Semeru also Mount Semeru or Gunung Semeru - located in East Java is the highest mountain on the island of Java, Indonesia and one of its most active volcanoes.
Known also as Mahameru the (Great Mountain), it is very steep rising abruptly above the coastal plains of eastern Java. Maars containing crater lakes have formed along a line through the summit of the volcano. Semeru lies at the south end of the Tengger 

        Typically eruptions occur every 20-30 minutes, with ash emissions to 100-400 m above the crater, and projectiles ejected onto the crater rim. 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.

          The eruption cloud is usually blown away by the wind. Large eruptions are often followed by generation of pyroclastic flows. Semeru volcano is the highest in Java and one of the most active volcanoes in the world. Semeru volcano has been the site of numerous deaths, the most recent being in August 2000.

            Increased activity has been reported at Semeru volcano in Indonesia. Between 6th February and 4th March 2009 there were 873 explosion earthquakes registered, with an average of 34 events per day. On 5th March there was one period of tremor recorded. On 6th March one episode of tremor was recorded accompanied by booming sounds which were heard at Semeru observatory. On 6th March at 10:28 hr a booming noise was heard while the summit was covered in cloud. Semeru is at level 2 alert (Waspada) out of a maximum of 4. Explosions occur at an interval of 20-30 minutes, with ash emissions 100-400 m above Jonggring Seloko crater. So far the current eruptions have not been accompanied by pyroclastic flows, but this remains a danger. Areas which may be affected by pyroclastic flows include inhabited areas of Rowo Baung, Supit, Pronojiwo, Urip, and Umbulandi Urang Supit. Rowo Baung and Supit are the nearest villages to the eruptive centre, 9 km from the peak of Gunung Semeru. There is a potential threat to sand mining activities at Supit and Rowo Baung. Recommendations from the Indonesian Centre of Volcanology and Geology are that people avoid the area 4 km SE of the active crater at Semeru due to the threat of pyroclastic flows. People are advised not to climb to the summit peak (Mahameru). Residents should prepare for possible ashfall. Aircraft should beware of explosion hazards, and ash emissions from Semeru.