Areas near Mount Zao rumbled with heightened seismic activity Tuesday after warnings that a potential eruption could threaten a popular Tohoku ski resort in the area were issued the previous day.

The volcano sits on the border of Miyagi and Yamagata prefectures, where 12 volcanic earthquakes had occurred by 11 a.m. Tuesday. The Meteorological Agency issued a volcanic warning the same day for areas around the crater — its first for the Zao area.

The agency warned the public to be on the lookout for falling rocks in areas within 1.2 km of the crater. The warning follows last year's deadly eruption of Mount Ontake, on the border of Gifu and Nagano prefectures. Ontake, which erupted without warning, ejected rocks, boulders and other debris over a wide area and was the worst volcanic disaster in the postwar era.