Wave files

For anyone not affected by the Indonesian tsunami, memory of the catastrophe has begun to fade. Nevertheless, a year later, it's worth remembering the tragedy and asking what's being done to save people from future killer waves. The tsunami of December 26, 2004--triggered by one of the largest earthquakes recorded since 1900--spread outward at nearly 500 miles per hour, leaving nearly 300,000 people dead across the Indian Ocean.

Space-borne cameras recorded the destruction in remarkable detail. Go to DigitalGlobe (www.digitalglobe. com/tsunami_gallery.html) for before-and-after images of coastland that turned brown as the waters swept them clean of vegetation. Scroll down to the images of Kalutara, in Sri Lanka, where swirling floodwaters surged in violent retreat from the beaches. The Center for Remote Imaging, Sensing and Processing at the National University of Singapore has more satellite images (www.crisp. nus.edu.sg/tsunami/tsunami.html). Another site at NASA has Landsat 7 images of the hard-hit Sumatran coast, where monster waves plowed inland for a mile or more (www.nasa.gov/ vision/earth/lookingatearth/Landsat_Tsunami.html). A variety of sites inventoried at serc.carleton.edu/NAGTWork shops/visualization/collections/tsunami_other.html give a feel for how the waves propagated through the ocean. Click on "Tsunami Visualization Collection" in the box near the top for an array of animations that show how the catastrophe unfolded. For example, scroll down to "Tsunami Generation" near the bottom for a QuickTime video showing how slippage in the Earth's crust can lift huge volumes of water to form the destructive waves.

By chance, the Indonesian event was the first major tsunami detected from space as it took place. Unfortunately, it's not practical to rely on satellites to detect tsunamis, primarily because a huge orbiting fleet would be needed for appropriate coverage. Future systems are more likely to deploy an array of pressure sensors on the ocean bottom, which have already proved capable of detecting tsunami waves only half an inch high.

For an animation of that kind of system, go to NOAA's Deep-ocean Assessment and Reporting of Tsunamis (DART) page (www.pmel.noaa. gov/tsunami/Dart/dart_ms1.html), or go to www.ndbc.noaa.gov/Dact/dart_map. shtml for a snap of the U.S. system that has been operating in the Pacific since late 2003. The new Indian Ocean warning system, scheduled to become operational this year, is described in National Defense magazine (www. nationaldefensemagazine.org/issues/2005/ Nov/Indian_Ocean.htm).

A page on the National Academy of Engineering's site (www.nae.edu/ nae/bridgecom.nsf/weblinks/MKEZ-6DJ KL9?OpenDocument) presents five articles by tsunami experts on what they've learned from the Sumatra wave and prospects for better warning systems. At tsunamilessons.blogspot. com citizen Doug Carlson keeps close track of what the U.S. government is doing to ensure early notification, particularly near his home in Honolulu. And Atlantic-coast dwellers shouldn't be complacent either. Go to Steven N. Ward's site (es.ucsc.edu/ward/) and click on "Computer Simulations." Ward, a geophysicist at the University of California, Santa Cruz, has posted animated movies of waves caused by historic and hypothetical landslides and asteroid impacts, some affecting the East Coast. Under the "Impact Tsunami Simulation Movies" menu, select the movie of the Chicxulub event, and you'll see the behemoth wave that accompanied the end of the age of dinosaurs.

ROBERT ANDERSON is a freelance science writer living in Los Angeles.

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