In Chile, OVDAS reported an explosion at Nevados de Chillan on November 18 at 19:17 local, at coordinates 36,863 S / 71,376 W and a depth of 1.2 km /, associated with an LP seismic signal. The plume has reached a height of 560 meters.
During the night, explosions, with incandescent projections were observed around the active crater. The extrusion of several lava flows on the NNE slope continues, with a very low rate of progression. The block flow traveled 700 meters from the crater towards NNE, covered half by another flow of lesser extent.
Pyroclastic flow deposits were observed in the SO, NW, N and NNE directions, respectively over 850, 670, 1680 and 440 m.
The crater zone changes morphologically: the crater Nicanor tends to grow on its SO edge, eroding the crater Arrau. NE side of the active crater, an emission focus is responsible for emission of gas and pyroclastic materials.
The technical alert level remains in Naranja.
ONEMI has published a new map of potentially at-risk areas.
Sources: Sernageomin / OVDAS, Onemi
The BPPTKG has produced a summary video of the magmatic activity of the Merapi in 2018-2019: phreatic eruptions, dome growth, block avalanches to Kali Gendol, and the latest explosions.
Kubah Lava Erupsi Gunung Merapi 2018-2019
The explosive behavior of Merapi has been explained in a recent article by Nature com. : "Hydrothermal alteration of andesitic lava domes can lead to explosive volcanic behavior."
" Dome-forming volcanoes are among the most hazardous volcanoes on Earth. Magmatic outgassing can be hindered if the permeability of a lava dome is reduced, promoting pore pressure augmentation and explosive behaviour. Laboratory data show that acid-sulphate alteration, common to volcanoes worldwide, can reduce the permeability on the sample lengthscale by up to four orders of magnitude and is the result of pore- and microfracture-filling mineral precipitation. Calculations using these data demonstrate that intense alteration can reduce the equivalent permeability of a dome by two orders of magnitude, which we show using numerical modelling to be sufficient to increase pore pressure. The fragmentation criterion shows that the predicted pore pressure increase is capable of fragmenting the majority of dome-forming materials, thus promoting explosive volcanism. It is crucial that hydrothermal alteration, which develops over months to years, is monitored at dome-forming volcanoes and is incorporated into real-time hazard assessments." (Heap, M.J., Troll, V.R., Kushnir, A.R.L. et al., Hydrothermal alteration of andesitic lava domes can lead to explosive volcanic behavior Nat Nat 10, 5063 (2019) doi: 10.1038 / s41467-019-13102-8)
The explosive behavior of the Merapi volcano appears to be caused by hydrothermal alteration, with cycles.
- The step of degassing the dome through open fractures.
- Alteration, sealing and pressurization phase.
- Explosion. The explosion is interpreted as a consequence of the increased pressure in the pores under the dome. Some fractures are reopened and new fractures are formed, allowing passive degassing after the explosion
Sources: BPPTKG and Nature comm. / Heap, M.J., Troll, V.R., Kushnir, A.R.L. et al. Hydrothermal alteration of andesitic lava domes can lead to explosive volcanic behavior. Nat. Commun. 10, 5063 (2019) doi: 10.1038 / s41467-019-13102-8
The swarm of earthquakes, in relation to tectonics, which began on Saturday, November 16th on the ridge of Reykjanes is decreasing.
Today, 18 November, 3 earthquakes have been detected in the region, all below M2.0. Yesterday, about 30 earthquakes> M3.0 were detected in the region. The most important earthquakes of the swarm were M4.5 at 4:17 pm on November 16th.
The swarm is located 45 km southwest of Reykjanes. Approximately 230 more minor earthquakes have been detected since the beginning of the swarm. IMO has received reports of earthquakes in the Reykjanes Peninsula, the Capital Region and Akranes.
Reykjanes Ridge - intensity and number of earthquakes at 16.11.2019 / 20.30 - IMO & characteristics of the seismic swarm between 03.11 and 18.11.2019 - Vedur.is
The earthquake swarm east of Askja, also in relation with tectonics, has decreased.
Sources: Vedur, is & the volcanologist Dave McGarvie