ME-AKAN (MEAKANDAKE), Hokkaido
Researchers of Hokkaido University, Geological Survey of Japan (Hokkaido Branch), Geological Survey of Hokkaido, and JMA (Sapporo and Kushiro) surveyed ash deposits of the 9 November eruption, and examined ash under the petrological microscope. They estimated mass of the deposits as small as about 1,000 ton, smaller than that of the 1996 eruption (roughly 2,000 ton; see below). The ash consisted of older (altered) rock-fragments (andesite), minerals and clay. They found trace amounts of angular, fresh basalt fragments containing gray glass. They presented a possiblity that new magma reacted to water in a hydrothermal system, resulting in phreatomagmatic eruption in which chips of solidified new magma were issued together with larger amounts of fragments of older rocks altered hydrothermally beneath the crater.
Information contact: Mitsuhiro Nakagawa, Graduate School of Science, Hokkaido University, e-mail: email@example.com
According to "Volcanic Advisories" # 1 and 2, and "Volcano Observation Reports" on Meakandake Volcano, issued from JMA on the 9 November evening, a small-scale eruption occurred in the afternoon of this day; new ash deposits were found near the Lake Akan. Trace amounts of ash deposits were distributed up to about 10 km east from the summit crater. Seismometers of the JMA and the Hokkaido University detected a tremor event for about 4 minutes since 14:41, though no more volcanic earthquake and tremor events after it.
According to Asahi Shinbun (newpaper), an aircraft of the company flew about the summit area of the Meakandake Volcano, covered slightly with snow, around 9 a.m., 10 November. White-colored smoke was issued up to 700 m above the Ponmachineshiri crater. From the aircraft, it was observed that snow fields south and east of the crater, up to 1 km, become gray in color.
Information contact: J. Miyamura, Sapporo District, Japan Meteorological Agency, e-mail; firstname.lastname@example.org, Asahi Shinbun, http://www.asahi.com/
Summit view of Ponmachineshiri, Me-Akan Volcano before eruption. Aonuma crater with water in front, 1-st crater in center, and 4-th crater with smoke in right. Courtsey of Dr. Keiji Wada, Hokkaido Univ. of Educ. Asahikawa
Helicopter shots by Prof. Yoshio Katsui on 22 November 1996 (after eruption) and nice air-photos of craters taken by Kokusai Kogyo Co. Ltd. on 24 November in Keiji Wada's Me-Akan page (all in Japanese)
Information contact: Keiji Wada, Hokkaido University of Education at Asahikawa. fax +81-166-52-2108, e-mail email@example.com, and Volcano Research Center, ERI, U-tokyo.
Total amount of tephra erupted in 21 November was reported as ca. 25,000 t based on the field survey by a group of geologists (leader: Prof. Tad Ui) in the early-December. This amount is about 1/10 of the tephra (ca. 300,000 t) erupted at Hokkaido-Komagatake Volcano on 5 March 1996. They concluded that the 21-November eruption was very small in scale. The distribution maps of the tephra are shown at the site of petrological and volcanological group of Hokkaido Univ. (in Japanese).
Ash issued in the November 21 eruption and collected by the Tsubetsu Town, was analysed petrographically by Prof. Tadahide Ui and his colleagues of Faculty of Science, Hokkaido University. In the November 24-afternoon, Tad Ui reported no finiding of juvenile materials, such as vesiculated fresh glass particles, in it, and continued that their petrographical analysis supported the conclusion gotten by the Disaster Prevention Committee (DPC), Hokkaido Prefecture, based on helicopter inspection on November 22; that is, the November 21 eruption was phreatic without any indication of magma ascent. Tad Ui is one of the DPC members and did the air inspection on November 22.
Information contact: Tadahide Ui, Graduate School of Science, Hokkaido University. fax +81-11-736-2073, e-mail: firstname.lastname@example.org,, and Volcano Research Center, ERI, U-tokyo.
(11/22/96 part 2)
In the afternoon of November 22, volcanologists belonging to the Disaster Prevention Committee, Hokkaido Prefecture, reported after helicopter inspection that eruption occurred at the 4-th crater of Ponmachineshiri, which appeared with other three craters in the 1955 eruption. Vertically rising eruption clouds were observed from the significantly widened 4-th crater; before eruption they were growing laterally from the crater bottom. The ash-covered area extended to the NW to N areas of the crater, and new cinders were observed within the area 250-300 m south of the crater. They concluded that the eruption of the previous day was phreatic as small as one from the 1-st crater which occurred in 1988. According to JMA, the total numbers of volcanic earthquakes are 226 in November 21, 163 in the November 22-morning, 5 during the first three hours in the afternoon, and zero during the second three hours. No volcanic tremors had occurred after the 17:55 event of the previous day. The eruption cloud which could be observed in the afternoon of November 22 was white in color and 200 m high, as low as before eruption in the previous day.
(11/22/96 part 1)
In the evening of 21 November, Dr. Yuichi Nishimura of UVO (Usu Volcano Observatory, Hokkaido University) dropped a mail into the "funka"-net (volcanic eruption mailing-list for Japanese volcanologists), reporting the eruption at Me-Akan Volcano; a relatively large volcanic earthquake occurred at 17:55 JST of the day, followed by continuous volcanic tremors which decreased the amplitude with time. No air wave (shock type) was observed, being associatted with the first earthquake. Small earthquakes had intermittently taken place by at least the time when he reported. Several news on ash falling came, one of them from the Tsubetsu Town, 30 km north of the volcano. Before and after the eruption tiltmeters did not show any detectable change. He was reporting that, although the earthquake activity had been in a high level since August of this year, there had been no abrupt increase of number of earthquakes before the eruption.
JMA (Japan Meteorological Agency) issued officially the information on the Me-Akan eruption in the November 21-evening. It was reporting that the number of volcanic earthquakes after the relatively large earthquake with the seismometer saturation around 17:55 reached 158 (during about 3 hours), while that during 23 hours of this day is 185. No volcanic tremors had occurred after the 17:55 event. Stuffs of a fire station in the Tsubetsu Town and of the JMA-Abashiri branch recognized ash-falling. This is the first eruption since February 18, 1988. Helicopter inspection of the eruption was scheduled by JMA on November 22.
Information contact: Yuichi Nishimura, Usu Volcano Observatory (UVO), Hokkaido University (email@example.com), and Volcano Research Center, ERI, U-tokyo and Japan Meteorological Agency (JMA).
Me-Akan Volcano is a group of andesite cones, standing on the southwestern rim of the Akan Caldera of 24 km long (NE-SW) and 13 km wide. The highest summit, Ponmachineshiri, is 1,499 m above sea level. Me-Akan is thought to have started its growth at least 20 ka. The Nakamachineshiri crater in the center of the volcano and the Ponmachineshiri crater have active fumaroles; the latter and hot spars are distributed on the flank and slopes. Historic eruptions are phreatic one; at least, 17 eruption events in 1900's. They concentrate at both the Nakamachinedshiri and Ponmachineshiri craters. The largest volume of eruption products (tephra) was around 70,000 m^3 in the 1956 event. The latest eruptions before this time occurred in January and February 1988; ash emitted from the Ponmachineshiri crater. Volcanic activity of this volcano has been monitored by both JMA and UVO (Usu Volcano Observatory, Hokkaido University).
Information contact: Volcano Research Center, ERI, U-tokyo.
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