The isolated Semisopochnoi volcano occupies the largest and youngest volcanic island in the Western Aleutians. The volcano is dominated by an 8 km diameter caldera that contains a small lake and a number of post-caldera cones and craters. The age of the caldera is not known with certainty, but it is probably the beginning of the Holocene.
Prior to 2018, the previous known eruption of Semisopochnoi occurred in 1987, likely from Sugarloaf Peak on the island's south coast, but details are lacking. Mount Cerberus, a cluster of three-pointed cones in the southwestern part of the caldera, is another young and prominent landform after the caldera.
For much of the past week, low level ash emissions continued at Semisopochnoi. The plumes generally drifted south at elevations of about 10,000 feet a.m.s.l. for distances up to 100 km in length. SO2 emissions were also observed on Thursday, April 22, 2021.
The eruptive activity at Semisopochnoi has gradually increased over the past 24 hours. Satellite views of the volcano show a continuous plume extending 80 km to the south at about 2,450 meters a.m.s.l. A regional infrasound network has detected this increase in activity. Aviation color code and alert level remain at ORANGE / WATCH; however, AVO will continue to monitor activity with satellite and regional infrasound data.
Semisopochnoi - North Creberus plume & ash deposits to the south on 22.04.2021 / 22:12 UTC - Doc. AVO / Dietterich Anna / Planet sat.
Sinabung volcano was clearly visible on April 23 until it was covered in fog. The main crater is white smoke 50 to 300 meters from the summit.
Thanks to seismographic recordings of April 23, 2021, it was recorded:
- 1 eruption earthquake
- 106 collapse / avalanche earthquake
- 4 blast / emission earthquakes
- 8 low frequency earthquakes
- 12 hybrid / multiphase earthquakes
- 1 deep volcanic earthquake
- 1 deep tectonic earthquake
Activity level remains at 3 / siaga. Communities and visitors / tourists should not conduct activities in villages that have been moved, as well as location within a radial radius of 3 km from the summit of Mount Sinabung , as well as a sector radius of 5 km for the south-eastern sector, and 4 km for the east-north sector.
Sources : PVMBG, Magma Indonesia
The Anak Krakatau, in activity level 2 / waspada, can be discovered on April 22, topped by a beautiful plume of gas / steam.
The PVMBG reports for April 22 a seismicity characterized by:
- 6 blast / emission earthquakes, with an amplitude of 5 to 15 mm and the earthquake lasted 20 to 58 seconds.
- 2 shallow volcanic earthquakes, with an amplitude of 4 to 8 mm and the duration of the earthquake was 8 to 15 seconds.
- 1 deep volcanic earthquake with an amplitude of 33 mm, S-P 3.2 seconds and the duration of the earthquake was 15 seconds.
- 1 continuous tremor episode with an amplitude of 1-8 mm, dominating 1 m
Sources: PVMBG, Magma Indonesia, Mirova
Anak Krakatau - 04.22.2021 / 03:29 - Sentinel-2 bands 12,11,8A and Modis thermal volcanic activity - Doc. Mirova
The weather conditions and the observation of the eruption remain very poor at Piton de la Fournaise , for a few days.
The eruption continues at the level of the two cones at a relatively stable level for several days, as indicated by the intensity of the tremor.
Over the last 24 hours, 10 superficial volcano-tectonic earthquakes (between sea level and the surface) have been recorded under the summit craters.
The CO2 fluxes in the soil are still increasing both in the far field (Plaine des Cafres and Plaine des Palmistes) and in the near field (Gîte du volcan). Averaged over the past few days, no significant trend can be seen in the deformations of the building (neither in deflation nor in inflation). This could suggest a deep flow of magma entering the reservoir that feeds the eruptive site.