Tsunamis on the Pacific

Toss a stone into a pond, and ripples move in all directions away from the point of impact.  As they collide with the shore and with one another, they bounce back and interfere, creating turbulence across the water.  These ripples work on the small level of the pond, but also on the larger scale of entire oceans.  The maps of tsunamis created by underwater or coastal earthquakes look surprisingly similar to ripples moving across a pond.

The map above was created by the National Oceanic and Atmospheric Administration (NOAA) Alaska Tsunami Warning Center.  It shows how a tsunami created by an earthquake on the southern Alaskan coast would travel across the Pacific Ocean and beyond.  On this map, each band of color represents an hour of travel time.  A tsunami starting in Alaska could travel the 6,500 miles to Australia in only 15 hours.  Click here or on the picture above to see the large version of the map.

As with the ripples in the pond, any interference with the tsunami wave will cause it to bounce back and interfere with itself.  See, for instance, the Bering Sea in this map.  Although relatively close to the epicenter of the earthquake, the Aleutian Islands and the enclosed nature of the sea itself force resistance upon the waves, slowing it down.  On the contrary, however, the Pacific island nations present few obstacles to the tsunami wave due to their small land size and the large distances of open water between them. 

The presence of the Great Barrier Reef off northeastern Australia adds more than two hours to the tsunami’s travel time in some places.  And the wave slows down considerably across Indonesia’s Arafura and Java Seas.  This map therefor demonstrates the importance of barrier islands in ensuring a safe coastline–not just from tsunamis, but also from high waves caused by hurricanes or other powerful storms.

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Sichuan Province Earthquake

Most of you have probably heard by now about yesterday’s large earthquake registering 7.9 on the Richter Scale in China’s Sichuan province.  As casualty reports continue to mount, several organizations have released maps of the affected areas.  The map above is a “shake map” showing the percieved shaking and potential damage throughout the area of the epicenter.  The star indicates the epicenter of the earthquake.  The scale at the bottom of the map also shows the percieved rate of movement of the ground during the earthquake.  The red area around the epicenter experienced ground moving at over than 3.8 feet per second. 

This map is part of a series available from the U.S. Geological Survey, including population exposure and historical seismicity.  The New York Times has also released an interactive map of the affected area, overlaying photographs, population figures, potential damage, and a couple of the most major incidents.  CNN has also released this more limited interactive map, overlaying a few significant events and statistics over a broader map of China.

Coming on the heels of Cyclone Nargis in Burma, this is a second major tragedy for Asia in less than two weeks.

Burma and Cyclone Nargis

With the death toll in Burma of Cyclone Nargis climbing to 10,000 and above, humanitarian groups have begun to release maps of the affected areas.  Some of the most interesting and detailed maps I’ve seen have been produced by UNOSAT–the UN Institute for Training and Research Operational Satellite Applications Program.  UNOSAT is jointly administered by the United Nations and the European Organization of High Energy Physics (CERN).  UNOSAT develops and delivers its maps in support of humanitarian efforts, peace, and international development and security. 

UNOSAT’s has released several maps of the impact of Cyclone Nargis on Burma’s coastal regions, some of which are available here, including maps of the Yangon (Rangoon) area, the Laputto and Bagale townships, and the delta of the Ayeyarwady River, which are among the hardest hit parts of the country.  The maps overlay terrain, urban areas, roads, and other infrastructure with satellite-detected flooding.  The path of the cyclone, including its category and wind speeds, is also tracked on the map.  Finally, the maps include tables of estimated flood areas in several of the larger cities.

These maps demonstrate one of the reasons for the substantial death toll–the cyclone’s path was directly over some of Burma’s most heavily populated areas.  The capital city of Rangoon took a direct hit from the eye of the cyclone.  The extent of the storm surge, and the depths of water indicated in the tables, suggest large numbers of casualties from flooding in addition to the high winds.

UNICEF is responding to the humanitarian crisis unfolding in Burma as a result of the cyclone.  You can support their efforts by donating online at this website.

Update: Burma state media is now reporting that the death toll is at 22,000, with 41,000 missing.

Update 2: The New York Times just released this interesting graphic of the overall damage.