1.
Tsunami
- What is a Tsunami?
- Why are Tsunami so Destructive?
Review for Exam 2
Reading:
4th Ed. Ch 11 Secs 5-10
5th Ed., Ch 10 Secs 24-29
Graphics: (top) Tsunami warning sign, commonly seen on the west coast of the US.
(bottom) Fishing boat beached near a damaged fire truck. Photo by D.J. Sigrist
International Tsunami Info. Center, Honolulu. Courtesy of NOAA.
2. What is a Tsunami?
Tsu = harbor
Nami = wave
- not confined to harbors
- not created by tides
Created by direct displacements of the water's surface via undersea earthquakes,
landslides or volcanic activity
Energy travels outward (like ripples that spread when a rock is thrown into a
pond)
Graphic: Valdez, Alaska following a tsunami generated by the March 27, 1964
earthquake. Photo courtesy of U.S. Dept. of Interior.
3. Aleutian Trench Tsunami - April 1946
- Caused by an earthquake that displaced the sea floor
- Significant damage in the Aleutians and Hawaii
Graphic: Garrison, 4th Ed., Fig. 11.5, pg 264, 5th Ed., Fig. 10.30, pg 248.
4. The Indian Ocean Tsunami – The Earthquake
Graphics: (top) Location of the Sumatra earthquake, courtesy of USGS, (bottom)
Seismogram of the Sumatra earthquake measured at Middletown, PA, courtesy of
Pennsylvania Geological Survey.
5. How can an Earthquake Trigger a Tsunami?
At subduction zones, plates don’t usually move gradually- they can “lock”
Infrequent large earthquakes can suddenly release the accumulated strain
When sudden plate motion deforms an area of the seafloor, a large volume of
ocean water is displaced… this is the beginning of a tsunami
Graphic: Courtesy of the Pacific Tsunami Warning Center.
6. How did the Indian Ocean Tsunami Move?
Tsunami are a series of waves that radiate away from where they are generated
As they travel, they can bend and their speed can change due to the shape of the
basin (they are shallow water waves)
Animation courtesy of the National Institute of Advanced Industrial Science and
Technology, Japan.
7. What Happens as a Tsunami Moves Ashore?
In deep water – tsunami have small wave height and long wavelength
As a tsunamis move toward shore, its wavelength decreases and it grows much
higher and steeper
Graphic courtesy of the Pacific Tsunami Warning Center.
8. Banda Aceh – Before and After
Coastline geometry and distance from the triggering event determine the height
of a tsunami; many factors, such as population density, land use and building
techniques, determine the level of destruction caused by a tsunami
Graphic: Aceh Province, Sumatra, Indonesia, IKONOS images, provided courtesy of
Space Imaging/CRISP-Singapore.
9. Tsunami Ashore
Tsunami wash ashore as a series of waves
- Crests and troughs are usually separated by ~15 minute intervals
- The trough can arrive before the crest
Onshore, tsunami often appear as a very rapidly moving, very high tide
Wave heights at the shore can be 30 meters (or larger)
Graphic: Garrison, 4th Ed., Fig. 11.7, pg 266, 5th Ed., Fig. 10.32, pg 250.
10. The Tsunami Warning System
Objective = predict the intensity and time of arrival of tsunami generated by
earthquakes
Anchored instruments measure sea level changes as tsunami pass over
Warnings and watches issued based on predicted arrival times
Graphic: Deep Ocean Assessment and Reporting on Tsunami (DART) buoy. Courtesy of
NOAA.
11. Tsunami and the Pacific
Common in the Pacific due to seismic activity at subduction zones
Travel times calculated based on the time of the triggering event
Tsunami can reflect off land masses - the reflection can result in an area being
affected by the same tsunami twice!
Graphic: Map of travel times for tsunami generated by earthquakes in Alaska and
Chile, courtesy of USGS.
12. Exam 2 Overview
Tuesday Mar 6
Worth up to 26% of your grade; your lowest midterm score is dropped
Be on time! Bring two pencils and an eraser!
Format: (1) Multiple choice (~50-60 questions) except for late arrivals (2)
Students arriving late will take a short-answer and essay exam on the same
material (3) May include interpretation of maps and diagrams
Content: Lectures 8-13 (inclusive), Marine Pollution through Tsunami