SERNAGEOMIN reported that a notable change in seismicity at Cerro Hudson was characterized by an increase in the frequency and magnitude of volcano-tectonic (VT), hybrid (HB), and long-period (LP) signals during 1-15 December. Two swarms of VT earthquakes were recorded during 10-11 December, with the largest event, a local M 2.9, located 4.7 km ESE of the caldera’s center at a depth of 4.6 km. The largest of five HB signals was a local M 3.1, located 4 km ESE at a depth of 4.3 km. The earthquake locations suggested a relatively shallow source SE of the caldera. No deformation or surficial changes were observed. The Alert Level was raised to Yellow (second highest level on a four-color scale) on 22 December, based on the increased seismicity. ONEMI warned the communities of Aysén and Río Ibáñez, declaring a status of “Preventive Early Warning”, a level in between Green and Yellow.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)

HVO reported that a new eruption at Kīlauea began on 20 December, after almost a month of pre-eruptive activity that included a dike intrusion. An earthquake swarm on 30 November centered in the middle of the caldera was recorded followed by periods of increased seismicity in the upper East Rift Zone. Spikes in seismicity began on 2 December; at 1745 earthquakes intensified beneath the S part of the caldera; tiltmeters simultaneously recorded accelerated deformation, resulting in about 8 cm of caldera floor uplift. The data suggested that a small intrusion had a volume equivalent to the amount of lava erupted in just 1-2 hours from Fissure 8 during the 2018 eruption. On 3 December seismcity and deformation decreased to pre-intrusion levels.

On 17 December the number and duration of long-period seismic signals increased. An earthquake swarm and deformation were detected during the evening of 20 December. At about 2136 on 20 December an orange glow was evident in IR monitoring cameras, heralding a new eruption, and prompting HVO to raise the Volcano Alert Level to Warning and the Aviation Color Code to Red. Three fissures successively opened on the inner N, NW, and W walls of Halemaʻumaʻu Crater; lava flows quickly boiled away the water lake, creating a vigorous steam plume, before the lava ponded at the bottom. Minor lava fountaining (25 m high) from the fissures was visible, with the tallest fountains reaching 50 m at the N fissure. Occasional blasts originated from the ponded lava. A M 4.4 earthquake beneath the S flank was recorded at 2236.

A gas plume was seen rising from Halemaʻumaʻu Crater and drifting SW at 0215 on 21 December. Later that morning HVO lowered the Volcano Alert Level to Watch and the Aviation Color Code to Orange. The accumulating lava in the crater rose at a rate of several meters per hour. Sulfur dioxide plumes drifted NW. By the morning of 22 December, the surface of the lava lake was about 134 m above the bottom of the crater, or 487 m below the crater rim, and rising 1 m/hour. An estimated 10 million cubic meters of lava had been erupted so far. Sulfur dioxide emission rates remained high, at around 30,000 tonnes/day. Lava effusion stopped at the NW vent during 0730-0800, and, along with the W vent, was inundated by the lava lake sometime before noon.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)

PVMBG reported that the eruption at Lewotolo continued during 16-22 December. Gray-and-white ash plumes were visible daily, rising as high as 800 m above the summit. Strombolian explosions were visible most nights ejecting material 100-200 m above the summit crater. Rumbling was heard most days. The Alert Level was remained at 3 (on a scale of 1-4) and the public was warned to stay 4 km away from the summit crater.

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

BPPTKG reported that during 12-17 December white emissions from Merapi rose as high as 150 m above the summit. Rock avalanches traveled as far as 1.5 km down the Senowo drainage on the NW flank on 14 December. A comparison of photos taken on 11 and 15 December showed minor morphological changes in the summit area; drone video from 14 December revealed no new lava dome material in the summit crater. Seismic activity was less intense than the previous week. Electronic Distance Measurement (EDM) data continued to measure a distance shortening between points in the NW at a rate of 9 cm per day. The Alert Level remained at 3 (on a scale of 1-4).

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

GeoNet reported a warming trend of the crater lake water at Ruapehu, with a high temperature of 43 degrees Celsius. During an overflight to measure gas emissions the previous week, scientists observed that the lake was a uniform gray color (suggesting it is well mixed) and some water overflow at the lake’s outlet. Gas output had increased in response to the heating cycle; the amounts of carbon dioxide (CO₂) and sulfur gases (SO₂ and H2S) in the plume were the largest measured in the past two decades. Short-lived pulses of volcanic tremor were coincident with gas emissions. The Volcanic Alert Level was raised to 2 and the Aviation Color Code was raised to Yellow on 21 December.

Source: GeoNet

JMA reported nightly incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) during 14-21 December and that the sulfur dioxide emission rate remained high. Four explosions were recorded during 16-18 December. One of the explosions, at 1959 on 17 December, generated a plume that rose 3 km above the crater rim and ejected bombs 1.3-1.7 km away from the crater. Another explosion, at 0439 on 18 December, produced a plume that rose 1.8 km and ejected bombs 1-1.3 km away from the crater. The Alert Level remained at 3 (on a 5-level scale).

Source: Japan Meteorological Agency (JMA)

Based on satellite and wind model data, the Darwin VAAC reported that during 18-19 December ash plumes from Dukono rose to 2.1 km (7,000 ft) a.s.l. and drifted SE and E. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

Sources: Darwin Volcanic Ash Advisory Centre (VAAC), Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions during 11-12 and 15-17 December that sent ash plumes up to 3 km (10,000 ft) a.s.l. and drifted NE, SE, and S. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

INGV reported that strong activity at Etna’s Southeast Crater (SEC) included fountaining and lava flows on 21 December. Tremor amplitude had gradually increased on 20 December but weather conditions prevented visual observations. During the morning of the 21st Strombolian activity occurred at three vents. By 0800 tremor amplitude suddenly increased, and by 1000 lava fountaining from at least two vents was observed in thermal camera images, along with an eruption plume to 3 km (10,000 ft) a.s.l. [Correction: the eruption plume rose to 10 km (32,800 ft) a.s.l.] A lava flow emerged from the SW part of the cone, which had collapsed on 13 December, and traveled SW before branching W and E. A second flow from the NE side of the cone traveled E into the Valle del Bove. Lava fountaining ended around noon, with a simultaneous decrease in tremor amplitude. [Addition: An episode of lava fountaining occurred before sunrise on 22 December, producing lava flows that traveled SW, SE, and ENE.] During the morning of 22 December a few small phreatic explosions were visible in webcam images, likely generated from the interaction of snow and lava. The front of the active SW flow reached 2,500 m elevation. By 1741 both flows were cooling down and no longer advancing.

Source: Sezione di Catania - Osservatorio Etneo (INGV)

PVMBG reported that at 1826 on 19 December an ash plume from Ibu rose 400 m above the summit and drifted N. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay at least 2 km away from the active crater, and 3.5 km away on the N side.

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

KVERT reported that a thermal anomaly over Karymsky was visible during 11-12 and 17 December. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

KVERT reported that Strombolian and sometimes Vulcanian activity at Klyuchevskoy continued during 11-18 December and lava advanced down the Kozyrevsky drainage on the S flank. A large bright thermal anomaly was identified daily in satellite images. A steam-and-gas plume with some ash rose to 6 km (19,700 ft) a.s.l. and drifted 120 km NE on 13 December. The Aviation Color Code remined at Orange (the second highest level on a four-color scale).

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

JMA reduced the exclusion zone for Nishinoshima from a radius of 2.5 to 1.5 km around the summit crater on 18 December; eruptive activity ended in August. Fumarolic and high-temperature areas remained visible.

Source: Japan Meteorological Agency (JMA)

CENAPRED reported that each day during 16-22 December there were 112-231 steam-and-gas emissions from Popocatépetl, some of which contained minor amounts of ash. A gas, steam, and ash plume drifted SE on 22 December. The Alert Level remained at Yellow, Phase Two (middle level on a three-color scale).

Source: Centro Nacional de Prevencion de Desastres (CENAPRED)

IG reported that a high level of activity continued to be recorded at Reventador during 16-22 December; adverse weather conditions sometimes prevented visual conformation. Seismicity was characterized by 40-109 daily explosions, volcano-tectonic and harmonic tremor events, and long-period earthquakes as well as signals indicating emissions. Gas, steam, and ash plumes, observed sometimes multiple times a day with the webcam or reported by the Washington VAAC, rose as high as 1 km above the summit crater and drifted mainly NW and W. Crater incandescence and incandescent blocks rolling 600 m down the NE and S flanks were observed nightly. The 450-m-long lava flow on the NE flank remained active but did not advance.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN)

IG reported a high level of activity at Sangay during 16-22 December. Seismicity was characterized by 20-127 daily explosions, occasional harmonic tremor, long-period earthquakes, and signals indicating emissions. Weather clouds often prevented visual observations of the volcano, but the Washington VAAC and IG webcams recorded daily ash plumes that rose as high as 2.4 km above the summit and drifted mainly NW, W, and SW. Seismic signals signifying lahars were recorded during 16-18 December.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN)

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images during 11-18 December. On 22 December residents of Ust-Kamchatsk Village, 85 km SE, observed ash plumes rising to 8 km (26,200 ft) a.s.l. and drifting 42 km NE. The Aviation Color Code was raised to Red (the highest level on a four-color scale). Just over an hour later ash plumes rose 6.5-7.5 km (21,300-24,600 ft) a.s.l. and drifted 130 km E; the Aviation Color Code was lowered to Orange.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

JMA reported nighttime incandescence and intermittent eruptive activity at Suwanosejima’s Ontake Crater during 11-18 December. A total of five explosions were recorded, ejecting bombs up to 500 m away from the crater and producing gray-and-white plumes that rose 1.6 km above the crater rim. Ashfall was reported in Toshima village (4 km SSW). The Alert Level remained at 2 (on a 5-level scale).

Source: Japan Meteorological Agency (JMA)

POVI reported that four ash emissions at Villarrica were visible in webcam images on 16 December. SERNAGEOMIN stated that two ash pulses were associated with long-period (LP) events at 1146 and 1156 that same day; the first ash emission rose 160 m above the crater rim and drifted NW while the second rose 280 m and drifted 500 m NE. At 1716 on 17 December an ash emission associated with an LP event rose 720 m and drifted ESE. The Alert Level remained at Yellow, the second lowest level on a four-color scale. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the municipalities of Villarrica, Pucón (16 km N), Curarrehue, and the commune of Panguipulli, and the exclusion zone for the public of 500 m around the crater.

Sources: Proyecto Observación Villarrica Internet (POVI), Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI), Servicio Nacional de Geología y Minería (SERNAGEOMIN)