Volcanic activity continued through January-March 1995, sending grayish white plumes 150-500 m above the summit. Sounds like thunder were sometimes heard at the VSI observatory . . . and glow was visible at night as high as 50 m above the summit. The daily number of explosions in January and early February fluctuated between 50 and 150 events. From mid-February to mid-March the average number of explosions increased to 150-200 events/day (figure 10).

Figure 10. Daily number of explosion earthquakes (bars) and height of the ash plume (line) at Krakatau, January-March 1995. Courtesy of VSI.

Geological Summary. The renowned Krakatau (frequently mis-named as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption caused more than 36,000 fatalities, most as a result of tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: W. Tjetjep, VSI.