SAPPORO – Mount Usu will continue to experience small-scale phreatic explosions for the time being, but the danger of a more serious eruption still remains, a governmental panel of experts determined Sunday.
The Coordinating Committee for the Prediction of Volcanic Eruptions released the forecast after meeting in the afternoon to compile data and discuss the activity that the volcano in southwestern Hokkaido may exhibit in the coming weeks.
The panel noted that the activity of Mount Usu, which erupted Friday, “resembles the pattern observed in the early stage of its eruption in 1910,” when a total of 45 craters were created during a series of blasts that continued for more than three months.
Phreatic explosions are caused when volcanic gas heated by underground magma destroys the surface of the mountain, and does not normally result in the ejection of magma.
No lava flows have been confirmed since the volcano woke from its 22-year-long slumber on Friday.
But Hokkaido University professor Hiromu Okada, a member of the committee, warned, “In light of the past records of the volcano’s eruptions, it is unthinkable that its activity will end in small-scale eruptions as currently observed.”
The committee said eruptions and underground activity since Friday have only been detected on the northwestern slope of the volcano, repeating the pattern of the 1910 eruptions.
Although no new eruptions were reported Sunday afternoon, gray clouds of rock and steam continued to billow out intermittently from several cracks in the side of the 732-meter volcano that were created by explosions over the previous two days.
A column of grayish white smoke emanating from a crack near a Lake Toya hot spring resort nestled at the foot of the volcano reached as high as 2,700 meters at around 5:40 a.m.
A team of volcano experts led by professor Okada, who flew over the mountain to monitor the volcano, said Sunday’s blasts occurred from the same cracks as the previous eruptions and that he could see no signs that the east side of the volcano would become active.
This assessment prompted the city of Date, situated southeast of the volcano, to partially suspend its evacuation orders and allow some 2,200 residents in its Nagawa district to return home.
The town of Sobetsu, northeast of the mountain, also allowed some residents to go home.
Meanwhile, officials of Abuta, west of the volcano, ordered about 1,570 residents who had taken shelter in schools in the town of Toyoura, to move on to relief centers in the neighboring village of Toya and the town of Oshamambe so that the Toyoura schools could be used to hold classes. Another 700 Abuta residents were also moved from schools in Toyoura to other facilities within the town.
Many of the evacuees complained about being forced from one place to another since last Wednesday. Some said it was the fourth time they had been told to move.
With car traffic regulated since the eruption, the town of Sobetsu started operating chartered buses for residents to go to hospitals and stores.
The Hokkaido Board of Education decided to postpone ceremonies marking the opening of the school year for five prefectural high schools as no transportation is available for commuters due to the eruption.
The frequency of seismic tremors in the area has been decreasing significantly, a Muroran Meteorological Observatory spokesman said, adding that very few of them can be be felt by humans.
Experts noted, however, that decline in the frequency of such tremors could make it difficult for them to predict the development of the volcano’s activity.
They are also calling for continued vigilance against mudslides as a thick layer of snow, hidden by volcanic ash, still covers the mountainside. At least two people were killed by mudslides when the volcano erupted in 1977-78.