Massive amounts of volcanic gas were ejected nearly two years ago from the part of Mount Usu in Hokkaido where the latest eruptions are taking place, researchers said Monday.

At Mount Usu’s northwestern foot, where eruptions have been occurring since March 31, the amount of volcanic gas measured in August 1998 was more than 10 times that from other parts of the volcano, except for craters, the researchers said.

Elevated pressure in underground volcanic gas apparently forced some of it to the surface through cracks and fragile areas of the crust, they said.

Kenji Notsu, a professor at the University of Tokyo, and Pedro Hernandez Perez, a researcher from Spain, jointly conducted the observation for two weeks in August 1998.

Observations can help predict the places in volcanoes where eruptions will take place if data on quakes and crustal movements are examined as well, Notsu said.

Notsu and Perez measured carbon dioxide, the main component of volcanic gas, at about 180 points on the surface of Mount Usu.

The largest amount was measured over an extensive area of the northwestern foot and in active and inactive craters.

They also found the density of underground carbon dioxide at those points was more than eight times that of other parts.

Observations of volcanic gas released at places other than craters have been conducted since the 1990s at more than 10 volcanoes in the world, beginning with Mount Etna in Sicily.

The 732-meter Mount Usu has been spewing ash, steam and smoke since erupting March 31 for the first time in nearly 23 years.

Residents around the volcano were evacuated when an eruption was predicted. No injuries have been reported.

Pilotless observer

DATE, Hokkaido (Kyodo) The Meteorological Agency flew a radio-controlled plane Monday to monitor Mount Usu’s volcanic activity but failed to collect data due to strong gusts, it said.

Equipped with global-positioning equipment, the aircraft measures 2.1 meters long and 2.8 meters wide. It weighs about 16 kg.

It is the first time for the agency to use such a plane for volcanic observation.

It is scheduled to fly over the west side of Mount Nishiyama and active craters of Mount Konpira where manned aircraft cannot fly for safety reasons, agency officials said. Nishiyama and Konpira are secondary peaks on Mount Usu. The aircraft is also tasked with collecting volcanic gases and photographing the craters, they said.