The magnificent eruption of Krakatoa was a small island that turned into a volcano and its explosive eruption in 1883 was one of the most catastrophic in history.
After the explosion, only a small islet remained in a basin covered by 900 feet of ocean water; its highest point reached about 2,560 feet above the surface.
As much as 200 feet of ash and pumice fragments had accumulated on Verlaten and Lang islands and the remaining southern part of Rakata. Analysis of this material revealed that little of it consisted of debris from the former central cones: the fragments of old rock in it represented less than 10 percent of the volume of the missing part of the island.
Most of the material was new magma brought up from the depths of the Earth, most of it distended into pumice or completely blown apart to form ash as the gas it contained expanded. Thus, the former volcanic cones were not blown into the air, as was first believed, but sank out of sight, the top of the volcano collapsing as a large volume of magma was removed from the underlying reservoir.
Enough spoiling, come watch the full video of Krakatoa below: