They just raised the Hakone volcano alert level from 1 to 2. Mt. Hakone is just 40 miles from Tokyo.
An earlier article from the Japan Times:
The number of volcanic earthquakes recorded in Hakone, Kanagawa Prefecture, surged Tuesday, with 98 recorded before 3 p.m. compared with 34 for all of Monday, the Meteorological Agency said.
The agency said it still believes the possibility that the Hakone volcano will erupt is low, and it is maintaining the alert level at 1 on the scale of 5. Level 1 means “normal.”
However, hot steam could suddenly be expelled from the ground in or near the popular Owakudani Valley, the agency warned, urging people not to enter areas designated as off-limits.
“Shallow hot-water activity in parts of the Owakudani Valley has become unstable,” the agency said in an advisory.
“There is a possibility that a minor ejection (of hot steam) may suddenly occur,” it said. “Please do not enter danger zones.”
The warning, which comes in the middle of the Golden Week spring holidays, is expected to affect tourism there as some 20 million people, including many foreign tourists, visit the scenic area on an annual basis. It is one of the country’s most famous hot-spring resorts.
Of the quakes Tuesday, two that shook the area between 6 a.m. and 7 a.m. were strong enough to be felt. They registered level 1, or the lowest, on the Japanese intensity scale of 7, the agency said. The focus of both was about 10 km underground.
Local officials have barred visitors from entering recreational trails and hiking courses in the valley.
The number of volcanic quakes began to surge April 26, though only two were recorded last Friday.
However, 37 earthquakes were recorded Saturday, followed by 36 on Sunday and 34 on Monday.