Tsuamis Flashcards
definition of tsunamis
Giant sea waves generated by shallow focus underwater EQs, volcanic Europe’s and large land slides into sea.
Biggest cause of tsunamis
Earthquake
Characteristics
Long wavelength - 100km+
Low wave height - under 1m in open sea
Travel quickly at 700km/hr
(This changes when waves get to shallow water )
First obvious sign of tsunami occurrence ?
Wave trough in front of tsunami results in reduction in sea level - drawback.
What is actual tsunami like ?
Large waves over 25m height.
Several waves - the largest not necessarily the worst.
When the tsunami reaches the land, what will its effects depend on ?
Height of the wave / distance travelled.
Length of event from source.
Extent to which warnings are given.
Physical coastal geography ( offshore& on coastal area )
Coastal land use / density
Impacts
People drown in water
Injury from debris in water
Buildings/ roads / bridges washes away.
(Have impact at least 500-600m inland)
Krakatoa 1883
Drowned 35,000 people
Produced waves that travelled around the world.
40m waves
Where are most tsunamis generated ?
90% in Pacific basin associated with tectonic activity.
Most at destructive plate boundaries where subduction occurs - causes plates to lift and displacement of water.
Western side of Pacific
Eastern side of Indian Ocean (25%)
Name 3 tsunami events ?
Boxing Day tsunami 2004
South java coast 2006
Solomon Islands 2007
Soloman island tsunami
2007
8 magnitude
Killed 15 people
Why are tsunamis not great ?
Hard to predict
Even if magnitude and EQ location is known
How to predict tsunamis ?
Automated systems installed to give warnings.
Bottom pressure sensors attached to buoys , measure pressure of overlying water Column.
Warning systems in high risk areas.
Example of monitoring system
The Pacific warning system based in Hawaii.
Monitors EQ activity and issues warning to counties around Pacific edge.
Near by counties built 12m walls
