December 26, 2004: Indian Ocean Earthquake and Tsunami

One of the worst natural disasters of the 21st century unfolded on

December 26, 2004, following a magnitude 9.0–9.2 earthquake off the

coast of Sumatra in the Indian Ocean. During this catastrophic

earthquake, a segment of the seafloor the size of California suddenly

moved upward and seaward by several tens of feet, releasing more

energy than all the earthquakes on the planet in the last 25 years

combined. The sudden displacement of this volume of undersea

floor displaced huge volumes of water and generated the most

destructive tsunami ever recorded.

Within minutes of the earthquake, a mountain of water more

than 100 feet high was ravaging northern Sumatra, sweeping into

coastal villages and resort communities with a fury that crushed all

in its path, removing buildings and vegetation, and eroding shoreline

areas down to bedrock. Similar scenes of destruction and devastation

rapidly moved up the coast of nearby Indonesia, where residents

and tourists were enjoying a holiday weekend. In some cases,

the sea retreated to unprecedented low levels before the waves

struck, drawing people to the shore to investigate the phenomena—

in other cases, the sea waves simply came crashing inland without

warning. Buildings, vehicles, trees, boats, and other debris were

washed along with the ocean waters, forming projectiles that

smashed at speeds of up to 30 miles per hour into other structures,

leveling all in its path, killing approximately 300,000 people.

The displaced water formed a deepwater tsunami that moved

at speeds of 500 miles per hour across the Indian Ocean, smashing

within an hour into Sri Lanka and India, wiping away entire fishing

communities and causing widespread destruction of the shore environment.

South of India are many small islands, including the Maldives,

Chagos, and Seychelles, many with maximum elevations only

tens of feet above sea level. As the tsunami approached these

islands, many wildlife species and tribal residents fled to the deep forest,

perhaps sensing the danger as the sea retreated and the ground

trembled with the approaching wall of water. As the tsunami heights

were higher than many of the maximum elevations of some of these

islands, the forest was able to protect and save many lives in places

where the tsunami rose with less force than in places where the

shoreline geometry caused large breaking waves to crash ashore.

Several hours later the tsunami reached the shores of Africa

and Madagascar, and though distance diminished its height to less

than 10 feet, several hundred people were killed by the waves and

high water. Kenya and Somalia were hit severely, with harbors

experiencing rapid and unpredictable rises and falls in sea level,

and many boats and people washed to sea.

The tsunami traveled around the world, being measured as

minor (inches) changes in sea level more than 24 hours later in the

North Atlantic and Pacific. Overall, more than 300,000 people perished

in the December 26th Indian Ocean tsunami, though many

could have been saved, if a tsunami warning system had been in

place in the Indian Ocean. Tsunami warning systems are capable of

saving lives by alerting residents of coastal areas that a tsunami is

approaching their location. These systems are most effective for

areas located more than 500 miles (750 km), or one hour away from

the source region of the tsunami, but may also prove effective at

saving lives in areas closer to a tsunami. The National Oceanographic

and Atmospheric Administration operates the Pacific

Tsunami Warning Center in Honolulu, Hawaii, integrating data from

several different sources, including seismic stations that record

earthquakes and quickly sort out those earthquakes that are likely to

be tsunamogenic. A series of tidal gauges placed around the Pacific

monitors the passage of any tsunamis past their location, and if

these stations detect a tsunami, warnings are quickly issued for

local and regional areas likely to be affected. Analyzing all of this

information takes time, however, so this Pacific-wide system is most

effective for areas located far from the earthquake source.

Tsunami warning systems designed for shorter-term local

warnings are also in place in many communities, including Japan,

Alaska, Hawaii, and some Pacific islands. These warnings are

based mainly on estimating the magnitude of nearby earthquakes

and on the ability of public authorities to rapidly issue warnings so

that the population has time to respond. For local earthquakes, the

time between the shock event and the tsunami hitting the shoreline

may be only a few minutes. So if you are in a coastal area and feel a

strong earthquake, you should take that as a natural warning that a

tsunami may be imminent and leave low-lying coastal areas.

U.S. scientists detected the magnitude of the Sumatra earthquake

and tried to warn countries in soon-to-be-affected regions

that a tsunami might be approaching. However, despite efforts by

some scientists over the past few years, no systematic warning system

was in place in the Indian Ocean. Initial cost estimates for a

crude system were about $20 million, deemed too expensive by poor

nations that needed funds for more obviously pressing humanitarian

causes. When the earthquake struck on a Sunday, scientists who

tried contacting countries and communities surrounding the Indian

Ocean to warn them of the impending disaster typically found no

one in the office and no systematic list of phone numbers of emergency

response personnel. Having such a simple phone-pyramid list

could potentially have saved tens of thousands of lives. Indian

Ocean communities are now planning to establish a tsunami warning

system before the next tsunami strikes.

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