The activities and magmatic cycles of the Krakatau Volcanic Complex are closely related to the goology and tectonic position of Strait Sunda, which are more related to Sumatra than to Java. The basoment of Strait Sunda consists of ignimbrites and acid tuffs of 0.1 million year old, and the thormal gradient in and around Sunda Strait is about 6.7°C por 100 meter. Tectonically, strait Sundo is a…