Coastal communities are at risk from the same effects earthquakes have on inland population centers and have the additional peril of coping with tsunami events caused by a significant earthquake. The sudden uplifting or movement of a large parcel of water generates tsunamis. Tsunamis are defined by the two different mechanisms that create one of these severe wave events. These are distant source and locally generated tsunamis.
Distant Source Tsunami – The sudden shifting of the seabed caused by an earthquake generates the first type of tsunami. Rapid movement of tectonic plates pushes a large volume of water quickly upward. Waves generated by one of these disturbances are almost imperceptible in the open ocean, a substantial wave may only be inches tall in deep water. Tsunamis aren’t a single wave event, but are actually composed of a series or train of waves. These waves are characterized by their long periods, the length from peak to peak of each wave.
Tsunami waves generated in the open ocean are characterized by long periods between wave crests. The height of the wave in deep water may only be a few inches. The waves can reach speeds up to 600 miles per hour. These tsunami waves will, however, slow and gain height as they reach shallow waters. A distant source tsunami is defined as being generated at least 600 miles from its point of impact. Wave trains move at more than 500 miles per hour. Wave heights do not build until the wave reaches more shallow, near-shore water. Tsunami generated at a distance can be tracked, and due to their constant speed, accurate predictions and warnings can be made for the onshore arrival.
Locally Generated Tsunami – Severe waves can be generated by cataclysmic events that displace large parcels of water. An immense submarine landslide triggered by Alaska’s Good Friday Earthquake in 1964 destroyed the waterfront of Valdez and killed a number of people. An event like this offers little or no warning to people living along the coast. Other events besides earthquakes that displace water can cause a tsunami. These can be things like a meteor strike, nuclear explosion or volcanic eruption.
A less common form of wave, generated by an earthquake, is termed a seiche. It is characterized as an oscillation or sloshing of water within an enclosed body of water. It’s a bit like the water bouncing back and forth in a bathtub. The wave that destroyed much of Valdez likely had elements of seiche associated with it. The phenomenon has been observed in the Great Lakes of the United States.
Tsunami Hazard Characterization – The direct damage caused by a tsunami can be characterized in three different ways and disaster planning needs to account for these factors:
- Inundation – This is the degree to which the water from a wave event covers the uplands of a community. Inundation heights are affected by local bathymetry and topography. Terrain features and elevations can heighten flood levels caused by one of these waves. Inundation damages anything harmed by contact with water.
- Wave Action – This is the physical damage caused by the weight and speed of a wave striking an object or topographic feature. Water is comparatively dense and moving water imparts great amounts of energy on objects that it encounters. Structures and objects in the path of a wave are damaged and objects displaced by the wave become projectiles that cause further damage.
- Coastal Erosion – Erosion is an environmental impact of a tsunami event. Moving water and the impact of waves erode soils found along the coast. The damage has a direct effect on local ecosystems, destroying wildlife habitat and causing sedimentation of the water column. Erosion can undercut the foundations of the waterfront structures like fuel tanks whose collapse would further harm the coastal environment.
The deadly Indian Ocean tsunami highlighted the death and destruction to infrastructure that can be caused by one of these wave events. Communities often must deal with the damage caused directly by an earthquake and then brace for the follow-on wave generated by the earth’s movement. The federal government has recognized the need to bolster detection of approaching waves. Local governments along the coast have a responsibility to plan for one these waves and take advantage of warning systems that have been put into place.
Emergency Response Planning for a Tsunami
There are many things that a coastal community can do to prepare for a tsunami and lessen the impact from one of these events on people’s safety and destruction of property. Planning priorities can be broken into areas of warning communications, community preparedness, and administration.
Warning Communications – Any person located within the inundation zone of tsunami is at risk from its moving water and wave impact. Communities planning to effectively respond to a looming tsunami need a way to communicate the pending hazard and mitigation strategies to area residents. Among the planning efforts required for this action item, there needs to be a centralized point of contact establish between local public safety officials and the National Weather Service (NWS) that allows reception of applicable tsunami warnings. This “warning point” needs to be monitored around the clock and there should preferably be a backup method of communication established for use by the warning point.
A means of communicating with the greater community needs to be established. It could include sponsorship of NOAA/NWS weather radio broadcasts, support given to local broadcast radio stations and backing of amateur radio operators. Along with good communications, a site needs to be established where local emergency responders can meet and coordinate their efforts. Known as an emergency operations center (EOC), this facility is key to the effective use of the Incident Command System (ICS) within a community.
Community Preparedness – Preparedness depends on a number of things being established and planned for in advance. It’s too late to identify an evacuation center once a tsunami warning is given. Communities can prepare for a tsunami by promoting awareness programs, establishing shelter locations and stocking them, supporting efforts to develop local inundation maps and use them to craft evacuation routes and maps, provide written information about local plans to the public and encourage educational programs be presented in local schools and at civic functions.
Administration – Effective tsunami planning depends on having an established administrative structure in place that ensures effective plans are developed, tested and promulgated throughout the community. The tsunami disaster plan needs to be tested and exercised yearly among emergency responders and community stakeholders.
Specific Planning Action Items
There are several specific actions that should be pursued by a community to prepare for a tsunami event. These include development of a local emergency action or operations plan (EOP), development of inundation maps and providing community training opportunities.
Emergency Action/Operations Plan (EOP) – Planners needs to determine what areas would be inundated by a tsunami wave. Areas below a hundred foot elevation or within a mile of shore should be included in evacuation plans. Local bathymetry and topographic features will affect flooding. The plan should address the type of tsunami that would pose the greatest risk to the community. This is likely going to be a locally generated/seiche event because of the sever potential for damage and lack of warning. Local history may modify priorities for the worst case scenario. A community like Crescent City, California may consider distant generated tsunami a greater hazard because of past occurrences and geographic location.
The EOP needs to account for threat levels and then conduct an analysis of the vulnerability, risk and consequences of a wave strike. Initial planning should look at areas less than a hundred feet in elevation or within a mile of shore. Once a inundation map is established, this impact area can be better refined. The EOP needs to detail how communications will be conducted after a tsunami warning is received, how are people warned of the pending event and detail how emergency responders talk to each other.
Inundation Mapping – Of all the United States, Alaska has the greatest risk of experiencing an earthquake and associated tsunami. The Geophysical Institute of the University of Alaska Fairbanks and the State of Alaska Division of Geological and Geophysical Surveys are actively mapping the potential inundation of communities that could be caused by a tsunami. Using local bathymetric and topographic data with computer modeling, the inundation maps give local emergency planners an effective tool for establishing evacuation routes and shelter locations. Communities can support this effort by encouraging the Legislature to continue its financial support of the mapping work.
Community Training Opportunities – Community leaders should encourage and sponsor training opportunities to bolster local preparedness. These efforts will benefit effective response to tsunami events and provide skills greatly applicable to any natural disaster experience by a community. Training is available for free or at reduced cost from many different agencies.
American Red Cross – The Red Cross offers well known classes in first-aid, CPR and AED use. They also offer courses aimed at training emergency responders in establishing and operating community shelters.
FEMA – The Federal Emergency Management Agency offers many courses in the use of the Incident Command System (ICS). This system establishs a structure that allows multiple and varied organizations to use a common language and command structure which allows personnel from diverse organizations to work effectively together. ICS is scalable and its management structure can be adapted to a broad range of public emergency situations. Classes are available online and through many different federal, state and local agencies.
A tsunami event of any consequence is likely to involve a response from all available agencies that are present in a community. Most Alaska communities should have local responders keyed into an established operations plan and will see a robust response from the Coast Guard. Other agencies may eventually become involved, but it is important to realize that help may not be immediately forthcoming. Disasters can affect a number of communities and transportation in Alaska is easily disrupted.
Recommendations for Community Response to a Tsunami Event
Seek Designation as a TsunamiReady Community – The National Oceanic and Atmospheric Administration through its National Weather Service has a comprehensive readiness certification program available for use by coastal communities. Communities certified as TsunamiReady have taken significant steps to deal with the impact of a tsunami inundation.
Promote Public Awareness – Locally generated tsunami pose the greatest risk to life and property. These events offer little warning to their potential victims. Encourage people to learn about the key warning signs of an impending wave. Immediately go to higher ground if you experience:
- An extreme change in the tide
- A loud roaring noise
- A strongly felt earthquake, lasting more than 20 seconds, where it is difficult to stand
Secure Local Inundation Mapping – Alaska communities are on a prioritized list for establishment of inundation mapping. These maps are vital to effective planning through identification of evacuation routes, establishment of shelter sites and prepositioning of emergency equipment.
Establish and Practice Using an Emergency Operations Plan (EOP) – Responders will not act effectively during an emergency without adequate preplanning. Establishing an operations plan for dealing with a tsunami allows emergency responders and local residents a chance to better anticipate the actions that need to be taken during a tsunami.
Public service agencies need to be aware of the established plan and practice using it. The first time agency representatives meet each other shouldn’t occur after something bad has already happened. Practicing the plan identifies flaws and other potential players that should be involved.
Sponsor Training Opportunities for Community Residents – Many different agencies offer emergency preparedness training courses that would better prepare a community during a tsunami or other natural disaster. Classes are often available just for the asking. Some minimal support should be made by providing per diem or travel costs for trainers. Training providers include the American Red Cross, the State Fire Marshall, Coast Guard, State Office of Emergency Services and Department of Health and Human Services.
Copyright © 2013 by Alan Sorum