Tsunami key terms

Question 1

Tsunami genesis

Answer 1

• Dome collapse = tsunami wave (aftershocks)
• spacing of waves can be >100km (barley detected in deep ocean)
• shallowing = reduction in speed and wave spacing
• apparent rapid sea level rise rather than wave

Question 2

ocean waves near shore

Answer 2

• As the wave approaches shallow water the shape of the motion becomes more
elliptical and the velocity slows down.
• To conserve energy the wave rises higher

Question 3

tsunami wave height

Answer 3

height of wave at the shore

Question 4

tsunami run-up height

Answer 4

maximum height that the wave reaches on land

Question 5

tsunami locations

Answer 5

• large subducation zones produce the most tsunamis

- pacific has the most (ring of fire)

Question 6

Smaller tsunami wave effects:

Answer 6

• Even small events can generate locally high waves
• In a bay the waves can be focused and increase their
amplitude
• A landslide triggered by an earthquake in a fjord in Alaska in
1958 created waves with a run-up up to 518 m high
• The warning time can be dramatically short

Question 7

Wave diffraction

Answer 7

waves that pass from a media where they move fast to a media where they move more slowly, are refracted and waves that move around obstacles are diffracted.
- this can highly influence the local damaged resulting from the waves

Question 8

tsunami warning

Answer 8

• as soon as an earthquake of magnitude >6.5 is located in the sea the alarm start 
• Using computer simulations and
maps allows forecast the time of
arrival in different locations
• Buoy and tide gauges help to verify
the effective presence of a tsunami
• Initiation of emergency plans

Question 9

Can warning improve?

Answer 9

• Improved sensor networks in hazards areas of the world (seismic, tide
gauge, ocean buoys) and coordinated distribution and processing of
data
• Better information content that can better assist emergency responders
to assess the scope of the disaster
• Coordination and integration with national, regional and local
emergency response agencies and civil authorities
• Education and training at national, regional and local levels of
government and the general population

Question 10

Volcanic induced tsunami

Answer 10

• Anak Krakatau, december, 2018

Question 11

Storegga slides

Answer 11

• largest mass movement event to have effected NW Europe in 50,000 years
• 3 events between 8,000 and 5,000

Question 12

Storegga slide preceding conditions

Answer 12

• sea level lowering (onset glaciation)
• glacial expansion (glaciers extend off shore and sediment flushed out to continental margin
• glacial retreat (unstable, unconsolidated sediment

Question 13

triggers of Storegga

Answer 13

• sediment loading following glaciation
• earthquakes
• M7 inland, result of isostatic rebound following deglaciation
• Gas hydrate melting
• warm water influx after deglaciation affected areas close to head of slide = change in pressure = initiation of slide

Question 14

Seiches

Answer 14

• sloshing of closed water bodies during an earthquake
• large earthquake have produced these observed over large areas
• although seiches have produced waves with height of few feet, damage was minimal