Tsunamis are caused by major earthquakes out to sea. This happened in places where tectonic plates crashed together.

 

 

 

Tsunamis tend to occur at subduction zones and we can see subduction zones rimming the Pacific Ocean. We have the Cascadia subduction zone here, Middle America Trench down here and of course the Peru-Chile Trench down here, which generated the largest subductions on earthquake ever recorded in 1960. 

 

 

 

You have a tectonic plate, one of the parts of earth's outer shell that moves, relative to another part. One tectonic plate diving at a gentle angle under another, but the plates stuck together where the overriding plate has its leading edge. So that the overriding plate stuck gets bulged up in between times and then during the earthquake kicks the seafloor and that helps to drive a Tsunami. It warps the seafloor. 

 

 

 

When such huge waves hit beaches, they scoop up vast amounts of sand which is left behind in layers stretching far inland. 

 

 

 

The 2004 Tsunamis was generated offshore Sumatra and also the Andaman & Nicobar Islands, north of Sumatra. 

 

 

 

It was known that an earthquake this big measuring 9.2 on the Richter scale and releasing a huge amount of penned-up energy had not happened in the Indian Ocean for at least 200 years. Now, Nature publishes the work of geologists who uncovered massive tsunamis which hit the same region about 700 and 1,400 years ago. 

 

 

 

The wave hit Sumatra first along with the Andaman & Nicobar Islands. The next place that was hit was Sri Lanka, followed by the Maldives and East Africa, Kenya and even the Madagascar.

 

 

 

Brian McAdoo and his colleagues surveyed the devastated areas of Sumatra, very soon after the tsunami hit. 

 

 

 

So about two or three kilometers of beach here is still dealing with at least 90% of infrastructure destroyed by a rather solid meter high above ground wave which maybe, two or three meters above sea level, even a kilometer under sail inland.) 

 

 

 

Have you noticed the palm tree there? Looks like it’s been wiped pretty much clean till you get to the point that's about ten meters up. It's a big wave that came through here again to trip to southwest. 

 

I saw the first wave coming with the tsunami, up to around two meters you look at from here. And it just started to destroy this place. And you can run away, because when the first wave was coming, the people shouted, "Run, run, run, run away, run away!" Something like that. 

 

Imagine a wall of water, coming edge is about ten meters high, turns out it’s about ten meters per second as the wave comes in. Hussein Bolt just won the 100 meter dash in the Olympics in just over nine seconds. If you were Hussein Bolt, you could maybe outrun this wave, but then imagine a wave comes in for one kilometer.

 

Brian Atwater and Maria Martin joined the geological team in Thailand, a country also badly hit in 2004. What they’ve found there makes them particularly concerned for the safety of people in their own very vulnerable parts of the Pacific, northwest of America. 

 

Today, a company by David Holly from the Ireland County Department of Emergency Management, they demonstrated for Nature just how tsunami geologists work. They hoped to confirm work already done by scientists from Texas and British Columbia. 

 

According to the work that was done here by Harry Williams and Ian Hutchison, throughout this area and down the road a bit, they mapped a pair of sand layers. 

 

The first place they dug quickly revealed the proof.

 

That feels sandy, huh? Okay, the best guess is this from the year AD 400 and this is close to the year AD 700.

 

Not as spectacular as the Thai layers, but it's still something real, huh?