2. Learning Objectives
Explain the process of tsunami formation and development.
Locate on a map the geographic regions that are risk tsunamis.
Synthesize the effects of tsunamis and the hazards they pose to coastal regions.
Summarize the linkages between tsunamis and the and other natural hazards.

3. Learning Objectives, cont.
Tsunamis are not caused by or affected by human activities, but damages are compounded as coastal populations increase.
Discuss what nations, communities, and individuals can do to minimize the tsunami hazard.
Identify the actions you should take and not take if a tsunami warning is issued.

4. Japan 2011: Tsunami and Nuclear Disaster
Pacific Ocean bottom vertically displaced as much as 9 m (~30 ft)
Automated warning system alerted within seconds
Move to high ground
Nuclear plants shut down
Seawall did not keep water out
Nuclear plant flooded
Pumps inundated by seawater
Cooling systems failed

5. 4.1 Introduction to Tsunamis
Tsunami is Japanese for “harbor wave”
Caused by a sudden vertical displacement of ocean water
Triggered by:
Large earthquakes that cause uplift or subsidence of sea floor
Underwater landslides
Volcano Flank Collapse
Submarine volcanic explosion
Asteroids
Can produce Mega-tsunami

6. 4.1 Introduction to Tsunamis, cont.
Some Historic Tsunamis
Date
Cause
Damage
1755
Earthquake(M 9) in Lisbon, Portugal
Killed about 20,000 people, wave heights of 23 ft or more in West Indies
1883
Volcano Collapse
>36,000 people killed, 116 ft high waves
1946
Earthquake (M 8.1) in Aleutians
>160 people killed in Hawaiian Islands
1960
Earthquake (M 9+) in Chile
>61 people killed in Hawaii
1964
Alaskan Earthquake (M 8.3)
130 people killed in Alaska and California
1993
Earthquake (M 7.8) in Sea of Japan
Killed 120 people in Okushiri Island, Japan
1998
Submarine Landslide triggered by earthquake in Papua New Guinea (M 7.1)
Killed >2100 people
2004
Sumatran earthquake (M 9.1+)
Killed > 230,000 people
2009
Earthquake (M 8.1) in Samoa
Killed about 200 people
2010
Earthquake (M 8.8) in Chile
Killed about 700 people in coastal towns
2011
Earthquake (M 9.1) in Japan
Killed > 20,000 people

7. How Do Earthquakes Cause a Tsunami?
Two mechanisms
Seafloor movement (more common)
Triggering a landslide
Takes an earthquake of M 7.5 or greater
Creates enough displacement of the seafloor
Upward or downward movement displace the entire mass of water
Starts a four-stage process

8. How Do Earthquakes Cause a Tsunami? cont.
Earthquake uplifts or downshifts the seafloor
Rupture uplifts the seafloor
A dome forms on the surface of the water above the fault
Dome collapses and generates the tsunami wave
Waves radiate outward (like a pebble in a pond)
Tsunami moves rapidly in deep ocean
Can travel 720 km (450 mi.) per hour
Spacing (frequency) of crests is large and small amplitude
Boats in open ocean don’t notice the tsunami waves

9. How Do Earthquakes Cause a Tsunami? cont.
Tsunami nears land, loses speed, gains height
Depth of ocean decreases, slowing tsunami waves 45 km (28 mi.) per hour
More water piles up increasing amplitudes and frequency
Tsunami moves inland destroying everything in its path
Can be meters to tens of meters high
Often arrives as a quick increase in sea level
Trough may arrive first, exposing seafloor
Runup, furthest horizontal and vertical distance of the largest wave
Water returns to ocean in a strong, turbulent flow
Edge waves may be generated parallel to the shore
Second and third waves may be amplified

10. Tsunami

11. How Do Earthquakes Cause a Tsunami? cont.
Offshore earthquakes can cause tsunamis to go toward land and out to sea
Uplifted dome of water splits in two waves
Distant tsunami
Travels out to sea and can travel long distances with little loss of energy
Local tsunami
Travels towards land very quickly
People have very little time to react

12. Distant and Local Tsunamis

13. How Do Landslides Cause a Tsunami?
Submarine landslides occur when landslides occur underneath the water
Displaces water vertically causing landslides
On land, rock avalanches from mountains can cause tsunami
Example: Lituya Bay, Alaska
30.5 million cubic meters of rock fell into ocean
Bay water surged to 524 m (1790 ft.) above normal

14. 4.2 Geographic Regions at Risk from Tsunamis
All oceans and some lake shorelines have some risk
Greater risk is for coasts near sources of tsunamis
Greatest risk is to areas near or across from subduction zones
Example: Cascadia zone, Chilean Trench, off Coast of Japan

15. Global Tsunami Hazard

17. Case Study 4.2 Indonesian Tsunami
World’s largest earthquake in past four decades triggered tsunami
Was a “megathrust event”
Most lethal tsunami in recorded history
No warning system in Indian Ocean
Few people knew what tsunami meant prior to event
Education (or lack of) was a major reason for so many deaths
Many did not know how to recognize a tsunami
Many went to beach to watch
Few knew what to do
Tourists and first-generation residents

18. 2004 Tsunami Killed People on Both Sides of Indian Ocean

19. Case Study 4.2 Indonesian Tsunami, cont.
Those that were educated
10-year-old British girl
Learned in school about plate tectonics just before going to Thailand
Sounded warning and allowed 100 people to evacuate
Scientists on beach in Sri Lanka
Noticed the sea level drop
Sounded warning for those that went to beach to watch
Animal behavior
Elephants started trumpeting about time of earthquake
Ignored handlers and headed up hill
Education of tsunami could have saved thousands more, especially with the distant tsunamis

20. Tourists Running for Their Lives

21. 4.3 Effects of Tsunamis and Linkages with Other Natural Hazards
Primary effects
Inundation of water and resulting flooding and erosion
Shorten the coastline
Debris erodes both landscape and human structures
Secondary effects
Fires
From ruptured gas lines or other sources
Contaminated water supplies
Floodwaters, wastewater treatment plants, rotting animal carcasses and plants
Disease
Come in contact with polluted water or soil

22. 4.3 Effects of Tsunamis and Linkages with Other Natural Hazards, cont.
Causes of Tsunamis
Earthquakes
Landslides
Volcanic explosions
Asteroids
Caused by Tsunami
Coastline erosion

23. 4.4 Natural Service Functions of Tsunamis
Not many natural service functions, but
May bring nutrients and sediments from the ocean that are needed by soil
May bring in sediment needed to build shoreline
Studying the 2004 Indonesian tsunami may reveal others

24. 4.5 Human Interaction with Tsunamis
Humans cannot prevent or control tsunamis
Human activity does not affect frequency or magnitude
Increased use of shoreline increases consequences

25. 4.6 Minimizing the Tsunami Hazard
A number of strategies for minimizing tsunami hazard
Detection and warning
Structural Control
Tsunami runup maps
Land use
Probability analysis
Education
Tsunami-ready status

26. Detection and Warning Tsunami warning system
Seismographs to detect earthquakes
Automated tidal gauges to determine sea level changes
Buoy sensors with tsunameter to detect small changes in pressure in ocean
Information is relayed by satellite to give arrival time estimates
Warning sirens are used to warn public

27. Tsunami Warning System

28. Structural Control Building designs Seawalls
Houses and small building unable to withstand even one to two meter waves
Larger structures can be engineered to greatly reduce or minimize destruction
Example: Hawaii has special requirements in tsunami zones
Most areas still do not have adequate codes
Seawalls
Purpose is to not allow tsunami to move inland
How high?
False sense of security

29. Tsunami Runup Maps After a tsunami Before a tsunami
Show levels to which the water did travel
Show variability with topography, location, etc.
Before a tsunami
Area that is likely to be inundated by a given height
Indicate areas that would be most vulnerable
Both types used to plan for possible future events
Can use in conjunction with Land use

30. Tsunami Runup on Oahu, Hawaii

31. Huntington Beach, California, Tsunami Runup Map

32. Land Use Natural vegetation may provide defense
Scientists discovered role of tropical ecology after 2004 Indonesian tsunami
Large waves will still destroy just about everything
Villages that were located behind natural vegetation partly protected from tsunami energy
Development of land must be monitored
Removing the natural vegetation on coasts to develop makes them more vulnerable
Plant or retain natural vegetation
However, still could pose danger with debris

33. Trees Provide Some Protection from Tsunami Damage

34. Probability Analysis Hazard analysis traditionally
Based on past events
Deterministic (runup maps)
Probabilistic approach would provide more information
Steps
Identify potential earthquake sources and their uncertainties
Specify relationships that increase or decrease tsunami waves
Apply probabilistic analysis to the tsunami similar to what is done with earthquakes
Still being developed
Difficult because events in one particular area are rare

35. Education Critical to minimize risk
Educate people on the signs of tsunami
Educate on difference between watch and warning
Tsunami watch: a possible trigger has occurred for a tsunami
Tsunami warning: a tsunami has been detected
Educate on behavior of tsunamis
Series of waves
Returning water just as dangerous as the incoming water

36. Tsunami-Ready Status For a community to be “tsunami-ready”
Establish emergency operation center (24 hs)
Be able to receive tsunami warnings
Have ways to alert the public
Develop a preparedness plan with drills
Promote community awareness program
Educational component is of particular importance
May still not be adequately prepared even if “tsunami-ready”

37. 4.7 Perception and Personal Adjustment to Tsunami Hazard
Many do not know signs of tsunami or what to do in a watch or warning
Actions to take in a warning
If you feel a strong earthquake, leave the beach and low-lying coastal areas immediately.
If the ocean recedes, run from the beach for higher ground.
Do not assume that all locations are safe because of an absence of dangerous waves elsewhere.
The time between waves can be up to an hour. Stay out of dangerous areas until a notice that all is clear is given.

38. 4.7 Perception and Personal Adjustment to Tsunami Hazard, cont.
Actions to take in a warning, cont.
If you hear a siren, move away from the beach to higher ground and listen for emergency information.
If you are aware that a tsunami watch or warning has been issued, do not go down to the beach to watch the tsunami.
If waves are arriving and there is no time to move inland, seek a high and strong building (top floor or rooftop).
If all else fails, climb a tall, strong tree.
If trapped in the water and swept away, look for something to use as a raft.

39. Japan 2011: Tsunami and Nuclear Disaster – Applying the 5 Fundamental Concepts
Japanese people have studied earthquakes and tsunamis for decades
People are well aware of potential earthquake and tsunami hazards
More than 7750 mi of tsunami seawalls protecting about 43 percent of coast
Large magnitude and height of tsunami was surprise
Seawalls not high enough
Underestimated risk because of false sense of security
Small town with high wall survived
Seawalls still delayed inundation

40. Japan 2011: Tsunami and Nuclear Disaster – Applying the 5 Fundamental Concepts, cont.
Fukushima Daiichi nuclear power station was shutdown as planned
Seawalls were not enough to keep large tsunami out
Flooded generators for cooling system
Poor evacuation knowledge/procedures
Told to stay when should have evacuated
Many left in freezing conditions (many elderly)
More deaths from evacuation than tsunami in the area
Incident started discussion about humans compounding hazards

41. Chapter 4 Summary
A tsunami is produced by the sudden vertical displacement of ocean water.
The major source of large damaging tsunamis over the past few millennia has been giant earthquakes associated with the major subduction zones on Earth.
When seafloor earthquakes occur, both distant and local tsunamis may be produced.

42. Chapter 4 Summary, cont.
The largest tsunamis generated by earthquakes are produced at subduction zones.
Effects of a tsunami are both primary and secondary. The primary effects are related to the powerful water from the tsunami runup that results in flooding and erosion. Secondary effects include potential for water pollution, fires in urban areas, and disease to people surviving the event.

43. Chapter 4 Summary, cont.
Tsunamis are linked to other natural hazards. They are obviously tightly linked to the earthquakes that cause them; tsunami waves also interact with coastal processes to change the coastline through erosion and deposition of sediment.
Tsunamis can move sediment and nutrients inland with long-term ecosystem benefits.
Occurrences of tsunamis are not influenced by human activities, but we can take actions to reduce their potential impacts.

44. Chapter 4 Summary, cont.
A number of strategies are available to minimize the tsunami hazard, including detection and warning, structural control, construction of tsunami runup maps, land-use practices, probability analysis, education, and achieving tsunami-ready status.
We can detect distant tsunamis in open ocean and accurately estimate their arrival time to within a few minutes. It is more difficult to provide adequate arrival time for local tsunamis.

45. Chapter 4 Summary, cont.
Without adequate education, watches and warnings are often ineffective because so many people do not know how to recognize a tsunami or take appropriate action to save themselves and others.
Along coasts with great or significant tsunami hazard, most communities have not adequately prepared for this underestimated natural hazard.

46. Chapter 4 Summary, cont.
There are several personal adjustments to minimize your tsunami hazard
Most important is to heed tsunami warnings
Local tsunami may arrive quickly following a tsunami-generating event: leave the beach is you fell a strong earthquake or if the water suddenly withdraws.
Remember that tsunami waves often arrive as a series of waves separated by a variable time period.