The high-resolution images in this Envirocast® Bulletin were captured by Space Imaging's IKONOS satellite. They show the northwestern tip of Sumatra (Indonesia) before and after the moment of tsunami impact. Image processed by StormCenter Communications, Inc.

New:  Envirocast Special Edition -- South Asia Tsunami

NOTE: Credit to Space Imaging / CRISP - Singapore must appear on-screen throughout the entire air-time.
 

Before and After the Tsunami - Aceh, NW Sumatra, Indonesia

• The world's biggest earthquake in 40 years hit southern Asia on December 26, 2004, unleashing a tsunami that crashed into eight countries around the Indian Ocean.
   

• Just before the killer waves struck, sea level fell rapidly, appearing like an extreme low tide and exposing the seafloor - one of the definite warning signs of an approaching tsunami.  Then water surges onshore and powerful currents sweep everything back out to sea.
   

• 'After' imagery show the effects of the water surging onshore and the powerful currents sweeping everything back out to sea.
   

• StormCenter's Earth and Oceans expert, Dr. Ellen Prager describes the tsunami as follows:
  
  "Tsunamis can be highly variable in the way they strike, some coasts may have been struck by a towering wall of water while others may have experienced a tremendous surge of water. Much of this variability depends on the configuration of the coastline and changes in bathymetry as the waves approach. The destruction from the tsunamis comes from the onslaught of the water, the power of the waves and surge, and then the swiftly flowing currents as the water returns to the sea.
  
  If you live or visit the coast and you feel the earth shaking, see the ocean's level lower rapidly, or hear a loud rushing noise or bang from offshore, your immediate reaction should be to run inland and up as far as possible. Do not go to the shore to investigate and if a warning is issued, take heed and go to a safe location inland preferably on higher ground."

• A tsunami (pronounced soo-nahm'ee) is a series of waves generated by the sudden movement or disturbance of the seafloor. Tsunamis are fast-moving, low, long waves that radiate out from a triggering event, such as an undersea earthquake, volcanic eruption, landslide or asteroid impact.  Once one of these waves reaches shallow water, they change…becoming towering, powerful walls of water that slam ashore. 

Hypothetical Tsunami along the Pacific Northwest Coast (QuickTime 2.2Mb)

• Tsunamis or seismic sea waves differ markedly from typical waves generated by the wind.  Imagine blowing over the surface of a coffee cup…the top surface of the liquid inside moves in small waves.  Now shake the cup and all the water sloshes back and forth and over the lip – this is a tsunami.  In wind waves only a relatively small portion of the water is in motion…near the surface.  In contrast in a tsunami the entire water column, from the surface to the sea floor, begins to move and transfer energy.

• Although tsunamis travel as low, very fast waves, often over 500 mph, once they reach shallow water, they slow down and bunch up.  It is here that the true danger lay.  Sometimes the water along the beach will recede right before a tsunami hits.  Seconds later, one or more towering walls of water will crash ashore.  And not only is the direct hit of the waves extremely dangerous, but also the currents created as the water piled onshore swiftly flows back out to sea.

• Tsunami’s occur most commonly in Indonesia and other coastal regions around the Pacific where triggering events are more likely due to the region’s seismic activity.