Various discussions have been made by many authors as respects the eruption mechanism of Krakatau caldera (e.g. Williams, 1941; Yokoyama, 1981; Self and Rampino, 1982; Yokoyama, 1982). Accumulation of geophysical data may provide important information to clarify the problem. Yokoyama and Hadikusumo (1969) have already established the gravity stations Krakatau Islands. The low residual anomalies…
The gravity survey on Krakatau Islands was first carried out by means of a land gravimeter in 1968 ( Yokoyama and Hadikusumo, 1969) and was supplemented by the present authors in 1982. The gravity points on the islands has reached 40 in number.
This study was part of a cooperative project with the Indonesian Institute of Sciences, Bandung, Java, the Michigan Technological University group (W.I Rose, Jr., principle investigator) and the Hawaii Institute of Geophysics, University of Hawaii group (G.P.L. Walker, principle investigator).
The Toba depression in northern Sumatera is a complex structure, formed by repeated episodes of caldera subsidence and resurgence, strongly influenced by regional structure. The Toba depression, and the associated Toba Tuff, a widespread ignimbrite sheet which covers approximately 20.000km, are the result of three major eruptive events.