Mount Asama or (浅間山 Asama-yama) is an active volcano on Japan's central Honshū Island. It is one of the largest active volcanoes in the country, standing 2,542 m (8,340 ft) high and the most active on the island. It has a circular crater 1.2 km (0.75 mi) in circumference. It is located on the border of Gunma and Nagano prefectures, near Tōkyō.
The first recorded eruption took place in 1597. A severe eruption in 1783 destroyed several villages and a primeval forest. Since then it has erupted periodically, showering the surrounding area with ash and stones. The last major eruption was between 1 September and 6 December 2004.
However, the mountain erupted again at 1.51 am on 2 February 2009, having shown signs of unrest, beginning in late January 2009. The eruption scattered rocks more than 1 km from the crater; sent a plume of smoke 1.8 km into the sky and showered Tōkyō, 144 km (90 miles) to the south-east, with ash.