On 27 May AVO reported that seismicity at Great Sitkin was low following a 25 May explosion, and satellite images showed minor steaming and slightly elevated surface temperatures. The Aviation Color Code and the Volcano Alert Level were lowered to Yellow and Advisory, respectively. Seismicity remained low through 1 June; moderately elevated surface temperatures were detected during 29-30 May.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

The Darwin VAAC reported that on 25 May a diffuse ash plume from Anak Krakatau was visible in satellite images drifting SW at an altitude of 1.8 km (6,000 ft) a.s.l.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)

Satellite data and analysis indicated that the lava flows at Nyiragongo during 22-23 May were the result of a N-S trending dike that had intruded beneath the volcano and Goma, and likely extended beneath Lake Kivu. Though lava effusion ceased, intense seismicity continued afterwards and indicated the dike continued to be active, according to GeoRiskA. Ground cracking in the city and damage to buildings from earthquakes continued to be reported. On 27 May authorities mandated an evacuation of the at least 400,000 residents in higher risk areas (about 10 districts) according to news organizations. The total population of Goma is an estimated 670,000 people. Photos in news articles showed masses of people and cars jammed for kilometers on roads leading out of the city. During 28-29 May GeoRiskA reported that seismicity began to decrease and continued a downward trend at least through 1 June; both the seismic data and GPS data indicated that the dike was no longer propagating. A news article noted that residents had begun returning to their homes within a few days.

Humanitarian organizations noted that within five days after lava flow stopped nearly 700 children had been re-united with their families, and more than 200 were in foster care or other transitional facilities. More than 170 families continued to search for missing children. The eruption had destroyed 3,629 homes, 12 schools, and 3 health facilities. More than 20,000 people were displaced and 31 had died. Goma’s international airport remained closed, though one across the border in Rwanda was operating.

Sources: GeoRiskA, UN News Centre, SCK TV Dans Le Monde, European Commission - Directorate General for Humanitarian Aid and Civil Protection, Actualite.cd

AVO reported that an eruption at Semisopochnoi continued during 25 May-1 June. Steaming from the N crater at Mount Cerberus was visible in satellite images on 25 May. Radar data acquired between 15 and 27 May showed no morphological changes to the active vent. Tremor began to be recorded after AVO field engineers restored the satellite uplink to the seismic stations on 26 May. Field crews on 29 May observed low-level ash plumes rising to 2.4-3 km (8,000-10,000 ft) a.s.l., and small ash clouds drifting SW were visible in satellite images at around 0810 and 0920. Diffuse ash emissions were visible in satellite imagery at 1110. Strongly elevated surface temperatures were also identified in satellite data. Increased seismic tremor and accompanying low-level ash emissions began at 0945 on 30 May, with ash plumes drifting S at an altitude of 1.5 km (5,000 ft) a.s.l. at least through 1250. Elevated surface temperatures were detected during 30-31 May, likely from hot material on the crater floor. Seismic data showed low-level continuous tremor and occasional small discrete events. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

INETER reported that a series of 16 small explosions at Telica began at 0508 on 22 May, and produced ash-and-gas emissions that rose 250 m above the crater. Tephra from the plumes fell back down into the crater.

Source: Instituto Nicaragüense de Estudios Territoriales (INETER)

JMA reported that during 24-31 May incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was visible nightly. Very small eruptive events were occasionally recorded. 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)

Based on satellite and wind model data, the Darwin VAAC reported that during 25-27 and 29 May ash plumes from Dukono rose to 2.1 km (7,000 ft) a.s.l. and drifted N, NE, 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 21 and 23 May that sent ash plumes to 3.2 km (10,500 ft) a.s.l. and drifted NE and S. A thermal anomaly was identified in satellite images on 23 May. 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 almost daily episodes of Strombolian activity at Etna’s Southeast Crater (SEC) during 24-30 May continued the recent pattern of Strombolian explosions followed by lava flows to the SW and occasional lava fountains. Ash plumes were visible most days, rising to a maximum of 7 km (23,000 ft) a.s.l. Tephra was collected in Milo (10 km E) on 26 May and in Petrulli (12 km SE) on 30 May.

The first episode of the week began at 2100 on 24 May, intensified during 2235-2345, and ended at 0010 on 25 May. Ash emissions at SEC began 1020 on 25 May, producing a plume that rose to 4 km (13,100 ft) a.s.l. and drifted ENE. Explosions were recorded at 1820 and within 30 minutes Strombolian activity was visible. Activity intensified during 2025-2100 and ended at 2215. Two eruptive episodes were recorded on 26 May, with peaks at 0350 and 1300. An eruptive episode on 27 May was not visually well-documented due to inclement weather, though it reportedly intensified at 1450. Tephra fell in Giarre (17 km ESE), Milo, and Fornazzo (10 km ESE). Another episode began around 0830 on 28 May, intensified around 0900, and then ended at 0930; ashfall was reported in Giarre. Two more eruptive events were recorded that day: during 1740-1815 and a more powerful one during 2115-2305. The last episode of the week began at 0545 on 30 May and lasted for two hours.

Source: Sezione di Catania - Osservatorio Etneo (INGV)

The fissure eruption in the W part of the Krýsuvík-Trölladyngja volcanic system, close to Fagradalsfjall on the Reykjanes Peninsula, continued during 26 May-1 June. Cycles of lava fountaining followed by no activity persisted at the fifth vent. Lava fountains rose a few hundred meters above the vent and lava advanced in the Nátthaga and Geldingadalur valleys. Lava in Nátthaga continued to get closer to Highway 427 (Suðurstrandarvegur) to the S, and buried fiber optic communication cables. Seismic activity had been decreasing; during 21-28 May there were about 90 earthquakes, compared to the 200 events recorded the previous week. According to a news article, an estimated 31 hectares of vegetation had been scorched by fires set by lava and hot ejected material since early May. The Aviation Color Code remained at Orange due to the lack of ash and tephra emissions, though IMO warned of the potential for lapilli and scoria fallout within a 650 m radius of the active vent. Authorities warned of increased gas emissions hazards.

Sources: Icelandic Meteorological Office (IMO), Icelandic National Broadcasting Service (RUV), Icelandic National Broadcasting Service (RUV)

On 27 May AVO changed the Aviation Color Code and Volcano Alert Level for Gareloi to Green and Normal, respectively, reflecting that communication with seismic stations had been re-established, allowing for the location of earthquakes and detection of unrest.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

KVERT reported that a thermal anomaly over Karymsky was visible in satellite images on 22 and 24 May. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

PVMBG reported that at 0614 on 31 May an ash plume from Kerinci rose 700 m above the summit and drifted NW, based on information from a ground observer. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 3-km exclusion zone.

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

On 27 May HVO reported that Kīlauea was no longer erupting; the Aviation Color Code and the Volcano Alert Level were lowered to Yellow and Advisory, respectively. A decreasing rate of lava entering the lake caused the area of the active lava lake to shrink to two small ponds by 11 May. Lava had stopped flowing into the lake sometimes during 11-13 May, and it was completely crusted over by 20 May. Weak inflation and an increase in shallow volcano tectonic earthquakes at the summit that began on 11 May also suggested that magma was staying at depth.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)

PVMBG reported that white-and-gray plumes from Lewotolok rose as high as 1 km and drifted W and E during 27-28 and 30-31 May. Rumbling was sometimes heard. Crater incandescence was visible on 31 May. 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 that the lava dome just below Merapi’s SW rim and the lava dome in the summit crater both continued to be active during 21-27 May. The SW rim lava-dome volume was an estimated 1.265 million cubic meters, with a growth rate of about 11,600 cubic meters per day, and continued to shed material down the flank. A total of 15 pyroclastic flows traveled a maximum of 2 km down the SW flank. Incandescent avalanches, recorded 70 times, traveled as far as 1.8 km down the SW flank and once went 800 m SE. The summit lava dome had not changed since observations the previous week. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 5 km away from the summit.

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

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images during 21-28 May. 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 47 explosions at Suwanosejima's Ontake Crater produced eruption plumes that rose as high as 2.1 km above the crater rim during 21-28 May. Large volcanic bombs were ejected 700 m from the crater. Ashfall was reported in Toshima village (4 km SSW). Crater incandescence was visible nightly. The Alert Level remained at 2 and the public was warned to stay 1 km away from the crater.

Source: Japan Meteorological Agency (JMA)

On 27 May the Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that seismic data and recent visual observations at Yasur confirmed ongoing explosions and gas-and-ash emissions. The Alert Level remained at 2 (on a scale of 0-4). VMGD reminded residents and tourists that hazardous areas were near and around the volcanic crater, within a 600-m-radius exclusion zone, and that volcanic ash and gas could reach areas impacted by trade winds.

Source: Vanuatu Meteorology and Geohazards Department (VMGD)