After an involuntary interruption of a few days due to computer problems, I slowly resume the blog, with partial information gleaned from the smartphone.
Experts have reported a recent change in the composition of volcanic ash emitted by Nishinoshima.
The magma seems to come from a greater depth, and future developments could include a collapse of the central cone, leading to subsidence of the whole island, and a possible tsunami.
Nishinoshima - heavy ash emissions have stopped, leaving a huge crater - photo Japan Coast Guards 05.09.2020
Volcanic ash from Nishinoshima collected in July 2020, when the island was in a violent eruption, shows how the magma was fractured into irregular shapes. (Provided by the Earthquake Research Institute of the University of Tokyo)
The large volumes of lava emitted made the island grow by 40%, increasing it from 2.89 km² in May 2019 to 4.1 km² in August 2020, based on satellite images.
There was also a change in the mode of eruption. Nishinoshima was only emitting lava until June, but began discharging large volumes of ash in late July, covering the entire island under several meters of this brown ash. JMA analysis of this ash in July shows that its silica dioxide content has dropped from 60 to 55%. The magnesium and calcium content has increased, resulting in a greater density of magma.
Sources: Japan Coast guards, the Earthquake Research Institute of the University of Tokyo & Asahi Shimbun
Nishinoshima - Fumaroles in the crater / which remains very hot on the IR image - photos Japan Coast Guards 05.09.2020
Insivumeh reports in its special September 11 bulletin that the effusive activity of Fuego has been on the increase since the 5th of the month.
Extrusion does not happen at a constant rate; the length of the lava flow in the Ceniza barranca varies from 100 to 650 meters approximately - the last daily bulletin indicates it at a length of 200 meters -, and the avalanches generated by the flow also affect the barrancas Trinidad and Tanilyua.
During the past week, an average of 10 loud explosions in 24 hours was recorded; they are interspersed with degassing intervals of between 10 and 30 minutes, with a peak on September 10 lasting 70 minutes.
Fuego - lava flow in the Ceniza barranca on September 10 (Landsat 8 image) and September 11 (webcam) - Doc. Insivumeh
Satellite data showed discoloration of the water around the Kavachi submarine volcano, possibly in early September; on September 7, discolored plumes in the water were visible east of the submarine cone. (Copernicus)
Named after a sea god of the Gatokae and Vangunu peoples, Kavachi is one of the most active underwater volcanoes in the Southwest Pacific, located in the Solomon Islands south of Vangunu Island about 30 km north of the Indo-Australian plate subduction site under the Pacific plate. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this basaltic to andesitic underwater volcano has produced ephemeral islands up to 1 km long on several occasions since its first recorded eruption in 1939.
Sources : Global Volcanism Program / Copernicus
Map of the Solomon Islands, with the main tectonic characteristics and the position of the Kavachi and Simbo volcanoes - Doc. Research gate
The National Service of Geology and Mines (Sernageomin), through its National Volcanic Monitoring Network (RNVV), has determined that since August 28, remarkable seismicity has been reported with maximum magnitudes of 5.4 in the Bransfield Strait, Chilean Antarctic territory, more precisely near the Orca seamount, considered to be an active volcanic center.
This seismic swarm is mainly dominated by events attributed to tectonic processes, with the appearance of some signs that could indicate the involvement of fluids in the upper part of the crust.
To be continued.
Source: Sernageomin / La Tercera