Four hikers lost their lives due to volcanic gas in a summit (Numano-daira) crater on 15 September. A party of 14 enjoyed hiking near the summit in foggy and calm condition. They lost a mountain trail near the western mouth of the crater, the lowest level on crater rim. They then wandered into the crater, looking for the trail. Three people fell in the southwestern part of the crater floor, and a person who tried to help them did too. The rest of the party harriedly climbed up the higher levels. Along the trail, notice boards for volcanic gas danger zone stood for hikers.
According to Jun-ichi Hirabayashi, Kusatsu-Shirane Volcano Observatory, Tokyo Institute of Technology, fumarolic gas from the southwestern part within the crater, contained 0.5 % of SO2, 60-65 % H2S and 33-37 % CO2 as dry basis, and gas collected this July from a mud pond on the crater floor contained H2S of 41% and CO2 of 56%. He pointed out inhalation of H2S as the most possible reason of this fatality. Volcanic gas probably accumulated in the low level due to no wind condition.
JMA issued "Volcanic Observation Report on Adatara Volcano, No.1" in the afternoon, September 15, in which this volcano has raised its activity these years, such that mud was spouting from two ponds on the crater floor and fumarolic activity has heightened in the southwestern part. They gave the public warning of danger to approach the crater area. JMA observed no volcanic tremors at this volcano these months, except for 5 volcanic earthquakes in August.
View of the Numano-daira crater by T. Chiba and T. Kamoshida.
Photographs of recent activity and QT movies of the Numano-daira crater in HP's by Geological Survey of Japan, and Tatsuro Chiba.
These are in Japanese, but contain views of mud spouting in the crater floor, a cartoon showing fumarolic sites in and around the crater; photos and movies mainly taken in May 1997.
Information contacts: Jun-ichi Hirabayashi (Kusatsu-Shirane Volcano Observatory, Tokyo Institute of Technology), firstname.lastname@example.org; Noritake Nishide (Sendai District Meteorological Observatory-JMA); email@example.com; Yoshihisa Kawanabe (Geological Survey of Japan), firstname.lastname@example.org; Tatsuro Chiba (Asia Air Survey Co. Ltd.) , email@example.com; Volcano Research Center (U-Tokyo), firstname.lastname@example.org.
(September 19, 1996; modified on October 2)
HEARING SURVEY by Tatsuro Chiba, Asia Air survey Co. Ltd., indicates that mud effusion on the Numanotaira crater floor had occurred in July and August this year. The scenery showing bobbling in mud pond within one of crater-pits, was taken as a movie by the Asahi TV company in the mid-August. According to T. Chiba, two of three crater-pits had been formed already before September 1st. The third pit of mud effusion may have appeared on September 1st. No report showing the increase in activity had come since the last one.
Old documents and reports on THE 1900 ERUPTION at Adatara Volcano, which were summarized by Keiichi Sakaguchi, Geological Survey of Japan, showed that the July-1900 eruption, which was preceded by small-scale phreatic eruptions (mud and sulfurous mud effusion with small ash eruption) in the previous year, issued dark-colored eruption columns with rumbling, successively three times from the central crater, which was open to the west. Soon after the eruption, the mixture of gas, ash and blocks rushed down to the west, along a valley. Sulfur refinery was situated around the crater. Unfortunately the refinery workers were accustomed to rumbling of small eruptions at this Volcano, which frequently occurred in the previous year. Only one person could have a narrow escape from there. The next day, many burnt bodies of the workers without their cloths were found on a road from the refinery; probably they took off cloths during running as they could not stand high temperature. All trees died off, losing their leaves. Houses in a village about 2.5 km away from the crater, were broken partially by the blast. It is likely that pyroclastic surges attacked the refinery and a village, killing and injuring about 80 people.
(September 14, 1996)
SEPT. 1ST ERUPTION
A very small-scale phreatic eruption (?) occurred on September 1st, 1996. Mud sprayed about 100 m from small pits was recognized by a survey team of the Japan Meteorological Agency at the summit area, Numanotaira, in September 4. Strong sulfurous gas was also felt by them. According to hearing survey done by JMA, it became clear that the eruption probably took place on September 1st; some mountaineers witnessed it and some of them took its pictures; three small pits were left behind by the mud eruption. No evident seismic activity had been recorded just before or during eruption, although the Tohoku University and JMA keep monitoring this volcano seismologically. Volcanic tremors were observed three times in April and once in June in the JMA net. No evident phenomena implying the increase of the activity had been detected after the eruption. Such the phenomena is the first time since 1965 when monitoring started at this volcano.
BACKGROUND OF ADATARA
Adatara Volcano, situated about 15 km southeast of Fukushima city, lies on the volcanic front of NE Japan. It is composed of three cones (Maegatake, Osoyozan and Adatara) of basaltic to andesitic in composition, occupying an area of 9 km EW by 14 km NS. The summit (Adatara, 1,709 m high) is a lava dome. Historically evident eruptions are limited within the Numanotaira Crater (1.2 km across and 350 m deep) at the summit, which was surrounded by fumarolic and hot spring areas.
1) The number of fumarolic pits and amount of steam had increased since the end-1898. Flare of fire was observed, being associated with large sounds in August, 1899. Ash and sulfur-rich mud were erupted, and the rim of the crater was destroyed the next day. Cinders with black smokes were erupted again three months after this event.
2) In July 1900, Hot ash and cinder were erupted; as a result the crater enlarged as large as 300 long and 150 m wide. The volume of erupted materials was estimated as 1.1 million c.m.; seventy-two people dead and ten injured probably by pyroclastic surge (?).
3) The eruption column reached at 50 m in February 1950.
Information contact: JMA, link to Chiba 's photo page