The ground level in the Owakudani hot-spring area of Mount Hakone has risen by up to 12 cm since mid-April, days before volcanic activity intensified in the popular tourist spot, according to a geographical survey institute.

The alert level for Mount Hakone, some 80 km southwest of Tokyo, has been raised to 2, which advises against entry to areas around the volcanic vent. Alert level 1 means the situation is “normal.”

An analysis of satellite data found that the ground level rose by up to 12 cm between April 17 and May 15, the Geospatial Information Authority of Japan said Saturday on its website.

So far, the agency has observed the ground raised by crustal deformation in an area around 200 meters in diameter in the volcano’s Owakudani district, but it said the scope of such activity has not changed drastically.

The number of volcanic earthquakes at Mount Hakone has spiked since April 26, leading the Meteorological Agency to advise local residents and tourists to stay on alert against a possible steam eruption.