Indonesian Tsunami

  ella33 17:43 27 Oct 10
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Very sad news of course, for everyone involved and we are particularly aware of the horror and devastation as the Boxing Day tsunami of 2004, still seems like only yesterday.

The sad situation does raise certain questions and I wondered if anyone here is acquainted with the area and the earthquake epicentres affecting the sea. After the 2004 tsunami there was much public debate about warning systems and why they didn't have any. Whether the countries affected are too poor, or whatever other reason.

click here

This link suggests that there were warning systems in the Indonesian Islands but they had been vandalised. Another argument suggests that the islands were so close to the epicentre of the earthquake, that they couldn't have raised the alarm soon enough anyway.

There is also the argument that if the warning systems do work effectively, then the quake is so far out in the ocean that by the time the waves reach the land, they are no longer a threat.

I don't know the area but I am interested to know whether people here know whether there is an effective warning system against a tsunami?

  Forum Editor 18:37 27 Oct 10

but I've visited Padang, the Indonesian port that's a couple of hundred kilometres away on Sumatra.

There is a Tsunami warning system in the area, it consists of wave monitoring buoys moored at sea, and I know there's been a problem with local fishermen stripping out anything electronic that looks worthwhile. I'm not suggesting that's the reason the system didn't operate, but it's a distinct possibility.

The other possibility is that the buoys were transmitting, but because the earthquake epicentre was so close to the islands the tsunami hit before the people on the islands could be alerted - the water rolled over the islands ten minutes after the quake.

  morddwyd 19:57 27 Oct 10

And now they have a volcano to cope with as well

click here

  ella33 20:15 27 Oct 10

Morddywd: And the possiblity of more eruptions from Mount Merapi, so I certainly wish them all the luck they can get.

FE thank you for your information, I hadn't heard about the fishing vessels, but I had heard that it was unlikely that the islanders could have been warned in time.

At least the emergency services such as Red Cross have been able to help on this occasion. It is often sad to hear of countries who will not allow them in.

I heard one story from the 2004 tsunami: a European child who had learned about tsunami as part of her world geography lessons, saw that the beach was suddenly dry and alerted her parents that she had learned this could mean a tsunami was very near. Her parents told people on the beach and hundreds fled and were saved. I had heard a couple of similar stories about the dry beach before and people "in the know" alerting others to the danger and telling them to run. I wonder if there was any natural warning on the Mentawai Islands. I guess what I am thinking is, I wonder why the world doesn't know more in 2010!

  Forum Editor 23:50 27 Oct 10

the sea can recede from the beach, and as it does so it often has a characteristic foamy look right at the edge of the water. Sometimes the water recedes quite slowly, at other times it can surge out.

The best warning of a possible Tsunami is the quake itself - if you're on a beach and you feel an earth tremor, head for higher ground as fast as you can.

Tsunamis travel through the sea at enormous speeds, sometimes in excess of 500mph, but if you're out on the water you'll see nothing - the Tsunami pressure wave races across the ocean without raising a wave. The wave is generated as the Tsunami reaches shallow water, and the drag exerted by the shore slows the lower part. The upper part of the wave isn't slowed, so it tries to overtake the lower part, rising as it does so. This is what causes the notorious Tsunami wave that can be so damaging.

I once experienced a mini Tsunami wave on a beach in Thailand - it was only about a metre high, but it was fast, and knocked me over. It was only later that I learned it had been a Tsunami wave caused by a minor undersea quake.

  ella33 10:23 28 Oct 10

FE that is interesting, I didn't know that boats just sailed over and the giant waves are on the shoreline only. When the news pictures showed a guy who had been watching fom a yacht, he understandably looked shaken and upset because of what he had witnessed but I was surprised then that his boat was safe but now I see why.

I also read that the "plate" that moved, causing the quake, was the same plate as the 2004 tsunami. It didn't seem that close to me but maybe it does to people more aquainted with the area. So it would appear the general area is a kind of black spot for under seabed quakes.

  Forum Editor 19:27 28 Oct 10

the best thing to do is put to sea, and get as far from shore as possible. You'll probably not even notice the energy wave as it passes beneath you.

The quake that caused the Indonesian Tsunami was almost certainly an aftershock following an earlier, more powerful event. There have been several powerful quakes in the region over the past few years, and they're all related to the same plate boundary.

Indonesia is sitting on the Sunda tectonic plate and that is in collision with the Australian plate. The Australian plate is diving under the Sunda plate in what's called the Sunda trench, and it's moving at the rate of around two and a half inches a year. In Plate tectonic terms that's fast, and monumental stresses occur. Something has to give, and when the plates suddenly jerk under pressure the result is an earthquake. The Northern end of the trench is off the coast of Sumatra, and it was there that the 2004 Tsunami was started - there was a 9.1 scale earthquake, and that's absolutely enormous in earthquake terms.

When earthquakes happen under the sea there can be huge movements of the sea bed as it's thrust upward, and the result is often a Tsunami.

These plate boundaries are the most geologically active areas in the world, so your description of the area as an earthquake 'black spot'is right on the money.

  ella33 22:19 28 Oct 10

It is amazing that so much is known about earthquakes, especially in that area but no one can predict them and there is no way of preventing them. Tsunamis can only be predicted after the earthquake but there doesn't seem to be any technology to have any idea when a quake will strike. but I feel sure there are many geologists working on it.

  Forum Editor 22:35 28 Oct 10

working on improving earthquake prediction methods, but there are still no reliable ways to predict where or when an earthquake will occur, or its likely severity.

There are of course well known earthquake zones, and scientists can predict the probability of earthquakes in these areas, but there's no sure way to say that an event will occur even days in advance, let alone longer periods.

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