This is the sixth report on the progress of the project Volcano Monitoring and Research in Indonesia, covering the first quarter of 1987. Background information on the project and the organizational status of the Volcanological Survey of Indonesia (VSI) and the U.S. Geological Survey (USGS) were reported in an earlier report (Casadevall, 1985).
Since the end of the 1982 - 1983 eruption of Galunggung volcano, west Java, a large and growing lake has formed within the 1982 - 1983 crater. The volume of this lake in July 1986 is approximately 6.1 million cubic meters of water. This water is accumulating at a rate of approximately 2.6 million cubic meters per year.
The purpose of this report is to indicate the exixtence of a phreato-magnetic volcanic center in the densely populated area south of Cirebon city. On July 6 and July 29, 1988, I examined the geology of the area near the reservoir (waduk) Setu Patok , located 8 km south of Cirebon city (Figure 1) [108 degrees, 47', 10" S; topographic map, 1966 series, sheet 4722 IV, Tjirebon].