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.

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.

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

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

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

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

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

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

Tsunami

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

Distant and Local Tsunamis

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

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

Global Tsunami Hazard

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

2004 Tsunami Killed People on Both Sides of Indian Ocean

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

Tourists Running for Their Lives

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

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

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

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

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

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

Tsunami Warning System

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

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

Tsunami Runup on Oahu, Hawaii

Huntington Beach, California, Tsunami Runup Map

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

Trees Provide Some Protection from Tsunami Damage

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

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

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”

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.

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.

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

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

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.

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.

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.

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.

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.

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.