Typhoon Haiyan makes landfall
The destruction in Tacloban City on the Philippines' east coast has been described in terms that are reminiscent of recent great tsunamis - of buildings and people being swept away by a huge wall of water.
The cause is very different, of course. For tsunamis, the wall arises from an earthquake's displacement of the sea floor. In the "storm surge" that Tacloban and surrounding towns experienced, it is primarily the ferocious winds that create the unstoppable mass of water.
Several factors, though, have to come together to make the kind of phenomenon witnessed in the Philippines.
One is an extreme zone of low air-pressure, which allows the ocean to rise up.
For Typhoon Haiyan, the meteorologists were talking of 895 millibars - 100 millibars or so below what one would normally expect.
But this in itself would probably have raised the water by no more than a metre.
The winds, on the other hand, had a huge impact. They were estimated to have reached an average of 310km/h (195mph) as the storm centre made landfall.
Such force would have pushed the water even higher, particularly on the northern side of the typhoon's eye where the winds move in the same direction as the storm.
And unfortunately for Tacloban and nearby settlements, the storm followed a track that put the area full-square in the firing line.
The local geography and the shape of the sea floor would also have exacerbated the effect.
As the surge neared, it was funnelled into the bay between the islands of Leyte and Samar. The water rose so high as it came across the coastline that even those who took refuge on the first floors of buildings were swept away.
The estimates are uncertain, but the storm surge that hit Tacloban was at least two metres high and there are reports of waters reaching in excess of five metres (16ft) in places.
The forecasts were pretty good in the run up to Typhoon