ISNS Ch 8

What caused the spectacular seiche event at Lake Hebgen, Montana, on 17 August 1959?

Downward motion on two normal faults that run across the northern end of the lake

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

False

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 (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. Abandon your possessions. Climb to the top of a strong building.

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

Indian

How did the 18 November 1929 earthquake cause the Newfoundland tsunami that devastated the Burin Peninsula?

It triggered a submarine landslide.

The largest historic tsunami wave run-up ever recorded (1,600 feet) occurred at ______.

Lituya Bay, Alaska

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

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

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 of the following were factors that contributed to the 18 November 1929 tsunami that affected Newfoundland, Canada?

Submarine landslide Earthquake

Lake _____, located in California and Nevada, was created by movement along parallel faults that are still active and is therefore at risk of tsunami.

Tahoe

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.

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

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.

Which of the following are the three ways in which volcanoes can cause tsunami?

They collapse. They explode. They send debris into the water.

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

True

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.

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

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

The 1964 Good Friday tsunami that raced through the entire Pacific Ocean was caused by _______.

a mega-thrust earthquake along the convergent plate boundary between the Pacific and North American plates

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

An event in which the side of a volcano breaks off, forming a large landslide, is called a(n) ____ _____.

flank OR sector collapse

Large debris avalanche deposits found on the seafloor around the Hawaiian islands have been attributed to ________.

flank collapse of the Hawaiian volcanoes

Landslides that flow into seas and lakes and create tsunami are driven by the force of _____.

gravity

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

The 1998 Papua, New Guinea, tsunami taught us that ________.

it doesn't take a large earthquake to cause a tsunami; small earthquakes can trigger submarine landslides, which in turn generate tsunami

Although it is situated far from the Pacific Ocean, Lake Tahoe is at risk from a tsunami because ________.

it is bounded by normal faults that could drop the lake bottom by 4 meters

Locally, tsunami caused by ______ can be bigger and cause larger run-ups of water than those caused by earthquakes.

landslides

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 dock and boat damage in California damage to homes in Chile

The 1 April 1946 Alaskan tsunami that destroyed the lighthouse shown here was caused by ______.

movement along a subduction zone

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

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

retreat of the ocean

The largest historic tsunami wave run-up ever recorded was caused by a massive ______ into the water following a magnitude 8 earthquake on the Fairweather fault.

rockfall OR landslide OR rockslide

When a tsunami comes onshore, it _______.

rushes inland like a rising tide

An oscillating wave that sloshes back and forth within an enclosed body of water is called a(n) _______.

seiche

The event that sent water flowing back and forth across Lake Hebgen in Montana for over 11 hours was a spectacular example of a(n) ________.

seiche

The lowering of coastal lands due to the 2011 Japanese earthquake is called _______.

subsidence (This subsidence allowed the tsunami to run farther up on land than expected.)

A set of waves created by a storm is a sea

swell

An ocean ______ is a series of regular, long-period waves that are formed through the interference of multiple sets of ocean waves.

swell

The cataclysmic eruption of Krakatau on 27 August 1883 generated a tsunami through ________.

the collapse of the volcano into the sea

One of the reasons that the tsunami overran many coastal barriers in Japan is that _______.

the earthquake caused the coastal land to move downward, lowering the barriers

An important feature of the 1964 Good Friday earthquake that led to the generation of such a large tsunami was _______.

the massive vertical and horizontal motion of the plate overlying the subducting Pacific plate

Many of those killed in Hawaii by the 1 April 1946 Alaskan tsunami died because ______.

they thought the tsunami warnings were an April Fool's Day joke

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

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

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

tsunamis

Match the equation to calculate wave velocity to the correct type of wave.

v = 1.25√L --> wind wave v= √gD --> tsunami wave

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

vertical

By exploding, collapsing, and sending debris into the water, _____ can create tsunamis.

volcanoes

The 22 May 1960 earthquake in Chile ______.

was the largest ever recorded generated deadly tsunami

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

wind earthquakes

The most powerful earthquake ever measured occurred in ______ on 22 May 1960.

Chile

What is a seiche?

An wave that sloshes back and forth within an enclosed body of water

The 1883 tsunami caused by the eruption of Krakatua was the most deadly in history until the ______.

2004 Indian Ocean tsunami

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

26 December 2004

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

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

Approximately 2,200 people were killed in July 1998, when a tsunami struck Papua, New Guinea. What generated this tsunami?

A submarine landslide that was triggered by a magnitude 7.1 earthquake