Geol 9 Chapter 8 -Tsunami Versus Wind-Caused waves

True or false: Tsunami waves are just big wind waves.

False

True or false: People on the coast will always feel an earthquake before a tsunami hits.

False Reason: Often, the earthquake occurs far enough away that it is not felt by people who are later affected by the tsunami.

True or false: 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.

False Reason: The Japanese tsunami traveled across the Pacific, causing damage in locations as far-flung as Hawaii, California, and Chile.

This image shows that the orbital motions of water particles become more elliptical in shape as waves approach the shore. Why is this?

Friction from the shallow seafloor interferes with the orbital motion.

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?

Ghost forests of dead tree trunks in tidal marshes

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

Head for high ground. Climb to the top of a strong building. Abandon your possessions.

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?

Human population has quadrupled since 1883.

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

Indian or India

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

Indo-Australian

The 2004 Indian Ocean tsunami killed over 100,000 people in Indonesia, whereas the 2011 Japanese tsunami killed only around 19,000 people. Why is this?

Japan has a sophisticated tsunami warning system.

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

Long period Ultra-long wavelength

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

Meteorite impact Underwater landslide Volcanic eruption Fault movement

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

Must have a magnitude of at least 7.5Mw Must move the seafloor vertically up or down

Which of the following attributes can be used to distinguish between normal ocean waves (as shown here) and tsunami?

Ocean waves break at the shore and retreat. Tsunami have longer wavelengths. Ocean waves are generated by the wind.

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

Removal of offshore coral reefs Removal of coastal forests

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

Subduction zone

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

The fault movement was unusually slow, generating mostly long-period seismic waves.

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

The impact of tsunami on harbors is great because the narrowness of harbors focuses tsunami into even larger waves.

What is fetch?

The length of the water surface the wind blows across

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

The long wavelength of the tsunami allowed it to bend around the island.

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?

The maximum ocean depth is approximately 11 km.

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

The remains of plants that were buried by sands deposited on land by the tsunami

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

The sea suddenly withdraws from the shore. A large earthquake A sudden change in how the ocean water is behaving A loud siren starts blaring.

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

The wave amplitude increases. The wave velocity decreases. Water builds up behind the wave front.

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?

Their oral history instructed them to run for high ground when the ground starts shaking.

True or false: Tsunami can be generated by earthquakes that do not produce significant shaking.

True

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

True Reason: They are very fast but not very high in the open ocean.

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

Tsunami affect the entire water column and therefore drag along the ocean floor, which reduces the wave velocity.

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

Tsunami alert system Coastal barrier walls

Why is tidal wave a poor name for tsunami?

Tsunami have nothing to do with the tides.

Which of the following are examples of tsunami hazard mitigation?

Tsunami warning systems Warning signs Hazard maps

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?

Water depth

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

You probably wouldn't notice the tsunami as tsunami waves are generally only a meter in height in open water.

The 2011 Japanese tsunami was caused by ______.

a magnitude 9.0 earthquake

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

a massive earthquake off the coast of Sumatra, Indonesia

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

decrease

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

decrease; increase

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

displace large volumes of ocean water

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

downward; upward

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.

earthquake

The most common cause of tsunami is _______.

earthquakes

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 ______.

evidence of damage was washed away by the tsunami

Tsunami are commonly generated along subduction zones because ______.

fault movements at subduction zones commonly have a vertical component

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 ______.

fetch Reason: This is the length of the water surface the wind blows across.

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

friction

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

in a nearly circular orbit

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

increase, rise, or change

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

longer, larger, or bigger

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

makes tsunami risk worse

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

In open water, the orbital motion of waves ceases at a depth of approximately _______.

one-half of the wavelength

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

one-half their wavelength

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

pressure

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

raised the seafloor by tens of feet, displacing vast amounts of seawater

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

retreat of the ocean

When a tsunami comes onshore, it _______.

rushes inland like a rising tide

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

seismic waves

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

spring upward and seaward

A tsunami devastated Indonesia in 1883 when ______.

the volcano Krakatau erupted and collapsed into the sea

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

they have very long wavelengths

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

tidal wave

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

tsunami

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

tsunami

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.

tsunami

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

tsunami

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

tsunami hazard

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

tsunamis

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

vertical

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 ________.

vertical motion on the fault

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

wavelengths

Ordinary ocean waves are created by ______.

wind

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

Blank 1: velocity Blank 2: fetch

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

Blank 1: wind Blank 2: earthquakes

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

26 December 2004