The eruption at La Palma continued during 21-28 September, characterized by Strombolian explosions, lava fountaining from multiple vents, advancing lava flows, and sometimes dense, daily ash emissions. A strong increase in tremor amplitude during the afternoon of 21 September was coincident with intensifying Strombolian activity. Explosive activity again increased on 22 September and dense plumes with abundant amounts of ash rose 3-4.6 km (10,000-15,000 ft) a.s.l. and caused ashfall in areas downwind; ash deposits were 3 cm thick in an unspecified area 1 km from the vents. The main lava flow advanced W towards the coast. Ash emissions significantly increased on 23 September with plumes rising as high as 5 km (16,400 ft) a.s.l. A series of powerful explosions began at 1720 and shock waves could be seen propagating through the emission plumes. Vigorous lava fountaining was continuous. Volcanic tremor amplitude was high and variable, peaking at 1500 on 24 September with the highest values since the eruption started. The peak occurred just before two new vents opened on the flank of the main cone, and then notably decreased afterwards, but remained at high levels. Lava from the new vents rapidly traveled more than 1 km downslope, covering older flows, before slowing to 60-80 meters per hour. According to a news report, the explosions ejected tephra outside of the exclusion zone. An evacuation order was issued in the early afternoon for Tajuya, Tacande de Abajo, and part of Tacande de Arriba, affecting 300-400 people. Three airlines suspended flights to La Palma. The lava flow field had expanded to 1.9 square kilometers, destroyed more than 420 buildings, and covered 15.2 km of roads.

Tremor amplitude decreased around noon on 25 September, along with the intensity of the Strombolian explosions. During 25-26 September ash fell in nearby municipalities and as far as the E coast of the island. On 26 September the PEVOLCA steering committee recommended that residents who had evacuated two days earlier could return. The report described two main lava flows, with a highly fluid northern flow and a southern flow that was 2.5 km long. Sulfur dioxide emissions remained significant with an average rate of 25,000 tons per day, and ash plumes rose as high as 3 km above the vents. Lava continued to advance and flowed through Todoque, crossing the LP-213 road, just W of the main part of the town, at around 1900. The flow was 600 m across at the widest part and the leading edge was 4-6 m tall. Lava fountaining and low-intensity Strombolian explosions persisted. Copernicus EMS estimated that the lava covered 2.37 square kilometers, had destroyed 513 houses, and covered 18.9 km of roads. Multiple lava fountains feeding flows were visible on 27 September though the activity waned for a period of about eight hours. By the evening activity had resumed and low-intensity Strombolian explosions were visible.

Beginning at 0245 on 28 September lava fountains fed a new high-temperature, fast-moving flow that descended on top of older flank flows. The leading edge of the main flow continued to advance W and covered banana greenhouses, burning the plastic and igniting a storage of fertilizer resulting in small explosions and a brown odorous plume. About 140 more structures were covered by flows. In preparation for a possible ocean entry, authorities recommended that residents within a 5 km radius of the coastline keep their doors and windows closed, to stay away from windows in case they break, and to cover faces and skin in case of ashfall. Dense ash-and-gas plumes continued to rise from the main vents, as high as 5 km; the rising plume created gravity waves that looked like ripples moving away from the top of the plume. Late in the day lava reached the coastal area, descended a 100-m-high sea cliff, and by 2302 reached the ocean at Playa de los Guirres. Black-and-white plumes rose from where the lava contacted the water.

Sources: Instituto Geográfico Nacional (IGN), Instituto Volcanológico de Canarias (INVOLCAN), Gobierno de Canaries, EL PAÍS, CNN, EL PAÍS, Toulouse Volcanic Ash Advisory Centre (VAAC), Copernicus Emergency Management Service

OVG reported that lava had returned to Nyiragongo’s summit crater based on a 29 September Sentinel satellite image.

Source: Observatoire Volcanologique de Goma (OVG)

JMA reported that incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was visible on most nights during 20-27 September. The trend of inflation first detected on 13 September had begun to slow down by 21 September. The sulfur dioxide emission rate was high at 2,600 tons per day on 22 September. An eruptive event at 0110 on 23 September and two more during 24-27 September produced plumes that rose 1.1 km above the crater rim. The Alert Level remained at 3 (on a 5-level scale), and residents were warned to stay 2 km away from the crater.

Source: Japan Meteorological Agency (JMA)

According to volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, explosions on 20 September produced ash plumes that rose as high as 1.7 km (5,600 ft) a.s.l. and drifted SE. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

INSIVUMEH reported that during the night of 21-22 September a possible lava flow had traveled 400 m down Fuego’s Ceniza drainage on the SSW flank. Ash rose along the flow forming a curtain that extended above the summit; ash fell in communities to the W and SW. Explosions at a rate of 6-11 per hour produced ash plumes that rose as high as 800 m above the summit and drifted W and SW.

INSIVUMEH and CONRED reported that activity significantly increased on 23 September. Seismic activity intensified during the early morning and Strombolian activity at the summit was visible. Incandescent material was ejected 100-300 m high. Lava flows traveled 1 km down the Ceniza (SSW) and Trinidad (S) drainages, and sent block-and-ash flows down the Ceniza, Trinidad, Taniluyá, Las Lajas, and Santa Teresa (W) drainages to vegetated areas. Shock waves were detected within a 10 km radius. At 0540 a pyroclastic flow traveled 4-6 km down the Ceniza drainage, reaching the base of the volcano. According to CONRED a pyroclastic flow descended the Ceniza and Trinidad drainages 2-4 km. Explosions generated ash plumes that rose as high as 2.3 km above the summit and drifted 30 km W and SW. The activity began to decline around noon the next day, based on seismicity, acoustic data, and field observations. A few hours later RSAM data suggested that the period of elevated activity had ended after about 32 hours from the onset. Lava flows were no longer active by 25 September.

During 24-28 September there were that 6-12 explosions per hour generating ash plumes as high as 1.1 km above the crater rim and shock waves that often rattled buildings within 10 km of the volcano. Ash plumes mostly drifted as far as 15 km W and SW, causing daily ashfall in several areas downwind, including Morelia (9 km SW), Panimaché I and II (8 km SW), Santa Sofía (12 km SW), Finca Palo Verde, and San Pedro Yepocapa (8 km NW). Block avalanches descended the Ceniza (SSW), Seca (W), Trinidad (S), Taniluyá (SW), Las Lajas (SE), and Honda drainages, often reaching vegetated areas. Explosions ejected incandescent material 100-300 m above the summit on most days.

Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH), Coordinadora Nacional para la Reducción de Desastres (CONRED)

AVO reported that lava effusion continued at Great Sitkin during 22-28 September, though weather clouds sometimes prevented webcam and satellite views. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion. By 24 September the dome had overtopped the S and W crater rims and flowed 305 m down the S flank and 195 m down the W flank. The dome was about 25 m thick and had grown to 1,170 m E to W and 925 m N to S in dimension. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

KVERT reported that a thermal anomaly over Karymsky was identified in satellite images during 16-18 and 22 September. Ash plumes rose as high as 4.5 km (14,800 ft) a.s.l. and drifted 180 km E during 16, 18-19, and 22 September. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

AVO reported that beginning at 1730 on 23 September strong winds in the vicinity of Katmai and the Valley of Ten Thousand Smokes blew unconsolidated ash SE towards Kodiak Island at an altitude up to 1.5 km (5,000 ft) a.s.l. The ash was originally deposited during the Novarupta eruption in 1912. The Volcano Alert Level remained at Normal and the Aviation Color Code remained at Green.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

KVERT reported that on 29 September high winds caused unconsolidated ash from Klyuchevskoy’s flanks to form plumes that rose to 3-5 km (9,800-16,400 ft) a.s.l. and drifted 75 km E. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale).

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

Based on analyses of satellite imagery and wind model data, the Darwin VAAC reported that during 24-25 September three ash plumes from Langila rose to 2.1 km (7,000 ft) a.s.l. and drifted W and NW.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)

PVMBG reported that the eruption at Lewotolok continued during 21-28 September. White-and-gray plumes rose as high as 700 m above the summit and drifted NW, W, and SW. Rumbling sounds were reported almost daily. The Alert Level remained at 3 (on a scale of 1-4) and the public was warned to stay 3 km away from the summit crater.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

BPPTKG reported minor morphological changes to Merapi’s SW lava dome, located just below the SW rim and in the summit crater, and no changes to the summit crater dome during 17-23 September. The SW dome had an estimated volume of 1.6 million cubic meters and the summit lava dome had an estimated volume of 2.85 million cubic meters. As many as 141 lava avalanches traveled a maximum of 2 km SW. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-5 km away from the summit based on location.

Source: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG)

AVO reported that seismicity at Pavlof remained elevated during 21-28 September. Daily short-lived explosions from a vent on the upper SE flank were detected in seismic and infrasound data. Low-level ash emissions were visible in webcam images rising possibly several hundred meters above the summit during 21-23 September. Steam emissions rose from the vent during 24-25 September. The Volcano Alert Level and Aviation Color Code remained at Watch and Orange, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

GeoNet reported that a heating cycle at Ruapehu’s summit Crater Lake had ended. During the previous two months the temperature of the water increased from 20 degrees Celsius to a peak of 39.5 degrees on 4 September, and then decreased to 28 degrees. During the cycle the color of the lake changed from a blue-green color to a darker gray, reflecting the disturbed lake floor sediments suspended in the water from the influx of hot fluids. The key monitoring parameters of water level and temperature, seismic activity, and tremor levels, were all within normal ranges. The Volcanic Alert Level remained at 1 (minor volcanic unrest) and the Aviation Color Code remained at Green.

Source: GeoNet

INSIVUMEH reported that almost daily ash plumes from Santa Maria’s Santiaguito lava-dome complex rose 500-900 m and drifted W and SW during 19-27 September, depositing ash on the flanks. Extrusion continued at the summit dome complex, mainly from the W part of the dome. Avalanches produced by the active dome were sometimes incandescent and predominantly descended the W flank, though some also traveled S and SW. The avalanches often reached vegetated areas on the flanks.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 22-28 September. Seismicity remained elevated; daily explosions were recorded by seismic and infrasound networks. The frequency and intensity of ash emissions decreased during 21-22 September with occasional discrete ash clouds drifted W at altitudes of 3-4.6 km (10,000-15,000 ft) a.s.l. Sulfur dioxide plumes also drifted W. Occasional low-level ash emissions drifted NW, W, and SE during 22-26 September. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images during 17-24 September. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

JMA reported that the number of explosions per day at Suwanosejima's Ontake Crater had increased on 16 September and remained elevated through 27 September. A total of 105 explosions were recorded during 20-27 September. Eruption plumes mainly rose as high as 2.9 km above the crater rim and material was ejected as far as 800 m away from the crater. Ashfall was reported in Toshima village (4 km SSW). Notably, an explosion at 2349 on 20 September ejected material as far as 1.2 km SE. At 0711 on 26 September an eruptive event produced a plume that rose 5.4 km; weather clouds prevented confirmation of ejected bombs, but a large amount of ash fell in Toshima village. The Alert Level remained at 3 and the public was warned to stay 2 km away from the crater.

Source: Japan Meteorological Agency (JMA)

PVMBG reported that during 21-27 September white gas-and-steam plumes rose as high as 400 m above the rim of Tengger Caldera’s Bromo cone and drifted SW, W, and NW. White-and-gray plumes rose as high as 500 m during 22-23 September. A weak thermal anomaly was visible in Sentinel-2 infrared satellite images on 22 and 27 September. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to stay outside of a 1-km radius of the crater.

Sources: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Sentinel Hub

On 27 September GeoNet reported results from an overflight of Whakaari/White Island the previous week. Gas measurements showed that sulfur dioxide emissions had increased to 680 tons per day from 450 tons per day recorded in mid-August, continuing the trend of an increasing emission rate noted over the past few months. The gas data suggested magma input deeper in the system. Temperatures in the main vent area notably decreased to 189 degrees Celsius from July and August measurements of 650 degrees, possibly indicating cooling caused by groundwater infiltration. Minor ash deposits from recent emissions were visible around the active vents. Seismicity was characterized by low levels of volcanic tremor and occasional low-frequency volcanic earthquakes. Subsidence continued to be measured by satellite. The Volcanic Alert Level remained at 2 and the Aviation Color Code remained at Yellow.

Source: GeoNet