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Wednesday, September 22, 2021

The lava advanced at 4 meters per hour and last night it travelled only 15 meters

La Palma volcano Edge of lava estimated by ACO (1)

The PEVOLCA Steering Committee, which was attended by the Minister of the Interior, Fernando Grande-Marlaska and the President of the Canary Islands, Ángel Victor Torres, insisted on prevention as a security measure, since the La Palma volcano is alive and the island continues in an emergency situation, at red alert. Currently the lava advances at 4 meters per hour and last night it only travelled 15 meters. For scientists it is not feasible to redirect the lava and no action can be taken in this regard. [Did somebody try?]

The president of the Canary Islands, Ángel Víctor Torres, announced today that evacuated people who are in the shelter will be transferred to a hotel in Fuencaliente during the day, while people with reduced mobility will go to a social health centre. The intention of the authorities is to keep the shelter only as the first point in case of new evictions and to continue studying the housing alternatives for people staying in family homes.

The authorities recalled the need to let the emergency services work and stay outside the exclusion radius of 2.5 kilometres from the emission centres (vents) recommended by scientists to minimize the risk of impact from pyroclasts and exposure to gases of the volcano. It is also necessary to stay away from lava flows in the event of possible landslides and high temperatures, in addition to taking extreme precautions against falling ash.

The affected area currently covers 140.44 hectares, with a front of 600 meters. The technical director of PEVOLCA, Miguel Ángel Morcuende, stated that the volcano is still active, releasing lava, and the two flows continue to advance, but very slowly, due to the increase in viscosity and because it is filling in the natural holes of the terrain that is to be found in its path. Mathematical models indicate that it will continue to advance, but it cannot be guaranteed that it will reach the sea.

Morcuende explained that there is only one fissure, with 9 vents or emission centres, although not all are active. There has been a small movement of the lava that was standing in the southern area during the night, but minimal and there is no variation from the previous night. Last night there were several explosive episodes that may continue, although the deformity has not grown and remains at 28 centimetres. According to Morcuende, it is a time of mini stability, but is not known how long it can last.

Regarding the measurements of sulphur dioxide, he indicated that they do not reflect a danger to human health. The plume is at 3,000 meters of altitude. 

Scientific Comittee

The report of the Scientific Committee indicates that the eruption continues to show the same fissure eruptive style, with a strombolian mechanism, in a fissure in a NW-SE direction. Yesterday the main broadcasting centre had a phase of greater explosiveness that intensified at 7:00 p.m. (local time), reached its maximum at 9:00 p.m. and ended coinciding with the partial collapse of the upper part of the cone today at 2:00 a.m. local). In the last hours, a decrease in the average advance speed of the front of the lava flow has been observed to values ​​of 4 m / h. continuing its advance towards the sea.

It reaches thicknesses between 8 and 15 m. Seismicity continues at low levels. Today at 01:25 (local time) an earthquake of magnitude 2.2 mbLg, felt with intensity II, was located. The estimate of the emission rate of sulphur dioxide (SO2) into the atmosphere by this eruptive process during yesterday was between 6,140 and 11,500 tons per day. These values, although correctly measured, are underestimated by the large dimension of the sulphur dioxide plume observed by satellite. The emission of materials reaches 3,000 m according to the Toulouse VAAC.

The volcanic tremor signal shows a tendency to decrease in amplitude at seismic stations, probably due to the concentration of strombolian activity in a smaller number of centres. Likewise, it is found that the deformations have decreased their speed, showing relative stability in the last 12 hours. The deformation measured by the INSAR technique shows an average cumulative maximum of 28 cm.

Regarding meteorological information, the anticyclonic situation continues, with winds from the northeast from the surface up to 3000 meters, with intensities around 20 - 30 km / h (decreasing with height). On the west slope affected by the eruption, the breeze continues to predominate, that is, westerly winds during the day and downward mountain winds at night. The most significant thing is the turn of the wind from north / northeast to west increasing its intensity at this level from 5 km / h to 10-15 km / h, during the next morning at the level of 700 hPa (3000 meters approx.). This factor will influence the movement of ash to the east of La Palma. It is ruled out that any precipitations registered during the next 24 hours are acidic. 

Work is continuing on the numerical modelling of the extent of lava flows and the monitoring of the advance rate of lava flows and their extent. In addition, the daily monitoring of the emission of sulphur dioxide (SO2) from the eruptive foci is continued by means of remote optical sensors mounted on helicopters and the chemical composition of the plume by means of multigas sensors. Ash sampling and washing is done regularly. Field inspections and drone observations are underway.

It is possible that explosive episodes such as those that occurred yesterday (09/21) will be repeated. Given the large thicknesses of the lava flow observed in some points, collapses of its face can occur which, in steeper areas, can lead to the formation of large fragments of lava flow, which can detach from the face of the flow, suddenly reaching distances of several meters from the pouring face, depending on the topography. Also in steep areas, small pyroclastic flows can occur.

If the lava flows reach the coast, the scientists warn that the interaction of the sea with the lava could generate columns of water vapor with acid gases, detachment of the lava front, and the emission of fragments could be produced in the vicinity of the contact (fragmentation snapshot and emission of ballistic fragments). In this sense, the continuous monitoring of the activity has been reinforced and any significant changes observed will be communicated.