Eyewitnesses of the tsunamis that hit South Asia following Sunday's underwater earthquake said the wall of water hit without warning, but a German seismologist said that, in principle, a warning was possible.
Sunday's earthquake measured 8.9 on the Richter scale
The waves that came crashing onto Asia's southern shores were tens of meters high. They destroyed houses and hotels, flooded entire villages, and by latest accounts, swept more than 20,000 people to their deaths. Thousands more are injured, homeless, or counted as missing.
Eyewitnesses such as Deutsche Welle correspondent T.S.V. Hari in Madras, India, reported that the tsunamis came out of nowhere.
People look at a car and debris that was washed by tidal waves in Madras, in the southern Indian state of Tamil Nadu, Sunday, Dec. 26, 2004. A massive tidal wave triggered by an earthquake in Indonesia slammed into several parts of southern India Sunday killing at least 286 people, most of them in Tamil Nadu state. The U.S. Geological Survey said the 8.9-magnitude earthquake in Indonesia is the largest in the world in 40 years. (AP Photo/M.Lakshman)
"There was absolutely no warning, it all happened so suddenly," Hari said. "There was just this huge wall of water. And it was only a matter of minutes before this huge wave reached people here."
"Cars, people, cattle -- everything in its path was just swept away," he recounted.
The tsunamis were caused by an underwater earthquake close to the island of Sumatra. The quake measured 9.0 on the Richter scale -- by far, the strongest earthquake to have hit in over 40 years.
What is a tsunami?
Scientists explained that the area just off Sumatra's southwest coast is particularly dangerous, as it's where two tectonic plates meet, grinding together and sending periodic tremors throughout the region. With Sunday's violent rupture, the seafloor was shunted vertically by about 10 meters, generating a massive wave, said Rainer Kind, seismologist at the geological research center in Potsdam.
Map showing the epicenter of the devastating earthquake
"We're talking about violent shifts in the sea floor, which of course resulted in the displacement of masses of water. The wave which formed fanned out in all directions on the open sea. From ships sailing in the area, the waves are difficult to recognize. But when such a wave hits a coastal area, it can easily build up into ten-meter high waves, which have devastating consequences," Kind said.
Warning is possible
Kind acknowledged that the quake itself would have been impossible to predict, as scientists still know too little about what happens deep inside the earth's core. But, he said, an early warning about the dangerous tsunamis certainly would have been possible.
"Tsunamis are predictable, because once there's been a quake, you know that a tsunami could develop. And then you could predict that after so many hours, the waves would hit, for example, Sri Lanka or India. These countries could have had the situation better under control. But, as we've heard, the Indian Ocean doesn't have such an early warning system in place, unlike the Pacific Ocean."
A warning center such as those used around the Pacific could have saved most of the thousands of people who died in the tsunamis in Asia, said Waverly Person of the United States Geological Survey.
"Most of those people could have been saved if they had had a tsunami warning system in place or tide gauges," he said.
"I think this will be a lesson to them," Person said, referring to the governments of the devastated countries.
Once an underwater earthquake hits, there is usually time -- from 20 minutes to two hours -- to get people away from the shores as the tsunami builds in the ocean.
"People along the Japanese coasts, along the coasts of California -- people are taught to move away from the coasts. But a lot of these people in the area where this occurred -- they probably had no kind of lessons or knowledge of tsunamis because they are so rare," Person said.
More waves to come?
Kind didn't exclude the possibility of further after-shocks and more tsunamis in southern Asia.
"Since the main quake, there have already been several strong after-shocks in the region north and south of the epicentre. We can't yet predict when the quakes will be over. There could be a second strong quake at anytime, which could result in further tsunamis," Kind said.
US seismologists disagreed, saying it was unlikely the Indian Ocean region would be hit again anytime soon because it takes a very strong earthquake to trigger a tsunami.