Semeru (or Semeroe, Smeroe, Smiru) volcano is situated in Malang dan Lumajang region, East Java. The summit of Mt. Semeru is Mahameru
(+ 3676 m asl) which is located at 08°06’30” south latitude and 112°55′ east longitude and is the highest peak in Java. In the southern part of the summit grows the young active crater which has been erupting since the nineteenth century, namely Jonggring Seloko crater. Small vulcanian explosions have occurred at intervals of between 10 minutes to one hour. These have been the characteristic of Mt. Semeru since 1967.
The flank of Semeru streching eastward, reaches the plain of Lumajang and Pasirian. Westward, the flanks spread over the plain of Malang and Turen. Northward, the flank is bounded by Jambangan complex that consists of : Ayek-ayek, Ranu Kumbolo and Mt.Kepolo. Southward, the foot of Semeru is bounded by the southern mountain (Tertiary mountain range).
The irregular shaped of its summit is caused by frequent shifting of its eruption center in northwest – southeast direction. The present activity center is at Jonggring Seloko, a crater that appears in the southeast part of Mahameru, and it is separated by a narrow saddle. Cauli flower like eruption column is always erupted through its crater.
The eruption history of Semeru was recorded since the 19th century, started in 1818. The eruption occurs frequently, at least once a year. Since the 1818 until now there have been 82 times of eruptions.
Normally the eruption column reaches a height of 300-500 m above the crater. The eruption cloud is usually blown away by the wind. Sometimes the color of eruption cloud varies from white or greyish and blackish depends on the ash content. At night, glowing clasts is often seen that the “volcano eruption type” is interupted by “strombolian eruption type”. The ash cloud may reach a height of 4000 m above the crater, and then fall back around the crater and rolled down as far as 1500 m from the crater rim.
Big eruption is often followed by eruption generated pyroclastic flows. During active period or when the activity decreases lava flows may came out of the eruption vent, and lava tongue is formed. Because of the steep flank of Semeru, part of the lava front rolls down and glowing lava avalanches occurs, which is sometimes accompanied by”lava collapse generated pyroclastic flows” (nuee ardante). The increase activity of Semeru usually takes place in a short period of time, whereas the eruption phase takes place from several days to several months. The activity period is often interupted by rest period.
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