People living around Semeru Volcano, Indonesia, have been put on alert for a potential eruption. Indonesia's Centre for Volcanology and Geological Hazard Mitigation has put the volcano on level 3 (of 4) alert and said "not to conduct activity at a radius of 4 kilometres from the crater, especially around the south-east of the volcano's slopes." There have also been reports of ash clouds (or steam) being vented from the crater.
Semeru is a very active volcano in a country full of active volcanoes. It has been erupting since 1967, quite a long span for any stratovolcano to be constantly showing signs of eruption. It is likely to erupt pyroclastic material, lava flows and domes and create lahars - it is quite the textbook volcano!