Indonesia Tsunami – News update and explanation

South-East Asia was recently the victim of yet another natural disaster in the form of a tsunami that has so far claimed the lives of at least 435 with another 100 thought to be missing.

More than 23,000 people have been displaced by the tsunami in a region where in the shadow of Mt Merapi, central Java, people are only just returning to their villages to check if homes and farms are still there following volcanic activity that killed 36 people last week.

Many homes were destroyed by waves after the 7.7 magnitude quake, which struck 20km (13 miles) under the ocean floor near the Mentawai islands. Ten villages on the islands were completely swept away by the  tsunami reported to have been between3-6 metres high.

Map

The epicentre of the earthquake was just off the coast of Sumatra, Indonesia (Picture: BBC)

The vast Indonesian archipelago sits on the Pacific Ring of Fire, one of the world’s most active areas for earthquakes and volcanoes due to the movement and collision of tectonic plates. In the recent past more than 1,000 people were killed by an earthquake off Sumatra in September 2009, while in December 2004, a 9.1-magnitude quake off the coast of Aceh triggered a tsunami, now know as the boxing day tsunami, in the Indian Ocean that killed a quarter of a million people in 13 countries including Indonesia, Sri Lanka, India and Thailand.

What Causes Tsunamis

Tsunamis,  also incorrectly known as tidal waves, can be caused by several mechanisms that cause the displacement of water which then form waves which are so devastating when they reach land fall. Major tsunamis are often caused a large earthquake at sea which causes the seabed to move vertically displacing the water and causing waves to move away from the epicentre. The other mechanisms are submarine landslides and cosmic impacts i.e. meteors.

In deep water, the tsunami moves at great speeds and have been recorded up to 500mph. When it reaches shallow water near coastal areas, the tsunami slows but increases in height causing the wall of water that observers describe.

 

Graphic showing how the the large waves that create a tsunami are formed by the upward movement of the Earths under-sea plates after a sub-oceanic earthquake

Earthquake mechanism for causing tsunamis (Animated guide available via BBC)

As the waves reach land they are at their slowest but also at their highest. A Tsunami is not a single wave but a series of waves, also known as a wave train. The first wave in a tsunami is not necessarily the most destructive. Tsunamis can approach the shore as fast as 100 miles per hour and extend inland up to a thousand feet. They also tend to retreat as quickly and forcefully as they come inland with many victims swept out to sea as the waters subside.

The Tsunami Warning System (TWS) in operates in the Pacific and is comprised of 26 member countries with seismological monitors and tidal stations throughout the Pacific region. The system evaluates potentially tsunamigenic earthquakes and issues tsunami warnings

 

This isn’t a tsunami but its pretty rad

Further Reading:


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