CH. 5 Tsunami Homework Part A

True or False A tsunami is a large ocean wave that is most commonly produced when a large earthquake rupture is oceanic crustal rock pushes seawater upwards or downwards.

True

True or False Before a tsunami arrives, sea level often drops exposing the seafloor.

True

True or False Buoys in the open ocean can detect the passage of a tsunami.

True

True or False Coastlines that are far from subduction zones have a lower risk for tsunamis compared to coastlines that are near to subduction zones.

True

True or False It is possible to examine the geologic record for ancient tsunamis that were not recorded by humans.

True

True or False Tsunamis can result in fires and polluted water supplies after they strike an area.

True

True or False Tsunamis have enough erosional power to alter the landscape of coastlines that they hit.

True

True or False. Tsunamis can be caused by triggers other than earthquakes.

True

Why do ships at sea tend not to notice tsunamis?

Tsunamis in deep water have small wave height and long wavelength.

What happens to tsunami waves as they move closer to shore?

Velocity decreases and height increases.

Ocean Village wants to put in evacuation route signs. Which directions should the signs direct the villagers to go during a tsunami in order to get people to safety the fastest?

West

Which of the following locations on the Circum-Pacific Belt are likely to generate a tsunami?

West coast of South America.

A ________ is located at a plate boundary between a subducting slab of oceanic crust and an overlying plate.

Megathrust fault.

Imagine an earthquake is about to occur at location 2 on the map (Southern Alaska). Which of the following statements is most accurate?

*All locations (except 9) could benefit from an alert that an earthquake occurred at location 2, because they are near the ocean and might experience a resultant tsunami. *Most of the people living at location 2 are probably aware that they live in a location where earthquakes are likely.

1. Approximate speed of the tsunami in MPH 2. The approximate miles this tsunami traveled from the epicenter 3. Vancouver 4. Tokyo 5. Easter Island

1. 425 2. 5000 3. This location is most at risk for the tsunami 4. The tsunami hit this location third 5. This location is the least threatened by the tsunami.

Based on your report accessing the risk to Ocean Village, what must Ocean Village do to take advantage of the information you provided?

1. Develop an evacuation plan for those in hazardous areas 2. Be sure Ocean Village is hooked up to the early warning system 3. Educate the populace about tsunamis and the potential threat

1. Tsunami 2. Hurricane/storm surge 3. Both

1. Sudden release of energy from an earthquake causes motion and water movement 1. Travels in wave train away from an epicenter 2. Powerful unrelenting winds force water toward the coastline 2. Long warning times 2. Low atmospheric pressure causes a rise in sea level

_________ is a seismic zone that has not produced a large earthquake for a considerable length of time.

A seismic gap.

What is a tsunami?

A series of water waves that travel away from a fault in all directions at high speed.

Look again at the map. Bear in mind that all the earthquake locations that are not inland are on a convergent plate boundary (Subduction zone). Which of these statements are true?

All of the locations except 9 could produce tsunamis, because all are subduction zones involving at least one oceanic plate.

A tsunami is caused by ___________.

Anything that displaces water.

What type of plate boundary are most tsunamis associated with?

Convergent plate boundaries.

True or False A single tsunami produces one wave, either a local tsunami or a distant tsunami.

False

True or False A tsunami can NEVER strike locations on the East Coast of the United States because there are no subduction zones in the Atlantic Ocean.

False

True or False All tsunamis in recorded history have occurred in the Pacific Ocean.

False

True or False Any earthquake in the oceanic crust has the potential to cause a tsunami to form, it mainly depends on the direction that the rocks move during faulting.

False

True or False Human activities are making tsunamis more common and larger.

False

True or False If Japan had a tsunami warning system, then many of the deaths in the 2011 tsunami would have been prevented.

False

True or False If you can see the tsunami coming, you could probably just wait for it and swim to safety.

False

True or False People on the African Coast only had minutes to prepare for the Indonesian tsunami of 2004.

False

True or False Probability analysis can now tell us precisely when and where a tsunami is likely to occur.

False

True or False The entire eastern US coast has one of the highest threats from tsunamis in the world.

False

True or False There are no natural service functions of tsunamis; they only cause negative impacts such as death and destruction.

False

True or False There is little chance of another devastating tsunami in Indonesia over the next 100 years because of the tsunami in Indonesia within the past 15 years.

False

True or False There is no way to know where a tsunami is likely to occur.

False

True or False Tsunamis in the open ocean are big enough to capsize freighters and other large boats.

False

True or False Usually, there is only one wave from the tsunami and once it recedes people may return to their homes.

False

How might Clearwater River be affected by a tsunami or a storm surge?

In both cases, water will travel upriver and affect areas upstream to the run up elevation.

Why does the wave height of a tsunami increase as the tsunami enters shallow water?

In shallow water, the energy of the tsunami must be contained within a smaller water column.

Which has the potential for greater run up: a category 5 hurricane or a tsunami generated by a large earthquake?

It is impossible to tell; there are other factors to consider.

The Valdez, Alaska, earthquake created a tsunami that caused extensive damage to the Hawaiian Islands. How long did it take the tsunami to reach Hawaii?

Just over 6 hours

If you had been in a boat in the open ocean as the 1960 Concepcion, Chile, earthquake passes, what would have happened to your boat?

Nothing noticeable would have happened

The elevation of Ocean Village has been determined in order to predict the potential risk to tsunamis, but why might this elevation not be accurate after a tsunami?

Ocean Village could be located above a subduction zone. After strain is released at a subduction zone, land elevation lowers. Therefore, more areas may be affected by a tsunami.

Which ocean is associated with the most tsunamis?

Pacific ocean.

Which of the following best describes how scientists help the public prepare for an earthquake event?

Scientists cannot predict when exactly and earthquake will occur, but the can identify tectonically active areas that are likely to produce an earthquake and let the people know they are in an earthquake prone area.

Water run up elevation 10 feet

Site 1 Site 4

No risk for this site

Site 2

Water run up elevation 30 feet

Site 3

Water run up elevation 20 feet

Site 5

Why hasn't the east coast of the United States been affected by tsunamis in recorded history?

The east coast does not have a tectonically active zone offshore to generate tsunamis.

An important reason for the extraordinarily high death toll in the Indonesian tsunami of 2004 around the Indian Ocean was that

There was no warning system to alert people to evacuate.

Will Sumatra experience another tsunami like the destructive one of December 2004?

This is likely, because Sumatra is near many ocean trenches.

How are tsunamis generated?

Through displacement of the seafloor under water.

True or False A locked fault in a subduction zone represents a major threat for producing a large tsunami.

True