Forty four years after the main explosion, in 1927, volcanic activity was seen in the sea covering the old caldera, between the sites of the two northernmost former volcanoes of Krakatau, where the greatest activity had occurred at the time of the cataclysm. A series of eruption 185 m below the surface of the sea resulted in the emergence of three new islands, one after the other. They were all son destroyed by surf. A fourth emerged from the sea on August 12th 1930. It remained above water, and was aptly named Anak Krakatau( child of Krakatau ). This young and active volcano has been growing around 6 feet a year and still continues doing so. It grew by the accumulation of ash, and suffered a devastating eruption in 1952, and other very destructive one in 1971. It is now 300 m high and 5 Km in diameter, and is still active spurting fire and cinder, this like moonlike landscape. It is lonely volcanic island in the middle of the sea. The northeast coast, north foreland and east foreland are now vegetated; the succession of vegetation is still at an early stage, Casuarinas equisetifolia (cemara) being the dominant tree.
Verbeek, in his report on the eruption, predicted that any new activity would manifest itself in the region which had been between Perboewatan and Danan. This prediction came true on 29 December 1927, when evidence of a submarine eruption was seen in this area (an earlier event in the same area had been reported in June 1927). A new island volcano, named Anak Krakatou or Child of Krakatoa rose above the waterline a few days later. The eruptions were initially of pumice and ash, and that island and the two islands that followed were quickly eroded away by the sea. Eventually a fourth island named Anak Krakatau broke water in August 1930 and produced lava flows faster than the waves could erode them. Of considerable interest to volcanologists, this has been the subject of extensive study.
Anak Krakatau has grown at an average rate of five inches (13 cm) per week since the 1950s. This equates to an average growth of 6.8 metres per year. The island is still active, with its most recent eruptive episode having begun in 1994. Quiet periods of a few days have alternated with almost continuous Strombolian eruptions since then, with occasional much larger explosions.
The most recent eruption began in April 2008, when hot gases, rocks, and lava were released. Scientists monitoring the volcano have warned people to stay out of a 3 km zone around the island.
On 6 May 2009 the Volcanological Survey of Indonesia raised the eruption alert status of Anak Krakatau to Level Orange.
The islands have become a major case study of island biogeography and founder populations in an ecosystem being built from the ground up in an environment virtually sterilized.
The islands had been little explored or surveyed before the 1883 catastrophe—only two pre-1883 biological collections are known: one of plant specimens and the other part of a shell collection. From descriptions and drawings made by the HMS Discovery, the flora appears to have been representative of a typical Javan tropical climax forest. The pre-1883 fauna is virtually unknown but was probably typical of the smaller islands in the area.