The Mentawai island chain, an underdeveloped region of Indonesia, was closest to the magnitude 7.7 undersea earthquake that struck at the Sunda megathrust fault and caused a large tsunami during the evening hour of 9:42PM on October 25.
Local reports described the disaster. The sea water receded far away, and when it returned, a ten foot wall of water rushed in and ripped out trees, houses and all things in its way. The tsunami receded and sucked everything out to sea, leaving almost nothing behind.
The death toll from the tsunami is now up to 370 while 300 are still missing, probably swept out to sea.
Following the devastating December 26, 2004 magnitude 9.3 earthquake just off the coast of Sumatra, Indonesia which produced one of the deadliest natural disasters in recorded history (a tsunami that killed 226,000 people), an early warning system was built in the region to warn of future tsunamis.
However, after the recent Mentawai tsunami, there have been reports of partial failure of the new early warning system due to maintenance issues with offshore buoys, while at the same time some populated areas did apparently receive warning messaging by text, radio, and sirens. The scope of providing early warning to such a vast coastline including large numbers of remote villages without cell phone, wireless, or radio, is tremendous at best.
Update, 31-Oct-2010, the tsunami death toll has climbed to 449 with more still missing.
Just 20 hours later during October 26 at 6PM, about 750 miles away the Mt Merapi volcano erupted into an explosion of gas and ash, killing 33 people. The volcanic eruption occurred on the worlds most heavily populated island of Java, Indonesia (136 million) which contains 60 percent of the entire population of Indonesia.
The Mt Merapi volcano’s deadliest eruption occurred during 1930 when more than 1,300 people were killed. Another eruption during 1994 killed more than 60 people.
Update, 31-Oct-2010, Mt Merapi has erupted several times since it began last week and has claimed 38 lives. Farms have been destroyed and covered with ash. The volcanic activity seems to be increasing, according to one local official who is monitoring the volcano.
Update, 14-Nov-2010, the death toll from the Merapi volcano has increased to 250 as the volcano continues periods of eruption while 350,000 people have evacuated the immediate area.
Indonesia is one of the world’s most disaster-prone countries due to its location straddling major tectonic plate boundaries part of the “pacific ring of fire”, where the Indian – Australian plate is diving underneath the Sunda plate. The entire region is very active with many numerous earthquakes and more than 150 volcanoes.
Geologists are currently forecasting a major 8.8 magnitude earthquake in the same region as the 25-Oct earthquake (which reportedly did nothing to relieve stress). They do not know if it will occur during the next 30 minutes or the next 30 years.
One thing for sure, there will be more tsunamis.
There are many thrust fault (up-down slip rather than side-to-side slip) regions in the world located offshore from major population centers that present hidden tsunami risk.
One in particular that comes to mind is the Cascadia subduction zone in the Pacific Northwest of the USA stretching from Vancouver to northern California. The zone is capable of producing very large megathrust earthquakes of magnitude 9 or greater, if the entire zone ruptures. Not only could a large earthquake decimate much of the northwest USA, but the threat is there for a great tsunami from the effects of rapid uplift or sudden drop at the sea floor.
Some reports suggest that geologists have determined in recent studies that there is as much as a 37 percent chance that the Cascadia subduction zone will produce a colossal magnitude 9 or higher earthquake within the next 50 years and produce a tsunami as high as 100 feet.
One wonders how many are aware of this, or are even prepared for survival of such an event in regions where it is rather uncommon to experience these things, while the danger exists right under their feet.
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