves are just big wind waves.

<p>False</p> Signup and view all the answers

When wind energy is transferred to the water, waves form and particles of water move _______.

<p>in a nearly circular orbit</p> Signup and view all the answers

Ordinary ocean waves are created by ______.

<p>wind</p> Signup and view all the answers

The height of a wave depends on the ______ of the wind, the time the wind blows, the _______, and the consistency of the wind direction.

<p>velocity; fetch</p> Signup and view all the answers

What is fetch?

<p>The length of the water surface the wind blows across</p> Signup and view all the answers

Why does the name tsunami come from the Japanese terms for harbor and wave?

<p>The impact of tsunami on harbors is great because the narrowness of harbors focuses tsunami into even larger waves.</p> Signup and view all the answers

Waves are created when wind energy is transferred to the water surface through the force of ______.

<p>friction</p> Signup and view all the answers

Wave height in open, deep water is controlled by wind speed, the length of time the wind blows, the consistency of wind direction, and the ______.

<p>fetch</p> Signup and view all the answers

Waves will slow down when they reach water that is less than _________ deep.

<p>one-half their wavelength</p> Signup and view all the answers

Why is tidal wave a poor name for tsunami?

<p>Tsunami have nothing to do with the tides.</p> Signup and view all the answers

When waves slow down in shallow water, their wavelengths ______ and their wave heights ______.

<p>decrease; increase</p> Signup and view all the answers

Named for the Japanese words for harbor and wave, _______ are giant, long-period waves caused by oceanic disturbances.

<p>tsunamis</p> Signup and view all the answers

Fault movements, volcanic eruptions, underwater landslides, and meteorite impacts can all generate tsunami because they ______.

<p>displace large volumes of ocean water</p> Signup and view all the answers

The most common cause of tsunami is _______.

<p>earthquakes</p> Signup and view all the answers

Calling a tsunami a _______ _______ is inaccurate because they are not generated by tides.

<p>tidal wave</p> Signup and view all the answers

Which of the following attributes can be used to distinguish between normal ocean waves and tsunami?

<p>All of the above</p> Signup and view all the answers

Whereas the velocity of a wind-blown wave can be calculated if you know its wavelength, what piece of information do you need to know to calculate the velocity of a tsunami?

<p>Water depth</p> Signup and view all the answers

Which of the following can cause tsunami by displacing a large amount of water?

<p>Volcanic eruption</p> Signup and view all the answers

Calculated tsunami velocities are typically faster than measured tsunami velocities. Why is this?

<p>Tsunami affect the entire water column and therefore drag along the ocean floor, which reduces the wave velocity.</p> Signup and view all the answers

Tsunami are commonly generated along subduction zones because ______.

<p>fault movements at subduction zones commonly have a vertical component</p> Signup and view all the answers

Which of the following occur when a tsunami reaches the shore?

<p>All of the above</p> Signup and view all the answers

The periods and lengths of tsunami waves are much _______ than those of wind waves.

<p>longer</p> Signup and view all the answers

A tsunami passing a ship on the open ocean may go unnoticed by those on board.

<p>True</p> Signup and view all the answers

Waves disturb the water column to a depth of one-half their wavelength. Tsunami have wavelengths of up to 780 km, meaning that ocean water up to 390 km in depth will be disturbed. Why is this impossible?

<p>The maximum ocean depth is approximately 11 km.</p> Signup and view all the answers

When the trough of a tsunami reaches shore before the crest, a _________ will be observed.

<p>retreat of the ocean</p> Signup and view all the answers

When a tsunami reaches the shore, both the wavelength and velocity _______, whereas the amplitude increases.

<p>decrease</p> Signup and view all the answers

If you were on a ship in the open ocean and a tsunami passed by, what would you experience?

<p>You probably wouldn't notice the tsunami as tsunami waves are generally only a meter in height in open water.</p> Signup and view all the answers

Tsunami are able to rush inland for great distances because _______.

<p>they have very long wavelengths</p> Signup and view all the answers

When a tsunami comes onshore, it _______.

<p>rushes inland like a rising tide</p> Signup and view all the answers

When the 2004 Indian Ocean tsunami hit Sri Lanka, it affected almost the entire shoreline of the island. Why is this?

<p>The long wavelength of the tsunami allowed it to bend around the island.</p> Signup and view all the answers

Tsunami are commonly generated at subduction zones because the faults there have a strong component of ______ motion.

<p>vertical</p> Signup and view all the answers

As can be seen in this image, when a subduction zone becomes locked, the seaward edge bows _____ and the landward side bows ______.

<p>downward; upward</p> Signup and view all the answers

The Indian Ocean tsunami, which killed about 245,000 people in 14 countries, occurred on _______.

<p>26 December 2004</p> Signup and view all the answers

Which of the following attributes are responsible for the destructive power of tsunami?

<p>All of the above</p> Signup and view all the answers

The long _______ and periods of tsunami make them particularly dangerous to small islands, as the wave can pass over the entire island.

<p>wavelengths</p> Signup and view all the answers

Which of the following are requirements for an earthquake to generate a tsunami?

<p>Both A and B</p> Signup and view all the answers

When a locked subduction zone finally slips, the overriding plate will ______.

<p>spring upward and seaward</p> Signup and view all the answers

The 26 December 2004 Indian Ocean tsunami was caused by ______.

<p>a massive earthquake off the coast of Sumatra, Indonesia</p> Signup and view all the answers

The deadliest tsunami in history occurred on 26 December 2004 in the _______ Ocean.

<p>Indian</p> Signup and view all the answers

The magnitude 9.1 earthquake that struck Indonesia on 26 December 2004 must have caused extensive damage. However, the extent of damage cannot be assessed because ______.

<p>evidence of damage was washed away by the tsunami.</p> Signup and view all the answers

An enormous earthquake on 26 December, 2004, just off the coast of Sumatra, generated a(n) _______ that killed over 245,000 people.

<p>tsunami</p> Signup and view all the answers

The 2004 Indian Ocean tsunami was so powerful because the rupture that caused the earthquake ______.

<p>raised the seafloor by tens of feet, displacing vast amounts of seawater.</p> Signup and view all the answers

The death toll for the 1883 tsunami caused by the collapse of Krakatau was 36,000. The death toll for the 2004 Indian Ocean tsunami was approximately 245,000. Why was the death toll so much higher in 2004?

<p>Human population has quadrupled since 1883.</p> Signup and view all the answers

The shaking damage caused by the 26 December 2004 earthquake in Indonesia was quickly erased by the _______ that swept over the land.

<p>tsunami</p> Signup and view all the answers

If you are near the coast and feel an earthquake, you should consider the possibility of a(n) ______.

<p>tsunami</p> Signup and view all the answers

The earthquake that generated the 2004 Indian Ocean occurred due to subduction of the _______ plate.

<p>Indo-Australian</p> Signup and view all the answers

You are on a beach. Which of the following can alert you to an incoming tsunami?

<p>All of the above</p> Signup and view all the answers

A tsunami devastated Indonesia in 1883 when ______.

<p>the volcano Krakatau erupted and collapsed into the sea.</p> Signup and view all the answers

On Simuele Island, which lies very close to the epicenter of the 2004 magnitude 9.1 earthquake, only 7 of the 75,000 inhabitants were killed by the tsunami that ravaged their coastline. Why was this?

<p>Their oral history instructed them to run for high ground when the ground starts shaking.</p> Signup and view all the answers

Why didn't the coastal residents of Nicaragua feel the nearby earthquake that generated a devastating tsunami in 1992?

<p>The fault movement was unusually slow, generating mostly long-period seismic waves.</p> Signup and view all the answers

People on the coast will always feel an earthquake before a tsunami hits.

<p>False</p> Signup and view all the answers

Which of the following are ways in which human activities can increase the impact of tsunami?

<p>All of the above</p> Signup and view all the answers

Which of the following are examples of tsunami hazard mitigation?

<p>All of the above</p> Signup and view all the answers

Which of the following are actions you should take if you suspect a tsunami is coming?

<p>All of the above</p> Signup and view all the answers

Warnings about a possible tsunami that follow a major earthquake can be generated by scientists far from the epicenter by analyzing _____

<p>seismic waves</p> Signup and view all the answers

People on Simeulue Island knew to run to high ground when a very large _______ occurred in 2004 because they remembered their ancestors' stories of large waves following ground shaking.

<p>earthquake</p> Signup and view all the answers

DART II sensors can detect a tsunami by recording changes in water ______.

<p>pressure</p> Signup and view all the answers

Tsunami can be generated by earthquakes that do not produce significant shaking.

<p>True</p> Signup and view all the answers

Coral reefs and natural vegetation absorbs tsunami energy; our removing these features ______.

<p>makes tsunami risk worse</p> Signup and view all the answers

This is an example of a _______ _______ map, a useful tool in providing information to homeowners and business.

<p>tsunami hazard</p> Signup and view all the answers

Rapid analysis of seismic waves can be used to determine the magnitude, location, and depth of an earthquake. Perhaps most importantly for tsunami hazard assessment, it can be used to determine whether there was ________.

<p>vertical motion on the fault</p> Signup and view all the answers

As a tsunami wave passes over a DART II sensor, the sensor will detect a(n) _______ in water pressure.

<p>increase</p> Signup and view all the answers

Study Notes

Tsunami Overview

  • The 2011 Japanese tsunami was triggered by a magnitude 9.0 earthquake.
  • The 2004 Indian Ocean tsunami caused over 100,000 fatalities in Indonesia, whereas the 2011 Japanese event resulted in about 19,000 deaths, attributed to Japan's advanced tsunami warning system.

Impact and Evidence

  • The 2011 tsunami had far-reaching effects, such as massive bird deaths on Midway Atoll, damage to homes in Chile, and impacts to docks and boats in California.
  • Evidence of a major 1700 earthquake in the Pacific Northwest includes ghost forests of dead tree trunks found in tidal marshes.

Tsunami Characteristics

  • Killer tsunamis typically arise from subduction zones, characterized by fault movements with a vertical component.
  • Tsunami differ from normal waves, which are primarily wind-generated; tsunamis are predominantly caused by earthquakes or other significant disturbances.

Tsunami Mechanics

  • Normal ocean waves are affected by wind's velocity and fetch, while tsunami waves have much longer wavelengths and periods, increasing their destructive potential.
  • As tsunami approach shallow waters, their wavelengths decrease and heights increase, intensifying their impact inland.

Historical Context

  • The deadliest tsunami in history occurred on December 26, 2004, in the Indian Ocean, impacting 14 countries and resulting in approximately 245,000 deaths.
  • The 2004 tsunami was fueled by an earthquake that raised the seafloor, displacing vast amounts of seawater.

Tsunami Warning and Preparedness

  • Key elements of tsunami preparedness in Japan include a tsunami alert system and coastal barrier walls.
  • Signs of an impending tsunami include sudden withdrawal of the sea, strong earthquakes, and specific ocean behavior changes.

Mitigation Strategies

  • Human activities like removing coral reefs and coastal forests can enhance tsunami risk.
  • Effective tsunami hazard mitigation involves warning signs, hazard maps, and comprehensive tsunami warning systems.

Response and Safety

  • If a tsunami is suspected, individuals should seek high ground, climb strong structures, and leave belongings behind.
  • Those on ships may not notice a tsunami as it is typically only a meter high in deep water.

Technology and Tsunami Detection

  • DART II sensors detect tsunamis by measuring changes in water pressure.
  • Rapid analysis of seismic waves post-earthquake can determine the event's magnitude and identify any vertical fault motion, critical for assessing tsunami risk.

Conclusion

  • Tsunamis can occur from diverse sources, including earthquakes, volcanic eruptions, and meteorite impacts.
  • Understanding the mechanics, risks, and advancements in detection and preparedness is crucial for mitigating tsunami impacts effectively.

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Description

Explore the key concepts outlined in Chapter 8 of Geology 9 regarding tsunamis and wind-caused waves. This quiz will examine the causes and impacts of notable tsunamis, such as those in 2011 and 2004, as well as the significance of effective warning systems.

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