Exam 3- Envrionmental Hazards

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

true

Which of the following regions has the LEAST risk from tsunamis?

East coast of the U.S

What is "runup"?

The farthest horizontal and vertical distance that tsunami waves move inland

Which shorelines are at greatest risk for tsunamis?

Near subduction zones

Which of the following describes the tsunami in Indonesia in 2004?

M 9 earthquake triggered a 10 m tsunami, which was the deadliest tsunami ever, killing more than 200,000 people in several countries.

Which of the following describes the tsunami in Lituya Bay, Alaska in 1958?

M 7.7 earthquake triggered a massive landslide, which fell into the water and caused water to surge over 500 m (1,700 ft) above the normal water level.

Why don't earthquakes on transform faults trigger tsunamis?

The earthquakes don't vertically displace the water in the ocean

What happens as a tsunami nears land?

The height of the waves increases due to a decrease in both water depth and tsunami velocity

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

false

Why don't boats in the open ocean notice a tsunami approaching?

Tsunamis are too small in amplitude in the open ocean, and the distance between crests is too large to notice its passing.

The Japanese word 'tsunami' literally translates to _____.

large harbor waves

What is the primary physical cause that produces a tsunami?

Sudden vertical displacement of ocean water

Four common triggers for a tsunami:

large earthquakes, underwater landslides, volcanic activities, and asteroid impacts

How does the frequency of asteroid-triggered tsunamis compare to earthquake-triggered tsunamis?

Asteroid-triggered tsunamis are much lower in frequency but can produce mega-tsunamis

A tsunami can cause a catastrophe up to a…

thousand of kilometers from where they originate

What is the mathematical formula used to calculate tsunami velocity (v)?

v= g×D

Tsunami’s energy is dependent on…

wave speed and height

As a tsunami wave approaches the shore, what happens to its velocity and height?

The wave slows down and its height (amplitude) increases.

In the tsunami velocity formula v=

g×D, what does the variable D represent?

depth of water

In the tsunami velocity formula v=

g×D, what value and unit are used for the constant g?

9.8 m/s2(acceleration due to gravity)

How does water depth (D) affect the velocity of a tsunami wave?

The velocity increases as the water depth increases.

What is the approximate average velocity of a tsunami in the deep ocean (average depth of 4,267 m)?

450 to 460 mph (or approximately 205 m/sec)

According to historic records, what percentage of tsunamis are generated by earthquakes?

73%

What type of tectonic environment is responsible for most earthquake-generated tsunamis?

subduction zones

Why do strike-slip earthquakes typically NOT cause tsunamis?

They lack the necessary vertical displacement of the seafloor

What are the two specific mechanisms by which an earthquake can cause a tsunami?

Seafloor movement (vertical shift) or triggering a landslide

What is the minimum earthquake magnitude typically required to create enough seafloor displacement for a tsunami?

m7.5v or greater

What initial water feature forms on the surface directly above a fault rupture during a tsunami's initiation?

an elongated dome

Describe the behavior of tsunami waves in the deep ocean regarding their amplitude and wavelength.

They have small amplitudes (1−3 ft) and very large wavelengths (spacing of approx. 60 miles).

Why do boats in the open ocean often fail to notice a passing tsunami?

the waves have a very small amplitude and extremely long spacing between crests

When a tsunami nears land, what causes the wave amplitude to increase?

The decreasing ocean depth slows the wave, causing water to pile up

What happens to the spacing between wave crests (wavelength) as a tsunami approaches land?

the wavelength decreases

Tsunamis often arrive at the shore as a _____ rather than giant breaking waves.

quick increase in sea level

What is the natural warning signal of an approaching tsunami if the 'trough' of the wave arrives first?

The seawater recedes significantly, exposing the seafloor.

List the four stages of a tsunami's development.

initiation, split, amplification, and runup

In the context of a tsunami, what is the 'split' stage?

The initial dome of water collapses and divides into two waves: one traveling out to sea and one toward land

What is the difference between a 'distant' tsunami and a 'local' tsunami?

A distant tsunami travels across open ocean, while a local tsunami heads toward nearby land with little warning time

The farthest horizontal and vertical distance reached by the largest tsunami wave is called the _____.

runup

What type of water flow occurs when a tsunami wave returns to the ocean after its maximum runup?

strong, turbulent flow

What are 'edge waves' in the context of a tsunami?

waves that travel back and forth parallel to the shore

Regarding duration, how long can tsunami waves continue to strike a coastline?

they can last for hours

How does the motion of a tsunami wave differ from a wind-caused wave near the shoreline?

Wind waves roll forward in circles; tsunami waves flow straight with tremendous momentum

Which 1993 event demonstrated the danger of local tsunamis due to lack of warning time?

The Hokkaido earthquake in the Sea of Japan

What caused the large tsunami in Papua New Guinea in 1998?

A submarine landslide triggered by a M7.1 earthquake

What is the most famous example of a tsunami caused by an on-land rock avalanche?

Lituya Bay, Alaska (1958)

What was the record-breaking surge height at Lituya Bay in 1958?

524 m (1,720 ft)

List three volcanic mechanisms that can generate a tsunami.

explosions, collapses, and avalanches of debris into the water

Which geographic regions face the greatest risk from tsunamis?

Areas near or across from subduction zones

Name three specific major subduction zones capable of generating M9 or greater earthquakes.

cascadia zone, chilean trench, and japan trench

What are 'ghost forests' evidence of in a geologic record?

Coastal land subsidence (sinking) caused by large earthquakes

At what runup height is a tsunami typically considered 'significant'?

5 m (approximately 16 ft) or more

What was the magnitude of the earthquake that caused the 2004 Indian Ocean tsunami?

M9.1+ (or M9.2)

Approximately how many people were killed in the 2004 Indian Ocean tsunami?

230,000 people across 14 countries

What was the primary reason for the high death toll in the 2004 Indian Ocean tsunami despite the available scientific knowledge?

Lack of a warning system in the Indian Ocean and a lack of public education

In the 2004 Sumatra earthquake, how far did the seafloor shift horizontally?

65 ft

What biological precursor was noted before the 2004 tsunami, specifically involving elephants?

They started trumpeting, ignored handlers, and headed for higher ground

What type of sound waves, which humans cannot hear, do earthquakes produce that animals might sense?

Infrasonic sound (low frequency)

Which historic tsunami in 1755 killed about 20,000 people and produced wave heights of 23 ft in the West Indies?

The Lisbon, Portugal earthquake (M9)

Which 1883 event produced 116 ft high waves and killed over 36,000 people?

The Krakatau volcano collapse

Which M9.1 earthquake in 2011 killed over 20,000 people in Japan?

the Tohoku earthquake

In the context of the 2004 tsunami, what 'accommodation space' factor caused waves to get higher near land?

The lack of space below the water's surface as depth decreased

Term: Peak (or Crest)

the highest point of a wave

Term: Trough

the lowest point of a wave

Term: Wavelength

the horizontal distance from one wave peak to the next peak

Term: Period

the time required for one full wave to pass a specific point

Term: Frequency

the number of wave crests passing a point each second

Term: Amplitude

the height of the wave measured from the still water level to the crest

How does coastal vegetation affect tsunami runup?

It can help reduce runup height by providing resistance to the incoming water

Why is the 2004 Indian Ocean tsunami often called the 'Boxing Day tsunami'?

Because it occurred on December 26, which is Boxing Day

During the 2004 'mega-thrust event,' for how long did the rupture last?

several minutes

What was the horizontal length of the rupture in the 2004 Sumatra earthquake?

900 miles

In the 1964 Alaska earthquake, forests near the shoreline sank as much as _____ feet.

10 ft

How do tsunamis affect regions thousands of kilometers away from their origin?

They can maintain enough energy to cause catastrophes at great distances

What happened to the coastal forests in the 1964 Alaska earthquake as the land subsided?

They were drowned by salt marshes and became ghost forests

What determines if a tsunami is classified as a 'mega-tsunami'?

Extremely large wave height, often triggered by asteroid impacts or massive landslides

Which 1960 earthquake recorded at M9+ caused over 61 deaths in Hawaii?

chile earthquake

A tsunami wave travels at approximately _____ mph when it reaches shallow water (20 m depth).

28 to 30 mph

What is the primary danger of the turbulent flow of water returning to the ocean after a tsunami runup?

It carries debris and people back into the sea with great force

In the 1993 Sea of Japan tsunami, how many minutes after the earthquake did the huge waves arrive?

only 2-5 minutes

The 1998 Papua New Guinea tsunami reached a height of _____.

50 ft

What volume of rock fell into the ocean during the 1958 Lituya Bay landslide?

30.5 million m cubed

Why did scientists in Sri Lanka sound a warning during the 2004 tsunami even without a formal system?

They noticed the sea level drop (the receding water precursor)

How can 10-year-olds help in tsunami situations, as seen in the 2004 Thailand case?

Through school education on plate tectonics and recognizing warning signs

What was the vertical seafloor shift during the 2004 Sumatra earthquake?

10-20 ft

According to the provided velocity table, a water depth of 15,000 ft correlates to a tsunami speed of _____.

500 mph

According to the provided velocity table, a water depth of 300 ft correlates to a tsunami speed of _____.

60 mph

Under what condition will the second and third waves of a tsunami be larger than the first?

They may be amplified by interactions like edge waves or coastal shape

What historic tsunami killed over 160 people in the Hawaiian Islands in 1946?

The Aleutians earthquake (M8.1)

Which historic M8.3 earthquake killed 130 people in both Alaska and California?

The 1964 Alaskan Earthquake

The 2010 M8.8 earthquake in Chile killed about 700 people primarily in _____.

coastal towns

In the 1993 Hokkaido tsunami, the town was struck by waves coming around _____ of the island.

both sides

What is the primary reason that distant tsunamis can travel across entire oceans?

They experience very little loss of energy in deep water

What is the primary reason that distant tsunamis can travel across entire oceans?

They experience very little loss of energy in deep water

Submarine landslides occur _____ the water.

underneath

Why is the Cascadia zone specifically mentioned as a high-risk area?

It is a major subduction zone capable of generating M9 earthquakes

In the 2004 tsunami, waves were about _____ feet high when they struck land.

33 ft

What is the relationship between wavelength and amplitude as a tsunami moves into shallower water?

wavelength decreases as amplitude increases

Which tectonic setting is most commonly associated with the generation of tsunamis?

subduction zones

Based on the provided formula, how does the velocity (v) of a tsunami wave change as it moves into shallower water?

velocity decreases as depth decreases