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Lecture 6

GEOL 106 Lecture 6: Geol week 6

Geological Sciences and Geological Engineering
Course Code
GEOL 106
John Hanes

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Week 6: Tsunamis
Tsunami is Japanese for harbor wave
Caused by a sudden vertical displacement of ocean water
Triggered by:
o Large earthquakes that cause uplift or subsidence of sea floor
Most common cause of Tsunamis
o Landslides (underwater or originating on land)
o Volcano flank collapse
o Submarine volcanic explosion
o Asteroids
Can produce mega tsunami
Earthquake Destruction
What is a tsunami?
o Most are generated by displacement from a megathrust fault
o In open water, the wave amplitude is less than 1 meter and the wavelength can be as large
as several hundred km
o Close to shore, waves slow down and the water piles up, and some tsunamis can exceed 30
meters in height
Earthquakes Caused Tsunamis
Offshore earthquakes can cause tsunamis to go toward land and out to sea
o Uplifted dome of water splits in two waves
Distant tsunami
o Travels out to sea and can travel long distances with little loss of energy
Local tsunami
o Travels towards land very quickly
o People have very little time to react
Tsunami Run-up
Is the furthest horizontal and vertical distance a tsunami travels inland
Regions at Risk
All oceans and some lake shorelines have some risk
Greater risk is for coasts near sources of tsunami
o Earthquakes, landslides, volcanoes
Greatest risk is to areas near or across from subduction zones
o Example: Cascadia zone, Chilean Trench, off Coast of Japan
Areas around Pacific Ocean, Mediterranean, northeastern side of Indian Ocean
Effects of Tsunamis
Primary effects
o Flooding and erosion
Shorten and coastline
Debris erodes both landscape and human structures
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