Coastal Catastrophes: Tsunamis

Long-Wavelength Waves: Tsunamis or Harbor Waves.

Among the most devastating coastal catastrophes are tsunamis or harbor waves. Although they are very infrequent, when they do occur, they can travel large distances across ocean basins and result in significant destruction and loss of life. The four projection maps shown in Figure 5.29, show the areas of the globe that are most prone to tsunami generation (i.e., shown in red highlights). Most of these areas are identified as high risk for generating tusnamis because, not only are they plate boundary areas, they are also associated with subduction zones where two tectonic plates collide and one is pushed below another. These maps and information about simulating tsunami events for predicting their travel and impacts are from NOAA's Center for Tsunami Research.

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Figure 5.29: Projection maps showing the areas where most tsunamis originate.

Credit: These are maps produced by NOAA's Center for Tsunami Research.

For those interested in a sobering article, it would be good to check out this web article (USGS Circular 1187) titled: Surviving a Tsunami—Lessons from Chile, Hawaii, and Japan. The link provides some important details about tsunamis and some critical information items on how to survive an event, if you are ever faced with the need to do so.

Unfortunately, tsunamis and the earthquakes that produce them are not readily predicted, although some regions are more prone to their occurrence than others. NOAA and its research partners are working and collaborating on ways to detect these events and as needed are working on strategies to notify people around the world of a tsunami event should one be detected. A variety of tools are used today by geoscientists to help detect these phenomena and as much as possible to warn residents and coastal communities of their potential occurrence. We will learn later in the module about tools and the data they collect. However, detecting tsunamis was not always possible, and we still have limitations. Historically, tsunamis have produced incredible numbers of deaths. In some cases, single events have been responsible for the loss of 100,000 or more people at a time.

Detecting Tsunamis: The Pacific Tsunami Warning Center
Today, in partnership with the USGS and NOAA, the Pacific Tsunami Warning Center (PTWC) operates from Hawaii. The warning center was first created after WWII as a result of the 1946 Aleutian Island tsunami that originated between Alaska and Siberia. The tsunami produced incredibly destructive waves that traveled hundreds of miles to the south and resulted in severe inundation of Hilo Bay, Hawaii and led to numerous deaths. Formerly initiated in 1949, the center expanded in the aftermath of the 1960 Chilean earthquake that not only destroyed many communities along the coast of Chile, but also led to more destruction in Hawaii and even in Japan on the opposite side of the Pacific Ocean. With such severe long-distance impacts, it was clear that individual nations needed to collaborate in order to effectively save lives. As a result, efforts were initiated to coordinate monitoring around the Pacific, but even in 2004 the effectiveness of the center was limited as demonstrated by the 2004 Sumatran Tsunami that impacted much of the Indian Ocean. Although the earthquake and tsunami were detected from the Pacific, little could be done to monitor its progression in the Indian Ocean and efforts were more or less futile in terms of issuing effective warnings to residents living around the Indian Ocean basin. As a result of that event, the center now coordinates with other tsunami warning centers in the U.S. (including the West Coast and Alaska Tsunami Warning Centers) and with the United Nations and similar agencies in several other countries including Japan, Australia, and others. These centers not only detect earthquake activity, but also track development and movement of tsunami waves as they travel across the world's oceans. The main missions of these centers are to monitor and issue warnings, advisories, and watches to help reduce the loss of life associated with these events around the world.

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Figure 5.30: USGS Photo from 1960 Onagawa Japan when tsunami waves from the Chilean earthquake inundated coastal areas on the entirely opposite side of the Pacific Ocean. Waves came ashore some 20 hours after the actual earthquake.

Credit: USGS: Circular 1187

The PTWC's websiteis a great resource that provides details about specific events around the globe that are being monitored for tsunami generation. A similar interface is also found at the West Coast Alaskan Tsunami Warning Center as well. Australia and a few other countries maintain similar websites. It is worth spending a little bit of time exploring the types of tools and data that these agencies are collecting and monitoring to help keep the public as safe as possible from these types of catastrophes. It is, however, up to individuals and communities to be educated about tsunami risk and hazards and to act on the information provided in order to save lives. Individual communities are ultimately responsible for developing evacuation plans and limiting shoreline development in especially susceptible areas. These topics will be explored in greater detail in later modules.

So, yes, it's clear that tsunamis pose an incredible threat to coastlines and societies around the world; but exactly what are tsunamis, how are they formed, and how do they interact with coastlines around the world? In order to answer these questions, we will explore two case studies. The first is the Sumatran Tsunami that occurred in December of 2004, and the second is the 2011 Japanese Tsunami that devastated the island of Honshu, one of Japan's main islands.

• Investigating The Geology & Impacts of Recent Tsunamis
• Tsunami Summary