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La Palma volcano (Spain) - Smithsonian / USGS Weekly Volcanic Activity Report for 24 November-30 November 2021 (Continuing Activity)

Ср, 24 ноя 2021, 06:00
The eruption at La Palma continued during 24-30 November, characterized by Strombolian explosions and lava fountaining/jetting from multiple existing and new vents, advancing and sometimes branching lava flows, and daily ash emissions. The eruption began on 19 September and had been active for 70 days by 28 November. Volcanic tremor levels were low, though during 28-29 November levels fluctuated and were sometimes intense.
Seismicity persisted at variable but elevated levels, with earthquake locations distributed at depths of 10-15 km and 30-40 km. Deeper seismicity decreased to low levels by 27 November while mid-level seismicity intensified through the week. The largest earthquake was a M 5 recorded at 0935 on 29 November at a depth of 36 km.

A M 4.2 earthquake at a depth of 13 km was the largest event at mid-levels since the eruption began.

Several vents in the main cone continued to effuse lava, eject tephra, and emit ash-and-gas plumes. Lava moved W through pre-existing lava channels, lava tubes, over older flows, and over new ground, increasing the flow field that consists of overlapping flows (numbered 1-11) and two lava deltas. During 23-25 November flows 4, 5, and 7 at the N end of the flow field continued to widen and advance, filling in gaps between the flows, and fed the N delta.
Flows 1, 2, and 9 minimally fed the S delta. There was also an increasing number of active flows on the flow field as lava overflowed some channel margins or broke out of tubes. At around 0900 on 25 November the lava effusion rate increased at main crater vents, and around 1100 two small E-W fissures opened less than 1 km S of the main cone.
The easternmost vent produced a fast-moving lava flow that traveled along the S margin of flow 10 and around the S side of Montaña Cogote. The flow advanced through the Las Manchas cemetery and inundated parts of a solar power plant; the newly covered areas were part of the exclusion zone and had already been evacuated. The flow rate slowed to about 25 m per hour and joined flow 11 by 26 November.
An overflow of lava SW of flow 3 produced a small branch oriented laterally the flow margin. Flow 7 widened during 26-27 November as it continued to be fed.

New vents opened on the NE flank of the main cone at around 0300 on 28 November, producing fluid lava flows that traveled N and NW through the Tacande area and crossed the LP-212 road. The opening of the new vents was followed by landslides on the NW flank of the cone. In a video taken at 1145 lava fountains rose from one of the vents while another ejected tephra.
Dense billowing ash plumes rose from the main crater. Video taken at 1050 on 29 November showed lava flows transporting large blocks downslope. Another video showed lava flowing at a rate of about 1 m per second.
By noon the vents in the main cone became notably less active and remained only intermittently active through 30 November. Several streams of lava from the new vents continued to advance NW and then W along older flows and split into two branches. One branch traveled through tubes and fed flows 4, 5, and 7 between Montaña de Todoque and Montaña de La Laguna and the other descended towards flow 8 (the most northern flow).
Flows inundated previously untouched forest and agricultural land. By 30 November the width of the flow field had grown to 3.35 km and lava covered an estimated 11.34 square kilometers. The number of people that had evacuated and were staying in hotels had increased to 537.

Gas and ash emissions again impacted island residents. Suspended ash and high concentrations of volcanic gases triggered a few air-quality alerts mostly affecting the W part of the island; authorities warned residents of some affected areas to stay indoors. Essential personnel were occasionally barred from entering the exclusion zones to irrigate crops and remove ash from streets and buildings.
Heavy rains during 25-26 November triggered warnings from authorities to stay away from steep slopes and drainages due to the possibility of lahars. Ash plumes rose as high as 4.8 km and drifted E during 24-26 November, and continued to deposit ash at La Palma airport. By 27 November winds had shifted and the ash at the airport had been removed, allowing it to open for the first time since 20 November.
Ash plumes rose 1.4-3.5 km and drifted SW and SSW during the rest of the week. Sulfur dioxide emissions continued an overall downward trend during 23-26 November, though heavy rain sometimes prevented ground-based measurements. The trend was broken on 27 and 28 November with values of 30,000-49,999 tons per day, characterized as “very high.” During 29-30 November emission values were “high” or between values of 1,000 and 29,999 tons per day.

Sources: Instituto Volcanológico de Canarias (INVOLCAN), Instituto Geográfico Nacional (IGN), Gobierno de Canaries
From: Global Volcanism Program, 2021. Report on La Palma. In: Mayberry, G (ed.), Weekly Volcanic Activity Report 24 November-30 November 2021. Smithsonian Institution and US Geological Survey.

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