Tsunami Flashcards

Question

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

Answer 1

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)

Answer 2

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)

Answer 3

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)

Answer 4

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

Answer 5

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

Answer 6

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

Answer 7

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

Answer 8

Earthquakes (72%) Landslides (10%) Volcanoes (5%) Other or Unknown (13%)

Answer 9

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)

Answer 10

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)

Answer 11

Nuclear testing in the U.S. in the 1940s and 1950s has generated tsunami in the past Halifax explosion, 1917 generated small localized waves

Answer 12

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

Answer 13

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

Answer 14

"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.””

Answer 15

Return period <500 years Located within or directly in the path of tsunami from active subduction zones (M9 earthquakes)

Answer 16

Return period of 500-2000 years Located adjacent to active continental faulting or in regions of moderate distance from active subduction zones

Answer 17

Return period of 2000+ years Coastal areas subject to effects from submarine slides, volcanic landslides, or infrequent but large earthquakes

Answer 18

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)

Answer 19

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

Answer 20

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

Answer 21

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)

Answer 22

Low risk (no historical tsunami or prehistoric deposits) Presence of sea ice reduces risk

Answer 23

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)

Answer 24

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

Answer 25

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

Answer 26

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.

Answer 27

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

Answer 28

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

Answer 29

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

Answer 30

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!

Answer 31

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

Answer 32

May be costly to build and upkeep Could protect large populations Could be overtopped by large tsunami Subject to scouring at the base

Answer 33

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

Answer 34

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

Answer 35

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

Answer 36

Disease outbreaks (cholera, malaria) Loss of shelter, crime, mental trauma Economic vulnerability of communities dependent on tourism, fishing, or agriculture

Answer 37

Earthquake monitoring Tsunami warning systems

Answer 38

Building codes for susceptible coastline areas | Use of natural vegetative barriers

Answer 39

Identify potential earthquake sources Map prehistoric tsunami deposits (local and teletsunami) Tsunami inundation maps

Answer 40

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

Answer 41

Ocean-wide (e.g.) Pacific Tsunami Warning Center, Hawaii Regional (e.g. West Coast & Alaska Warning System) Local (e.g. BC Provincial Emergency Program)

Answer 42

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)

Answer 43

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

Answer 44

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

Answer 45

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

Answer 46

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

Answer 47

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

Answer 48

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