The tsunami that struck in December of 2004 was so deadly partly because it caught so many people by surprise. But geologists believed there must be a precedent and the evidence would be buried in the soil. This geologist says it's not a matter of digging deep enough, but in the right spot. He says the right spot was in Thailand, a murky area which was inundated by the tsunami. He says the water flowed an estimated 30 feet deep and it deposited a lot of sand. The geologists reasoned if there had been a prior large tsunami, there would be a second layer of sand buried deeper. They found the layer four to five inches thick, and then did radio carbon dating on that sand, and it was dated from the 14th century. In other words, this tsunami in 2004 was the largest in 600 years. Ever since the 2004 disaster, the countries in the region have been preparing for the next giant wave. They're installing warning systems, toughening building standards, and teaching residents how to respond. But how much time and money should be spent on this if large tsunamis are so rare? The expense does seem worthwhile to those who live and work in the area. Most of the smaller tsunamis don't show up in the geological surveys, and even the larger tsunamis may be becoming more regular, as evidence suggests.