To add to the complexity, and thus the fascination, of the Krakataus case study, in 1930 a second order event occured. In the center of the three-island archipelago, from the waters covering Krakatau,s submarine caldera, a fourth island, Anak Krakatau (Krakatau’s child), was born after a gestation period of almost 50 years. This emergent, virgin island, of which Surtsey is the cold temperature counterpart, has grown by periodic eruption and is now 2 km (1.25 miles) in diameter, and some 270 m (over 900 ft) high. In this turn, it has also received plant and animal colonists, largely from its older companion islands, and has developed its own embryonic biological community. The changes in this community as species are added year by year and as one temporary phase of the succession gives way to the next can be followed within an ecologist’s lifetime. Anak Krakatau’s emergence has provided a second opportunity for studying one of the central questions of ecology, the way comminities of living things are assembled. So Krakataus have given us not merely a single natural experiment, but a nested pair of them.
The early work by Dutch investigators has been augmented by succeeding generations of biologists and we now have data for a period of more than a century. Since the Krakatau biota, particularly that of Anak Krakatau, is a simplified one, many general ecological questions can be examined there more conveniently and profitably than in the more complex ecosystem of mainland areas. More importantly, perhaps, the Krakataus have become a classic case study of several aspects of ecological change. These include recovery of a tropical forest ecosystem from extreme disturbance, community assembly and succession in the humid tropics, and the colonization of islands.
ADutch topographical engineer, Captain HJG Ferzenaar, was sent to reconnoiter the Krakatau group in the early August. Trees grew on the peak of Rakata but in devastated areas there were tree stumps, again without sign of branches or leaves. Volcanic effluvia prevented Ferzenaar from mapping the western, downwind half of the island, but his topographical map identifies three active craters, one on Perbuatan andnow two more on Danan, from which vapor columns rose, with many fumaroles (vents issuing gas and steam). The northernmost part of the main Danan crater appeared to have fragmented or collapsed recently. The eztent of volcanic activity convinced the wise captain that ‘Measuring s=there is still too dangerous, at least I would not like to accept the responsibility of sending surveyor…I consider a survey on the island itself inadvisable’ (Verbeek 1885). He was the last person set foot on the Island of Krakatau.
As the Dutch man-of-war Prins Hendrik passed close to Krakatau’s north coast on August 12, H McLeod (who was to be the first to set foot on the archipelago after the eruption) observed a 30-m-wide crater from which a column of ash and steam reached a height of 3400m (over 2 miles), as measured later from a suitable distance. Further ash eruptions were witnessed by ships during the next ten days. ON August 22 the Sunda, after passing the erupting volcano, sailed into a layer of pumice in Semangka Bay that was so thick that a bucket lowered overboard was filled with pumice rather than water. Activity was again intensifying. Explosions were heard in the afternoon of the twenty-fifth on the Prises Wilhelmina, near Jakarta, and in the evening ash was falling at Teluk Betung 80 km (50 miles) away in Sumatra and 300 km (190 miles ) away, south of Java’s First Point.