Why did so many people die in Haiti's quake?

When Pete Garratt, Red Cross head of disaster relief, received an alert on 12 January indicating a large quake had hit Haiti near its capital Port-au-Prince, he instantly recognised the seriousness of the emergency.

"I knew that meant deaths and injuries," he says.

The reason he predicted the effects of the quake would be so grave, Mr Garratt explains, is that there are a number of critical factors, learned through years of experience, that contribute to the scale of devastation following such big shifts of the Earth's crust.

One is, perhaps obviously, the size of the quake , but also how near it is to the surface, the density of the population near its epicentre, as well as whether there are any heavily urbanised areas nearby. These all indicate a higher death toll - and were all features of the Haiti quake.