Semeru Volcano

Semeru volcano is situated in the Bromo Tengger Semeru National Park in south-east Java. The volcano, which rises to an altitude of 3676m at the S end of a volcanic massif extending N to the Tengger caldera, has been in almost continuous eruption since 1967. The eruptions are predominantly vulcanian in nature, although periods of heightened activity involving larger explosive events, block lava flows and pyroclastic flows have occurred. During the rainy season, huge lahars have been responsible for extensive devastation. Access to the summit region is usually permitted, yet ballistics may reach the crater rim and have caused injuries or fatalities in the past. A more detailed summary of the current eruptive phase follows.

Ash cloud from Semeru. View over Tengger Caldera with Bromo crater towards bottom left of picture.	Nighttime view of summit eruption of Semeru Volcano.

Semeru had been frequently active in the 20th century. The current eruptive phase commenced at the site of the previous 1963 eruption. In 1967, activity resumed, characterized by vulcanian explosive activity, the formation of a small lava dome and slow extrusion of block lava flows of up to 2km in length. Minor pyroclastic flow activity resulting from collapses of the block flow front were observed. A first fatality was reported in 1981, when pyroclastic flows reached a length of up to 7km during a period of heightened activity.

The eruptive activity continued to deposit material on the flanks of the volcano. On 14 May 1981, over 30cm of rain in 2 hours dislodged an estimated 5 million tonnes of material from the E flank of the volcano. The resulting lahars resulted in over 300 fatalities and even swept away a dam that had been erected after a similar event in 1901.

In March 1990, it appears that the dome was destroyed. The actual event is poorly documented apart from accounts of increased ashfall nearby, yet observations in July revealed a large pit at the former site of the dome. No new dome has been emplaced in the active Jonggring Seloko crater since then. The type of activity after loss of the dome has however remained similar to that beforehand.

On February 3rd 1994, increasing activity culminated in a powerful eruption sending pyroclastic flows up to 11.5km SE of the summit down the Kembar and Kobokan rivers. 6 Fatalities were reported in Sumbersari village. This presumably raised awareness with the authorities, so when pyroclastic flows reached a length of 9.5km on 20 July 1995, a warning issued shortly beforehand prevented any casualties. Fatalities have also occurred due to impact of ballistics near the active crater. In September 1997 two german climbers were killed, then on 27 July 2000 a group of volcanologists were surprised by an unusually violent explosion and two of them unfortunately lost their lives, with several others being injured. The most recent notable activity was reported in december 2002, when pyroclastic flows travelled up to 9km from the summit.

Due to sparse population of the region surrounding the volcano, accompanied by permanent monitoring of activity, the impact of activity has fortunately, with exception of the events mentioned above, been rather limited. Eruptions continue at present (Aug.07) with a characteristic intensity.

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