Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

GEOG 235 > Tsunami > Flashcards

Tsunami Flashcards

1
Q

Tsunami Definition

A

A series of shallow water waves generated by the sudden displacement of a large body of water, usually an ocean but may occur in seas, bays, lakes, rivers, fjords

Not “tidal waves” which would imply tsunami are related to the tides of the Earth

Not “seismic waves” as tsunami may be triggered by other mechanisms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Classification of Waves

A

Wavelength
Period
Cause

-For example, tides are generated by gravity, wind-generated waves by fetch, and tsunami by the displacement of large bodies of water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Wavelength

A

the distance between two identical points on a wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Height

A

measured from the base of the trough to the crest of the wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Amplitude

A

the height of the wave measured from the still water level line (equal to ½ the wave height)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Period

A

refers to the time between two successive waves at a stationary point

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Velocity

A

refers to the speed at which the wave travels (dependent on water depth)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Wind-Generated Waves

A

Affect the uppermost layer of water only

Caused by wind

Wavelength in metres

Period in seconds

Travel at low speeds

Break when the reach the shore, dissipating their energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Tsunami Waves

A

Involve the motion of the entire water column from surface to sea-floor

Caused by the large displacement of water

Wavelength in kilometers

Period in minutes

Travel at high speeds

Do not break when they reach the shore, resulting in a wall of water that runs over normally dry land

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Causes of Tsunami

A

Tsunami are most commonly generated by underwater shallow-focus earthquakes which cause the rise and fall of the ocean floor.

This movement triggers the displacement of large bodies of water which travel as a series of waves thousands of kilometers from their source.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

In addition to earthquakes tsunami may be triggered by:

A

landslides, submarine slumps, rock falls, and avalanches

explosive volcanic eruptions or flank collapses

human-caused explosions

meteorite impacts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

There are 4 important stages to consider from the time the tsunami is generated to its arrival on land:
Generation

A

the upward or downward movement of the ocean floor produces waves that spread outward from the source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

There are 4 important stages to consider from the time the tsunami is generated to its arrival on land:
Propagation

A

the waves spread out in all directions from the point of initiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

There are 4 important stages to consider from the time the tsunami is generated to its arrival on land:
Inundation

A

how tsunami waves behave as they approach land and inundate coastlines

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

There are 4 important stages to consider from the time the tsunami is generated to its arrival on land:
Aftermath

A

how tsunami waves behave on land including risk factors and mitigation strategies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Generation

A

Vertical motion associated with underwater faults sets in motion tsunami waves that transmit energy outwards and upwards from the source

Thrust and reverse faults at subduction zones may displace large volumes of water in this way, resulting in tsunami

Normal faults may also displace large volumes of water and generate tsunami

Horizontal movement on strike-slip faults does not displace water to produce tsunami

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

The size of tsunami waves thus depends on the following factors:

A

magnitude of the shallow-focus earthquake (M7 and above)

area of the rupture zone

rate and volume of water that is displaced

depth of water above the rupture

nature of motion of the ocean floor

vertical offset or displacement of the fault

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Propagation

A

Propagation refers to any of the ways in which waves travel

From a hazards perspective we are most interested in understanding how fast and how far tsunami waves travel so we can anticipate impact on coastlines

Celerity refers to the velocity of wave propagation

Tsunami waves have been known to travel across the Indian Ocean in less than one day (e.g. Indian Ocean tsunami of 2004)

Wave directions may change as the waves reflect or diffract in response to the topography

The rate at which waves lose their energy is inversely related to their wavelength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

The velocity of shallow water waves such as tsunami depends on the water depth and gravity:

A

C = √(g*d)

where C = velocity in meters per second,
g = gravitational acceleration (9.8 m/sec2),
d = depth in meters

Tsunamis travel much faster in deep ocean than closer to shore

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Bathymetry

A

(from the Greek “bathus” or deep and “metron” or measure) is the study of landforms of the ocean floor

Bathymetric data is used to help predict the coastal regions that will be most affected as well as the arrival times of tsunami traveling across the ocean

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Shoaling

A

means that tsunami waves are very destructive when they arrive on shore, even thousands of km away from their origin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Inundation

A

Inundation refers to how tsunami waves behave as they approach land and inundate coastlines

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Tsunami hazard is evaluated by maximum wave run-up which may be measured as:

A

Inundation: refers to the horizontal distance that the waves flood inland

Run-up: refers to the vertical inundation or the height of the incoming waves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Inundation and run-up are affected by:

A

Shoaling: amplitude and height of the waves increase as the waves reach the shoreline

Coastal/Bathymetric Topography: this includes factors such as:

  • variations in elevation as the tsunami moves from deep ocean to shore
  • interaction of tsunami waves with steep coastlines (reflection)
  • diffraction that occurs around reefs, and other barriers

the period of a bay, basin, inlet, or harbor (resonance; interference)

interference of wave patterns as tsunami waves interact with edge waves and each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

There are 4 types of behaviour when waves interact with coastal or bathymetric topography:

A

Reflection- depends on the shape of the coastline and the presence/absence of barriers

Refraction- as waves move from deep to shallow water their velocity and wavelength decrease, wave height increases and the direction of wave motion changes

Diffraction- occurs when the waves encounter a barrier; the waves bend and change direction as they travel around the barrier

Interference- occurs when two waves interact with each other, forming new wave patterns (also causes resonance)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Some locations along the coast are prone to more inundation or run-up than others

A

exposed ocean or barrier beaches (inundation)

cleared land for agriculture or development (smooth topography) (inundation)

river deltas (run-up)

headlands (run-up)

bays and harbors (resonance)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Resonance

A

Resonance occurs in bays and harbors due to the long periods of tsunami waves

In most cases when tsunami waves enter a bay or harbor their energy is dissipated around the whole bay

If, however, the period of the tsunami wave is a multiple of the natural resonance frequency of the harbor, then interference will occur

This will result in seiche, or very large waves produced by many waves combining together

The word tsunami literally means “harbor wave” because of this phenomenon (Bryant, 2008)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Hilo Bay, on the Big Island of Hawaii is famous for tsunami resonating within its harbor:

A

Hilo Bay naturally resonates with a period of 30 minutes

Any tsunami with multiples of this period (i.e. 15 min, 30 min, or 1 hour) will resonate within Hilo Bay

Resonance in harbors can occur for as long as 6 to 24 hours

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Aftermath of Tsunami

A

A popular misconception is that a tsunami is a single wave

Instead, tsunami are a series of waves separated by long periods from 10 minutes to 2 hours

The first wave is commonly not the highest; interaction with edge waves increases amplitude

Edge waves are created by refraction that occurs along the shoreline

When tsunami waves arrive on shore, they may appear either as a series of waves or a bore

30
Q

Bore

A

A bore is a step-like wave with a steep breaking front created when one wave overtakes another

31
Q

Drawdown

A

if the trough of the wave hits the shoreline first (as opposed to the crest), the water may withdraw with a hissing or roaring noise and the seafloor may be exposed

Drawdown may occur anywhere from 1 minute to 1 hour before the arrival of the first wave

32
Q

Other Causes of Tsunamis

A

Earthquakes (72%)

Landslides (10%)

Volcanoes (5%)

Other or Unknown (13%)

33
Q

Landslide-Triggered Tsunami

A

Landslides, submarine slumps, rock falls, and avalanches may trigger tsunami if the debris displaces a large enough volume of water (oceans, rivers, bays, lakes, fjords)

These mass wasting events are often triggered by earthquakes

Typically these tsunami are localized and much smaller than the tsunami that occur in the ocean

The risk of tsunami is the greatest along steep coasts where large volumes of debris accumulate at high altitudes (e.g. British Columbia)

Famous examples include Lituya Bay, Alaska in 1958 (rockfall) and Grand Banks, Nfld in 1929 (submarine slump)

34
Q

Volcano-Triggered Tsunami

A

Less commonly, tsunami are produced in association with volcanic activity

The most common mechanism is when pyroclastic flows are blasted or flow down the flanks of the volcano displacing large volumes of water (e.g. Krakatau, 1883 generated a tsunami with waves up to 30 m)

These tsunami rapidly decrease in size away from volcano

Tsunami may also be generated due to landslides that could occur on the submerged flanks of volcanoes (Clague, Munroe, and Murty, 2003)

35
Q

Human Caused Explosions

A

Nuclear testing in the U.S. in the 1940s and 1950s has generated tsunami in the past

Halifax explosion, 1917 generated small localized waves

36
Q

Meteorite Impacts

A

No historic examples

However, there are tsunami deposits that are associated with the Yucatan meteorite impact at the end of the Cretaceous period, ~ 65 million years ago

37
Q

The Dangers of Tsunami

A

Tsunami waves will travel long distances without losing their energy

Intense hydrodynamic forces can destroy or lift buildings and houses from their foundations

Tsunami naturally occur at the same time as other natural hazards (large earthquakes, landslides, volcanic eruptions)

Tsunami can have unanticipated secondary effects

Tsunami have long recurrence intervals

38
Q

Tsunami “Stones”

A

“At the edge of Aneyoshi, a small village on Japan’s northeastern coast, a 10-foot-tall stone tablet stands, carved with a dire warning to locals…”

“High dwellings are the peace and harmony of our descendants,” the rock slab says. “Remember the calamity of the great tsunamis. Do not build any homes below this point.””

39
Q

Global Regions at Risk

Greatest Hazard

A

Return period <500 years

Located within or directly in the path of tsunami from active subduction zones (M9 earthquakes)

40
Q

Global Regions at Risk

Significant Hazard

A

Return period of 500-2000 years

Located adjacent to active continental faulting or in regions of moderate distance from active subduction zones

41
Q

Global Regions at Risk

Low Hazard

A

Return period of 2000+ years

Coastal areas subject to effects from submarine slides, volcanic landslides, or infrequent but large earthquakes

42
Q

Distant tsunami (teletsunami)

A

tsunami that originate from distant sources, generally more than 1,000 km away (e.g. 1964 Vancouver Island)

Teletsunami are capable of producing both distant and local effects (e.g. 1700 Cascadia)

43
Q

Local tsunami-

A

tsunami that originate from nearby sources, generally within 100km (e.g. Lituya Bay, Alaska)

Generally includes tsunami generated by landslides and volcanic eruptions

Local tsunami have shorter periods and do not last as long as distant tsunami

44
Q

Tsunami Risk in Canada

Pacific Coast

A

Tsunami produced by M8 earthquake at the Cascadia subduction zone

Teletsunami generated within the Pacific Ring of Fire (e.g. 1964 Vancouver Island)

Local tsunami triggered by landslides (e.g. 1975 Kitimat Inlet submarine slide)

Greatest risk is to communities located in inlets or along the coast of western Vancouver Island including Tofino, Ucluelet, and Port Alberni

45
Q

Tsunami Risk in Canada

Atlantic Coast

A

Halifax Explosion, 1917
1929 Grand Banks submarine slump and tsunami

Very little evidence of prehistoric tsunami deposits

It’s possible that teletsunami generated by large earthquakes in the Atlantic Ocean could affect the Atlantic coast (e.g. 1755 Lisbon, Portugal)

46
Q

Tsunami Risk in Canada

Arctic Coast

A

Low risk (no historical tsunami or prehistoric deposits)

Presence of sea ice reduces risk

47
Q

Tsunami Risk in Canada

Interior Waterways

A

Steep unstable slopes in alpine areas

Lakes containing unstable delta sediments (e.g. in 1908, a landslide on the Liève River, western Quebec produced a tsunami that killed 27 people)

48
Q

Primary Effects of Tsunamis

A

Impact from the onrushing waves and debris

  • Human impact (deaths and injury)
  • Hydrostatic forces
  • Buoyancy
  • Hydrodynamic forces
  • Debris impact

Flooding and erosion

  • Damage of ecosystems
  • Coseismic subsidence
49
Q

Human Impact

A

Majority of tsunami deaths are by drowning or physical impacts with stationary or floating debris

Often floating debris or people will be swept out to the ocean by the outflow

Tsunami waves are usually tens of meters in height

Compared to a small structure which is ~ 8m (25 ft) in height

50
Q

Vertical evacuation shelters

A

like these have sufficient height to elevate evacuees, and are structurally designed to resist the effects of tsunami waves. They are most useful when there is not enough evacuation time prior to the tsunami warning.

51
Q

Buildings must be constructed to withstand:

A

Hydrostatic forces may cause pressure on walls from variations on water depths on either side

Buoyancy may cause flotation or uplift

Hydrodynamic forces are caused by the impact of the waves on the building and the drag/overturning forces produced as the waves flow around the building

Debris impact is caused by floating objects

Scour erodes around the foundations of buildings

52
Q

Mitigation Strategies

A

Reduce land development or change zoning practices in tsunami inundation zones
Reduce the amount of critical infrastructure (e.g. roads, hospitals, schools, etc) in areas <300m from the coast

Raise existing buildings above expected inundation levels (e.g. raising homes on stilts)

Build multistory buildings (if necessary) in inundation zones that are made with steel and reinforced concrete

Anchor buildings to foundations
To protect against hydrostatic forces, provide openings in buildings so water can reach equal heights within and outside of buildings

Use deep piles and piers to protect against scour

53
Q

Mitigation Strategy

A

A change to zoning regulations could allow for low density development in tsunami inundation zones.

54
Q

Hydrodynamic Forces

A

The power of the waves is immense (Chang 2011):

(e.g.) a wall of water 3 feet X 3 feet X 3 feet = 1700 pounds weighs about the same as a smart car

Now imagine this wall of water traveling at 48 km/hr towards you!

55
Q

Natural Barriers

A

Mangroves are naturally growing trees and shrubs in the intertidal coastal zone

In some cases, houses and other small structures are spared damage due to the protection from mangroves or rows of trees

A mitigation strategy would be to locate infrastructure inland and adjacent to natural vegetative barriers

However, many regions repeatedly remove mangroves to allow for development of homes, hotels, and tourist facilities on the beach

56
Q

Man-Made Barriers

A

May be costly to build and upkeep

Could protect large populations

Could be overtopped by large tsunami

Subject to scouring at the base

57
Q

Damage to Ecosystems

A

Crops could be destroyed due to saltwater

Oil leaks (e.g. 8 million litres of oil escaped from oil plants in Indonesia during the 2004 Indian Ocean tsunami)

Natural vegetative barriers along the coast may be destroyed

Coral reefs and coastal wetlands could also be damaged
58
Q

Flooding and Subsidence

A

Flooding may occur up to 300 metres inland

Mitigation strategies could include: raising buildings above inundation levels, locating mechanical and electrical equipment at higher levels in buildings, protecting critical infrastructure with sea walls (e.g. hazardous material storage facilities)

Coseismic subsidence of 1-2 metres was seen along the northwest coast of Sumatra during the 2004 Indian Ocean tsunami

59
Q

Secondary effects of Tsunamis

A

Fires (caused by spread of liquid contaminants)

Radiation release (e.g. Fukushima 2010)

Contamination of water and soils

Environmental impacts of floating rafts of debris

60
Q

Tertiary effects of tsunamis

A

Disease outbreaks (cholera, malaria)

Loss of shelter, crime, mental trauma

Economic vulnerability of communities dependent on tourism, fishing, or agriculture

61
Q

Early detection and warning

A

Earthquake monitoring

Tsunami warning systems

62
Q

Mitigation strategies for land use and structural controls

A

Building codes for susceptible coastline areas

Use of natural vegetative barriers

63
Q

Probability analysis

A

Identify potential earthquake sources

Map prehistoric tsunami deposits (local and teletsunami)

Tsunami inundation maps

64
Q

Reducing Tsunami Hazards

A
  1. Early detection and warning
  2. Mitigation strategies for land use and structural controls
  3. Probability Analysis
  4. Education and Tsunami Readiness
65
Q

Three types of warning systems for Tsunamis

A

Ocean-wide (e.g.) Pacific Tsunami Warning Center, Hawaii

Regional (e.g. West Coast & Alaska Warning System)

Local (e.g. BC Provincial Emergency Program)

66
Q

Lessons Learned from Past Tsunamis

A

An early detection warning system could have potentially saved many thousands of lives during the Indian Ocean tsunami

Warning systems need to be coupled with earthquake and tsunami education and preparedness (e.g. Japan, 2011)

67
Q

Inundation Maps

A

Risk may be assessed by assessing the size, frequency, and probable impact of tsunami on coastal communities (Clague, Munro, and Murty, 2003)

Inundation maps have been produced for high risk areas in Canada to increase hazards awareness and to inform land planning

Inundation and maximum run-up values are calculated from numerical models and based on tsunami deposits in the geological record

68
Q

Tsunami Readiness

A

Establish 24-hour emergency operation centres

Clearly communicate what tsunami warnings mean

Have ways to alert the public

Develop a preparedness plan with emergency drills

Promote community awareness programs through education

69
Q

Protecting Yourself & Others

A

Be aware of natural warning signs

Heed official warnings; tell others about the danger

Play it safe, even after you think the danger has passed

Expect many waves

Move uphill, inland and away from harbors

Don’t wait or watch the wave- tsunami move fast!

Prepare for blocked or broken roads

If trapped go to the top or roof of a building, climb a tree, or climb onto something that you can use as a raft

Stay clear of debris

Be aware of inundation zones and hazards when you are in tsunami country

70
Q

Tsunami Strikes Thailand

December 24th 2004 M9.1 Earthquake Generated Tsunami

A

Other areas with high risk include eastern Indian Ocean

The past is the key to the present axiom doesn’t always work when dealing with long time scales

No warning system in place like Pacific Ocean

71
Q

Why was the Sumatra tsunami so deadly?

A

High population density on low-lying areas of Indian Ocean

Short distance from tsunami source to populated low lying coasts, leaving little time for warning

Distant tsunami (tele-tsunami): source of the tsunami more than 1,000 km away from the area of interest

Regional/local tsunami: source of the tsunami within 1,000 km of interest

No tsunami warning system in Indian Ocean in 2004

Poor and developing countries with vulnerable infrastructure

Low awareness/preparedness of tsunami hazard

72
Q

Japan Tsunami

A

Occurred on March 11, 2011, killing ~ 16,000 people

Source was a M 9.0 earthquake beneath the seafloor
Subduction zone east of Honshu Island

The direct damage from the earthquake and tsunami was U.S. $235 billion
Most expensive natural disaster in history

Occurred on March 11, 2011, killing ~ 16,000 people

Source was a M 9.0 earthquake beneath the seafloor
Subduction zone east of Honshu Island

The direct damage from the earthquake and tsunami was U.S. $235 billion
Most expensive natural disaster in history

GEOG 235 (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions