The Volcano Today: Will It Blow Again?

By the mid-1990s the island had overtopped both Panjang and Sertung islands, reaching a height of about 300 meters, with a diameter varying between 3 and 4 kilometers. It has some way to go before it reaches the height of the last fragment of the 1883 volcano Rakata, at some 780 meters. What are the chances of the cycle of growth and violent destruction repeating itself? Volcanologists have a number of means of assessing the likelihood of catastrophic eruptive activity. One important measure is the silica content of the ejecta. As the magma increases in silica content its viscosity increases, making it more difficult for contained gases to escape. When they do, there is a cataclysmic eruption, and silica content then falls to begin the cycle again. The Krakatau data broadly fit this model, and do not suggest that another caldera collapse event is imminent. But you can never be certain with volcanoes. In any event, it is not a volcano to take lightly. Over the last 70 years, it has deposited something like a meter of volcanic ashes on Panjang and Sertung islands, and has repeatedly cut-back the development of its own ecosystems. When in full eruption, it is an awesome sight, with huge volcanic bombs thrown hundreds of meters from the eruption center, and great plumes of ash ascending many hundreds and sometimes thousands of metres. Recent outpourings of lava have also been spectacular, for instance, in November 1992, a four day period of activity saw 35,650 square meters covered by lava of about 5 meters in thickness -- an estimated volume of over 2 million cubic meters.