Death and Birth of An Island

The 1883 eruption of Krakatoa was just one phase in a continuing cycle of destruction and rebirth in the Sunda Strait. More than 1 million years ago, the volcano built up a cone-shaped mountain composed of alternating layers of volcanic rock, cinders and ash. The total height of this mountain was about 7000 ft (2100 m), some 1000 ft (300 m) of which was below sea level. Further activity (in AD 416, according to the Javanese Book of Kings) destroyed the top of the mountain, forming a caldera, or bowl-shaped depression. Portions of the caldera projected above sea level as the islands of Rakata, Rakata-kecil and Sertung. 

Over the years, three new cones were thrust into the air, these eventually merged into the single island that erupted in 1883. At the end of 1927, there was renewed activity on the seafloor on the line of the old cone which by January 1928 had created the small island of Anak Krakatau below sea level. Since then continued upheavals have pushed the island above sea level.