From the UK Guardian:
Mount Asama, one of Japan's most active volcanos, spewed ash and smoke up to 2,000 metres into the air in an eruption early today.
2,568-metre volcano sent chunks of rock hurtling as far as 1km away,
Japan's meteorological agency said. No damage or injuries were reported.
The town of Karuizawa was blanketed in a fine layer of powder, while light clouds of ash reached Tokyo, 90 miles away
Video of the steam-spewing volcano:
Japan is a pretty dangerous place, geologically. They've got a ton of active volcanoes, and I feel earthquakes around once a week. No volcanoes too close to Tokyo, though (so far as I know), so I'm not that worried.