The Meteorological Agency on Saturday issued an advisory regarding Mount Asama, following a rapid increase in seismic activity in the early morning. Smoke was seen billowing to a height of about 800 meters as of 6 a.m.

The active volcano straddles the border of Gunma and Nagano prefectures and is about 150 km northwest of Tokyo. The upmarket summer resort town of Karuizawa is on the mountain’s southern slope.

The advisory was issued at 9 a.m. and by around 1 a.m., the number of volcanic quakes had begun to increase.

Between midnight and 9 a.m., 233 quakes occurred, with the focus of the quakes at a shallow depth within the crater, the agency said.

The temperature at the bottom of the crater has been rising since early May. It was 180 Wednesday, the highest figure since a local observatory began to monitor the changes in 1994.

Smoke billowed as high as 1,000 meters from the volcano on June 2 and 4.

The agency said, however, that no signs of magma movement have been observed near Mount Asama. Such signs would include volcanic tremors or changes in the earth’s crust.

“Since no quakes with seismic waves observed in the time of eruption are apparent, this development is unlikely to soon lead to a large explosion,” an agency official said. “But we want to closely monitor (the volcano).”

Meanwhile, three Nagano Prefecture municipalities in which starting points for climbs are located have asked climbers to refrain from entering the area following the agency’s advisory.

The local governments have erected signboards barring climbing at the starting points in question. The Nagano Prefectural Police conducted patrols to confirm whether any climbers had remained on the volcano.

Two municipalities in Gunma Prefecture also began gathering a variety of information, with the prefectural police setting up a liaison office.

The 2,568-meter-high Mount Asama, which was the scene of a major eruption in 1783, has had relatively small eruptions over the past decades. In 1947, 11 mountaineers died after being hit by volcanic cinders from an eruption. The last eruption, in July 1990, caused almost no damage, merely littering some areas with ash.

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