Waves, of course, have two parts: the peak and the trough.
With a tsunami, the trough (the low point of a wave) is the first part to arrive, causing the sea to recede far from the shore — a telltale sign of an impending tsunami.
Tsunamis at sea and shore Tsunamis at sea are not the monster waves that might be imagined — they are at most a few meters high and are spread over tens to hundreds of kilometers.
[Album: Monster Waves]As the tsunami approaches a shoreline, where the rise of the continental slope means water levels are shallower, the wave begins to narrow and become higher.
This story might not have captured my attention if it hadn’t been for a fortuitous coincidence.
The day before, an engineering colleague, Eiichi Taniguchi, had told me that researchers at Tohoku University in Sendai, Japan, had found sediments indicating that a huge tsunami had hit Miyatojima about 1,000 years ago.
Tragically, not everyone made the right choice; I was told of at least one person who died.
Later, I saw the shrine — a simple clearing by the side of a hillside road, with stone tablets and roughly made figures — and I heard the old story and the new one again: A community remembered what it had been told and did the right thing. A message sent into the future 1,000 years ago did.
Village elders had reviewed the local temple’s records and found reports pinpointing a large tsunami 1,142 years ago.
It was most likely the result of the massive Jogan Jishin earthquake of 869, which devastated the Sanriku coast.