An active lava dome is growing inside the crater of Semeru volcano and there are 3 - 4 eruptions per day. It seems that the size and frequency is increasing in the past days according to VolcanoDiscovery research group that just got back from East Java.
Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. Semeru, a favorite mountain trekking destination, has been in almost continuous eruption since 1967. It is known for its regular ash explosions that typically occur at intervals of 10-30 minutes.
The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises abruptly to 3676 m above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE.
Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.