Myrdalsjökull
This picture shows — obviously — a glacier. What's not so obvious is, that this glacier, like so many in Iceland, has an active volcano underneath it. This leads to accumulation of large amounts of meltwater under the glacier, which spills over and floods a large area of the southern coast every couple of years in a Jökulhlaup. The Lonely Planet guide to Iceland says that it was a couple of million cubic litres (sic!) in 1996… Wow… a couple of million m9 of water! That's a lot!
Coincidentially, what exactly I was suffering from when I drove past there and thought to myself “Who had the stupid idea of putting the glacier on top of a volcano anyway?”, I don't recall. I hadn't even had Hákarl that day…