During 7 January through at least 19 May 2002 at Ijen, seismicity was higher than normal. Shallow volcanic and tectonic earthquakes were recorded (table 3). One small explosion earthquake was recorded during the week of 28 January-3 February. A total of three deep volcanic (A-type) earthquakes were registered during early May. Continuous tremor occurred with a maximum amplitude of 0.5-4 mm until mid-March, when it decreased to 0.5-2 mm. During 8-14 April, a white, thin, medium-pressure plume rose 50 m above the summit crater. The following week, the tremor increased to 0.5-6 mm maximum amplitude and remained at similar levels through at least 19 May. The Alert Level remained at 2 during the report period.

Table 3. Earthquakes recorded at Ijen during 7 January through 19 May 2002. Courtesy VSI.

Geological Summary. The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the rim was buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Kawah Ijen is the site of a labor-intensive mining operation in which baskets of sulfur are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor; nearby waterfalls and hot springs are tourist destinations.

Information Contacts: Dali Ahmad, Volcanological Survey of Indonesia (VSI) (URL: http://www.vsi.esdm.go.id/).