About 1,400 small earthquakes have been recorded around Mount Hakone in Kanagawa Prefecture over the past month, alarming tourists and residents, who are worried about greater possible dangers to come.
Experts say the cluster of tremors, most of which were too small to feel, have so far shown little sign of reawakening the mountain, which last erupted about 3,000 years ago.
"We need caution if the tremors become bigger. But the current situation does not point to an eruption anytime soon," said Isamu Amano, assistant director at the Hot Springs Research Institute of Kanagawa Prefecture, which tracks local volcanic activity. "We'll continue to keep an eye on the activities."
Hearts pounded at 1:15 p.m. on Feb. 10 when a magnitude 2.3 earthquake hit the Owakudani Valley, a popular tourist destination with hot springs resorts in Hakone. The Hakone Ropeway, which runs between the valley and surrounding mountains, was shut down for two hours for checks, triggering massive Twitter traffic from those worried about an imminent natural disaster.
Seven quakes ranging from magnitude 1.4 to 2.3 occurred on just two days: Feb. 10 and 16. In all, 1,400 tremors shook the area between Jan. 17 and Feb. 16, according to the Hot Springs Research Institute.
However, this flurry of seismic activity is nothing new to the region, where, 3,000 years ago, Mount Hakone erupted and created the Owakudani Valley and Lake Ashinoko, said Tomoyuki Kanno, senior analyst for volcanic activities at the Meteorological Agency.
"These quakes happen every year," he said.
But, Kanno said, the recent activity, including a series of minor rock movements and displacements, the first since 2001, bears watching.
Twelve years ago, when increased pressure in groundwater pushed up the mountain, the fumes emitted included toxic gasses, he said.