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November 25, 1994

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Eruption of Gunong Merapi, Indonesia

Mount Merapi, a 2,911-meter-tall volcano on the island of Java in Indonesia, erupted on November 22 at about 10:15 a.m. local time. Inconsistent news reports on the number of casualties suggest that at least 34 people were killed, several hundred were injured, and hundreds of homes were destroyed. The eruption began with steam explosions and ejection of rocks and gravel over the surface of the cone. The steam plume reached about 800 meters high. After 25 minutes of such activity, the main eruption began and sent an ash column roughly 10 kilometers high. An advisory was issued to warn aircraft from entering the ash plume and being subject to engine damage and endangering the lives of those onboard. Ash fallout was heavy as far as 45 kilometers to the northwest of Mount Merapi. On the ground, a pyroclastic flow of hot ash, gas, and other suspended particles swept 6 kilometers to the southwest down the Boyong River drainage and through Turgo Village in the Yogyakarta District. Many of the injured suffered severe burns from the hot gases. Most of the casualties appear to be in two small villages. More than 6,000 people have been evacuated from the area.

Mount Merapi has a history of violent eruptions that led to its designation as one of the "Decade Volcanoes." These volcanoes have been identified by the International Association of Volcanology and Chemistry of the Earth's Interior as requiring special study because of the danger they pose to populated regions. Mount Merapi's last large ash eruption occurred in 1984. A particularly devastating eruption took place in 1930, when 1,300 were killed by an eruption here. Another eruption, in 1976, killed 28 people and destroyed homes of 1,176 people. Today, 50,000 people live on the southwest flank of the volcano, and the city of Yogyakarta is only 35 kilometers away. Since 1984, Mount Merapi had erupted repeatedly as glowing avalanches flowed from a growing lava dome, much like the dome inside Mount St. Helens in Washington State. These glowing avalanches, or nuee ardentes, moved down a different river drainage towards the west.

Mount Merapi is monitored by the Volcanological Survey of Indonesia, which mans seven volcano observatory stations on the mountain. One of these stations had to be abandoned because of the eruption. Starting in 1981, scientists from the Branch of Volcanic and Geothermal Processes of the United States Geological Survey helped train scientists and technicians of the Volcanological Survey of Indonesia. A succession of USGS staff spent several years in Indonesia assisting with equipment installation and training. In more recent times, several members of the current staff of the Volcanological Survey of Indonesia have been trained during the summer program at the Center for the Study of Active Volcanoes (CSAV) at the University of Hawaii at Hilo. This summer program is specifically aimed at training scientists from less-developed nations in the techniques employed to monitor active volcanoes.

Each eruption teaches us more about how to identify eruptions before they occur so that people can be evacuated to safe ground. In the case of Merapi, we have learned that a volcano that has been active in one area does not always continue to erupt in the same area. The dome on the west flank of Merapi has erupted episodically since 1984, but it was not the location of the current eruption. This lesson can be translated closer to home with the ongoing eruption of Kilauea. Kilauea's eruption has been located within a confined area along the east rift zone near Pu'u 'O'o for nearly 12 years. When changes occur, such as a pause in activity, we expect the activity to return to the same area. However, for the eruption near Pu'u 'O'o to end, it is likely that a different eruption will occur along the southwest rift or at lower elevation along the east rift zone. Like the change in activity at Merapi, such a shift in the location of the eruption here will be difficult to forecast because of the ongoing activity. However, indications of such a change should be seen within the few hours preceding the outbreak of a new eruption.


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Updated: 26 March 1998