SAPPORO – At least three fault lines have appeared near a crater on Hokkaido’s Mount Usu, where an explosive eruption occurred Friday, a group of volcano experts said Monday.
The group’s leader, Hiromu Okada, a professor at Hokkaido University, said the fault lines may be preliminary signs that a lava dome is building up beneath the volcano.
A lava dome occurs after eruptions, when lava within the crater accumulates and creates bulbous mounds.
The faults are on the northwest side of the mountain, to the south of the crater. The longest one stretches over several hundred meters and the vertical displacement of each is about 1 meter, Okada told a news conference.
The discovery prompted the Meteorological Agency to issue an advisory in the afternoon, warning residents and authorities to prepare for a possible disaster.
They said pyroclastic flows could soon come streaming down the mountain and head toward the nearby Pacific Ocean coast. The flows can be extremely dangerous as they bury and burn everything in their path. They also warned of the possibility of an explosive eruption.
Okada and his colleagues have been conducting aerial observations of the mountain.
The 732-meter mountain blew its top Friday after 23 years of inactivity.
On Monday, several craters at Mount Usu’s northwestern foot intermittently released smoke.
However, the frequency of earthquakes in the area is tapering off. On Monday morning, only one or two tremors were recorded per hour, none of them strong enough to be felt by humans, according to the Meteorological Agency’s Muroran Meteorological Observatory, located about 30 km southeast of Mount Usu.
In the days leading up to Friday’s eruption, the area had been experiencing around 50 tremors per hour. ,including some strong earthquakes.
The Coordinating Committee for the Prediction of Volcanic Eruptions on Monday maintained its warning that the current pattern of volcanic activity could continue for a while.
The committee, which is made up of volcano experts, is an advisory body to the head of the Meteorological Agency.
A thick plume of smoke climbing 1,000 meters into the sky was observed Monday, rising from a crater on the western face of Mount Kompira, which is part of Mount Usu, near a hot spring resort at Lake Toya, the observatory said. The smoke was reportedly drifting to the southeast.
Meanwhile, thousands of nearby residents remained in evacuation centers, although evacuation orders were lifted for some areas around the volcano.
In Date, a city southeast of Mount Usu, the temporary lifting of an evacuation order allowed about 2,200 residents to return to their homes Sunday. In the town of Sobetsu, northeast of the mountain, evacuees were given the option of returning home.
Nearly 5,000 residents of Date, Sobetsu and the town of Abuta spent another day at the shelters.
The three municipalities are located at points forming a triangle around the mountain.
The Hokkaido government plans to start installing computers with Internet access at shelters to provide evacuees with updates on the volcano. Six shelters in Date and Sobetsu will be the first to be afforded Internet access.
The Red Cross has been setting up counseling centers at the shelters to deal with evacuees who are suffering from stress.