Learning Objectives
After reading and studying this chapter, students should
▪ Understand the process of tsunami formation and development.
▪ Understand the effects of tsunamis and the hazards they pose to coastal regions.
Chapter Summary
This concise chapter addresses the mechanisms and hazards of tsunamis, and the solutions to reducing
the resulting death and destruction. The chapter opens with a detailed case history of the 2004 Indian
Ocean tsunami, which killed at least 230,000 people. Following sections focus on processes of
tsunami origin, historic tsunamis, regions at risk, and the linkages between tsunamis and other natural
hazards. The chapter closes with discussions of tsunami hazard reduction strategies, and the personal
responses to and perceptions of the tsunami hazard.
Chapter Outline
I. Tsunami
A. Tsunamis
2. originate when ocean water is suddenly vertically displaced
3. can cause catastrophe thousands of km from where they originate
B. Tsunami triggers
1. large earthquake causing rapid subsidence or uplift of seafloor (most common mechanism)
3. volcano collapse or underwater volcanic explosion
4. ocean impact of asteroid or comet (can produce megatsunami)
C. Historic tsunamis
D. How do earthquakes cause a tsunami?
2. generally need earthquake > 7.5 to generate damaging tsunami
4. fast, long waves on open ocean slow and grow vertically when they reach shallow water
6. first wave may be meters to tens of meters high and destroy everything in its path
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Tsunamis
8. arrival times can be predicted accurately, making tsunami warning systems potentially
effective
E. How do landslides cause a tsunami?
1. submarine landslides, or terrestrial rock avalanches falling into the sea, usually generated by
earthquake
2. examples: 1998 New Guinea and 1958 Lituya Bay, Alaska
II. Regions at risk
A. heightened risk of tsunamis from location of coast relative to potential tsunami sources
B. greatest risk adjacent to major subduction zones with convergence of a few cm per year
C. tsunami heights
2. runup height at least 5 m are considered significant tsunamis
4. zones of greatest hazard around Pacific Ocean, also Mediterranean Sea and Indian Ocean
6. Cascadia subduction zone earthquake of 1700 first recognized in coastal sediments, dated
with precision from tsunami recorded in Japan
III. Effects of tsunamis and linkages to other natural hazards
A. Primary effects
1. inundation, flooding and erosion
3. debris carried by the water can cause much damage
B. Secondary effects: minutes to weeks following the event
2. polluted water supplies
3. disease outbreaks
C. Linkages to other natural hazards
1. earthquake shaking causes property damage and ground subsidence
3. volcanic explosions
4. meteorite impacts
IV. Minimizing the tsunami hazard
A. People living on coasts with elevated tsunami risk are more likely to be affected
B. Lessons learned from past tsunamis can be applied to reduce future tsunami damage
1. coastal tree buffer zones
3. warning and evacuation
C. Strategies for minimizing the tsunami hazard
2. structural control
4. land use
6. education: tsunami watches and warnings
7. tsunami-ready status: communities must:
a. establish an emergency operation center with 24-hour capability
b. have ways to receive tsunami warnings from government agencies
Chapter 7 – Instructor’s Manual
V. Perception and personal adjustment to the tsunami hazard
A. Actions when warning issued
2. if tsunami trough arrives first, ocean will recede; run from beach
4. stay out of danger zones until clearance is given, to avoid additional waves
6. don’t go to the beach to watch a tsunami
Answers to Review Questions and Critical Thinking Questions
Review Questions
1. A tsunami is an earthquake-generated sea wave, produced through rupture of the seafloor and
displacement of the overlying water body.
5. The principal direct relationship between plate tectonics and tsunamis is the prevalence of tsunami
6. Tsunamis are detected in the open ocean using surface buoys with a bottom sensor, known as a
7. A tsunami watch is a notification that an earthquake that can cause a tsunami has occurred, while a
8. The major primary effects of a tsunami are inundation and severe damage to structures and the
9. Tsunami hazards can be minimized by identifying tsunami-prone areas and invoking land use
Critical Thinking Questions
1. Such an education program should focus on an understanding of the processes and threats of local
2. A response to this question will hinge on the student’s perception of the media and its ability to
3. A response to this question should address issues of emergency preparedness, public education,
4. People might be better educated about the tsunami hazard through strong science education in the
general population, coupled with accurate but understandable information on where and how
5. The public generally understands that tsunamis are generated by earthquakes, but may not
6. The potential gains of large scale planting of trees would be to disperse and weaken tsunami waves
as they come onshore. The potential losses might be that much of the damage in tsunamis arises