2018 eruption of Kusatsushirane (Motoshirane) volcano

29th January, 2018

Reexamination of volcanic vent distribution from the eruption on 23rd January, 2018 at Kusatsushirane volcano.

Overview: After the eruption of Kusatsushirane volcano on 23rd January 2018, observation from a helicopter (air craft operated by Yomiuri Shimbun) was carried out in the afternoon of 28th January. By reviewing the taken pictures, another chain of eruptive vents was found mid-wet on the Kagamiike crater-floor (approx.100m in length), in addition to the chain of volcanic vents at Kagami-ike northern crater and a small vent at the western side.

  • Many impact craters are found on the Kagamiike crater-floor, which were formed by the deposition of volcanic ballistics.
  • At least 4 new depressions aligned north west-south east are found at the center of the area where impact craters are densely packed.
  • Vents including 15m x 10m and 20m long show the entire length up to 100m.
  • From the distribution of impact craters, color of the volcanic ash and freshness of crater topography, the chain of volcanic vents mid-west on the Kagamiike crater-floor is considered to have formed by the volcanic activity starting around 10AM on 23rd

*For citing the pictures, please contact Yomiuri Shimbun.

Fig.1 Kagamiike and the Kagami-ike northern craters at Kusatsu-Shirane volcano. A chain of volcanic vents was found also on the Kagamiike crater-floor (lowest in the figure).
Fig.2 Chain of eruptive vents on the Kagamiike crater-floor. Left is close-up of fig.1. Right is picture taken from the east. Black arrows indicate small vents covered by snow. Snow avalanche is considered to have occurred just after the eruption.
（In association with Yomiuri Shimbun）

(Volcano Research Center: Setsuya Nakada)

29th January, 2018

Aerial Observation of Kusatsushirane (Motoshirane) volcano

Overview: After the eruption of Kusatsushirane volcano on 23rd January 2018, observation from a helicopter (air craft operated by Yomiuri Shimbun) was carried out in the afternoon of 28th January. Eruptive vents in chain (at least 6 of them) extending east-west at the north side of Kagami-ike northern crater were identified. And on their crater wall, the deposit (mainly consisting of volcanic ash, maximum thickness 1.5 m) covering the lodging timbers was also recognized.

  • Observed the Kagami-ike northern crater and its surrounding at Motoshirane volcano from a helicopter (Sirius, Yomiuri Shimbun) at 13:35-14:25 on 28th January. Condition of vents and deposit was observed.
  • Eruptive vents in chain (at least 7 of them) extending east-west, mainly at the north side of Kagami-ike north pond was found (Fig. 1).
  • Out of those, a small vent at the western side was about 15m×5m extending north-south and black deposit was observed inside (Fig. 2).
  •  At the crater wall on the Kagamiike northern vent, deposits cover lodged stems and branches, with upper most layers in grayish brown ash (Fig. 3). At the lower layer, brownish deposit exists, which is considered to be the former land surface. Therefore, upper layers above the timber are considered to be the deposits from this eruption (mainly volcanic ash, maximum thickness 1.5 m).
Fig.1 A chain of volcanic vents formed on the north and west side of Kagamiike northern crater, Motoshirane volcano.
Fig. 2 Close-up of a small volcanic vent (W, 15m×5 m) formed on the west side of the Kagamiike northern crater. The northern half is filled with black deposit. Some boulders that are considered to be deposited when the vent was formed, are scattered around the vent.
Fig. 3 Condition of the vent wall. Lodged stems and branches are concentrated at the bottom of the uppermost layer (maximum thickness 1.5 m). Between this and the lower brownish soil layer is considered to be the former land surface. (In association with Yomiuri Shimbun)

※  For citing the pictures, please contact Yomiuri Shimbun.

(Volcano Research Center: Fukashi Maeno)