Continuation of the notes for the second exam
Tsunamis - Keynote pdf
Most tsunamis are generated by earthquakes.
However, most earthquakes do not generate tsunamis.
Tsunamis are generated when earthquakes fault the sea floor and displace seawater.
When one side of a fracture moves up or down, seawater is displaced and a wave is generated
Tsunami Characteristics
Wave lengths can be greater than 100 km.
Wave speeds can be greater than 700 km/hr.
Typical wave periods are 12-15 minutes.
Wave heights in the open ocean average 1 m.
Tsunamis in Deep Water
Tsunami waves generally are undetectable by ships in deep water.
Sea level will rise and lower 1 m in 12-15 minutes.
Tsunamis in Shallow Water
Tsunami wave heights can increase significantly in nearshore, shallow water.
However, most tsunamis wave do not break like normal wind waves.
Tsunami wave tops can out run the bottom forming a wall of water separating different sea levels.
The wall of water is called a tsunami bore.
Tsunami Runup
Runup is the height above sea level that a wave reaches as it runs up the coastline.
Tsunami waves slow in shallow water but often strike a coastline at speeds greater than 50 mph.
Along flat coastlines, tsunamis waves can travel inland for several miles.
When a wave retreats, it drags debris and humans into the ocean.
Recent Hawai'i Tsunamis
Historically, a large, deadly tsunami strikes the Hawaiian Islands every 25 years.
The last two were in 1946 and 1960.
Hawai’i is overdue statistically for a large, destructive tsunami.
April 1, 1946 Tsunami
A 7.8 magnitude earthquake in the Aleutian Islands generated a Pacific-wide tsunami.
159 people died in Hawai’i.
The runup was 12.0 m in Pololu Valley.
The next slide shows the travel time to Hawai’i.
May 22, 1960 Tsunami
A 9.5 magnitude earthquake in Chile generated a Pacific-wide tsunami.
61 people died in Hawai’i.
The runup in Hilo Bay was 10.7 m.
The next slide shows the travel time to Hawai’i.
The notes for the second exam will be complete the Friday prior to the exam