v In 1783 an Icelandic eruption threw up enough dust to temporarily block out the sun over Europe.
v About 20 to 30 volcanoes erupt each year, mostly under the sea.
v A huge underground river runs underneath the Nile, with six times more water than the river above.
v Lake Bosumtwi in Ghana formed in a hollow made by a meteorite.
v Beaver Lake, in Yellowstone Park, USA, was artificially created by beaver damming.
