On 9 May the intermittent eruption of lava in Leilani Estates in the lower East Rift Zone (ERZ) of Kīlauea continued. In the northeast part of the area, fissure 15 extended across Poihiki Road, generating a pāhoehoe flow about 20 m (66 ft) long. In the summit caldera, steady lowering of the Overlook Crater lava lake within Halemaʻumaʻu crater raised the potential for steam-driven explosions if the lava column dropped to the groundwater level and allowed water into the conduit. On 10 and 11 May, little new extrusive activity was noted from the ERZ fissures, though there were continued earthquakes, ground deformation, and considerable gas discharge. Tiltmeters recorded ongoing deflation and the Overlook crater lava level continued to drop.

Fissure 16 opened at 0645 on 12 May near the end of Hinalo Road. It produced a lava flow that traveled about 230 m before stalling around 1430. An area that had been actively steaming developed into fissure 17, reported at 1800 just east of fissure 16, and was actively spattering and degassing. At the summit, rockfalls from the steep walls into Overlook crater generated intermittent small steam-and-ash clouds throughout the day.

Lava eruptions continued on 13 May along the lower ERZ. Aerial observations showed that a new outbreak in the early morning about 900 m NE of the end of Hinalo Street and 900 m S of Highway 132 was several hundred yards long and ejected spatter along with a slow-moving lava flow. By late in the day this activity from fissure 17 was dominated by lava fountaining, explosions that sent spatter bombs to 100 m into the air, and several advancing lava flow lobes moving generally NE; as of 1900 one lobe was 2 m thick and advancing roughly parallel to Highway 132. Steady, vigorous plumes of steam and occasionally minor amounts of ash rose from the Overlook vent and drifted downwind to the SW. Later in the day, ash clouds rose up to 650 m (2,000 ft) above the vent. Several strong earthquakes shook the Hawaiian Volcano Observatory and the surrounding area overnight.

Activity on the morning of 14 May in the lower ERZ was dominated by lava fountaining, explosions of spatter more than 30 m (100 ft) into the air, and an advancing flow from fissure 17 at the NE end of the fissure system. As of 0630, the fissure 17 flow had traveled about 1.6 km roughly ESE parallel to the rift zone. Fissure 18 was weakly active. A 19th fissure spotted around 0800 just NE of Pohoiki Road and N of Hinalo Street produced a sluggish lava flow. Volcanic gas emissions remained elevated throughout the area downwind of the vents. Deflationary tilt at the summit continued and seismicity remained elevated.

On the morning of 15 May activity remained concentrated at fissure 17. The lava flow had advanced about 380 m since 1430 on 14 May. At 0645 the flow was nearly 2.5 km long. However, the advance of the flow had slowed significantly since that afternoon. Also in the morning a new fissure (20) located near fissure 18 produced two small pads of lava. Ash emission from the Overlook crater increased compared to previous days. Although varying in intensity, at times the plume contained enough ash to be gray in color. Variable pulses sent the cloud to an estimated 1-1.3 km (3-4,000 ft) above the ground. The ash cloud drifted generally W and SW from the summit and ash fell in the Ka'u Desert. On 15 May the Aviation Color Code was raised from Orange to Red and the Volcano Alert Level remained at Warning.

Sources: US Geological Survey Hawaiian Volcano Observatory (HVO), Hawaii Emergency Management Agency, Hawaii County Civil Defense Agency

PVMBG reported that an explosive eruption occurred at 0740 on 11 May. The eruption began with a small roar and vibrations that were felt at the observation post for 10 minutes. The eruption plume rose to 5.5 km (18,000 ft) above the peak. There was no seismic precursor and no seismic activity continued after the event. PVMBG did not change the alert level from Green/Normal; they interpreted the event as a minor eruption triggered by the accumulation of volcanic gases unlikely to be followed by further eruptions.

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

On 4 May, the Icelandic Met Office reduced the Aviation Color Code at Öræfajökull from Yellow to Green due to signs of reduced activity. Since September 2017 there has been less earthquake activity, stable hydrological and geochemical measurements, and reduced geothermal heat output. There has been possible minor ongoing inflation, but no signs of an imminent eruption.

Source: Icelandic Meteorological Office (IMO)

OVPF reported that the eruption at Piton de la Fournaise, which began on 27 April from fissures at Rivals Crater, continued through 15 May. Field reconnaissance on 10 May revealed that activity was focused on the main cone, with some activity from a second cone that was ejecting material 10-20 m high. Over the next two days the crater of the main cone narrowed and lava projections at both cones became rare. Lava flows during this time were often confined to tubes, with some breakouts at the change in slope below Piton de Bert, about 3 km from the active cone. Burning vegetation as a result of the breakouts was visible on and at the foot of the rampart. Based on satellite data when surface flows were visible, lava emission rates were estimated to be about 1-2 cubic meters/second. Tremor intensity fluctuated over the week, with a sharp increase during 0500 and 0900 on 15 May.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPF)

Based on a VONA from PVMBG, on 9 May a gas emission was observed at 1807 from Sangeang Api that rose to 4,150 m (13,000 ft) a.s.l. and drifted west. On 9 May the Aviation Color Code was changed from unassigned to Yellow.

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

JMA reported that during 7-11 May there were 12 events, three of which were explosions, at Minamidake crater (at Aira caldera’s Sakurajima volcano). Tephra was ejected as far as 700 m from the crater, and ash plumes rose as high as 2.8 km (9,200 ft) above the crater rim. The Alert Level remained at 3 (on a 5-level scale).

Source: Japan Meteorological Agency (JMA)

Based on analyses of satellite imagery and model data, the Darwin VAAC reported that on 11 May at 0900 an ash plume from Bagana rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted SW. The plume dispersed within six hours.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)

Based on analyses of satellite imagery, wind model data, and notices from PVMBG, the Darwin VAAC reported that during 9-15 May ash plumes from Dukono rose to altitudes of 1.5-2 km (4,500-6,000 ft) a.s.l. and drifted E and S.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions at Ebeko on 4 May and during 6-10 May that sent ash plumes as high as 2.4 km (7,875 ft) a.s.l. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

Small ash explosions at Fuego on 11 and 12 May rose to 5 km (15,000 ft) a.s.l., or approximately 1 km (3,280 ft) above the summit. The ash dispersed quickly to the southwest and was visible on webcams.

Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH), Washington Volcanic Ash Advisory Center (VAAC)

Based on satellite data, KVERT reported that during 11-14 May explosions at Karymsky generated ash plumes that rose as high as 3.5 km (11,500 ft) and drifted 145 km SW. 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 at Shinmoedake (Shinmoe peak), a stratovolcano of the Kirishimayama volcano group, an eruption occurred between 1444 and 1610 on 14 May. The plume rose to 4.5 km (15,000 ft) above the crater and drifted SE. A pyroclastic flow travelled 2 km down the flank. Volcanic earthquake rates under the crater increased after the eruption. Shallow, low-frequency earthquakes and tremor were also reported. The Alert Level remained at 3 (on a scale of 1-5).

Source: Japan Meteorological Agency (JMA)

Based on analyses of satellite imagery and model data, the Darwin VAAC reported that on 13 May at 0709 an ash plume from Langila rose to an altitude of 5.5 km (17,000 ft) a.s.l. and drifted W. An image acquired around six hours later indicated that the ash from the event had dissipated.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)

CENAPRED reported that each day during 9-15 May there were 51-137 steam and gas emissions from Popocatépetl as well as ongoing incandescence from the summit. Additionally, three explosions were recorded: at 1834 on 11 May, at 0912 on 11 May, and at 1452 on 14 May. These explosions dispersed ash to the S and SW. Volcano-tectonic earthquakes with magnitudes up to M 2.8 also occurred throughout the time period.

Source: Centro Nacional de Prevencion de Desastres (CENAPRED)

During 9-15 May, IG reported ongoing high levels of eruptive activity at Reventador. Steam, gas, and ash emissions continued, with plumes moving to the N and W. On 12 and 13 May, a small lava flow was observed on the E flank 700 m below the summit.

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

Intermittent ash and gas emissions at Sabancaya during 9-15 May were reported by the Buenos Aires VAAC, with plume altitudes reaching 7-9 km (2,300-3,000 ft) a.s.l.

Source: Buenos Aires Volcanic Ash Advisory Center (VAAC)

KVERT reported that a weak thermal anomaly over Sheveluch was identified in satellite images during 10-14 May. The Aviation Color Code remained at Orange.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

INGV reported typical activity at Stromboli from 7 to 13 May, with 2-4 hourly low-intensity explosions to heights of less than 80 m (300 ft) above the crater, in the North crater area. Fine ash as well as lapilli and bombs were ejected. The South Central crater area vents produced between 5-12 hourly, low-intensity explosions, also to heights of less than 80 m above the crater. Continuous degassing was also observed from these vents. On 13 May there was an increased frequency of explosions, with 16 events/hour. No significant variations were reported in seismological, deformation, or geochemical parameters.

Source: Sezione di Catania - Osservatorio Etneo (INGV)

The Tokyo VAAC reported that explosions occurred at Suwanosejima on 15 May, based on information from JMA.

Source: Japan Meteorological Agency (JMA)

OVSICORI reported that there were strong emissions of SO₂ from Turrialba, accompanied by vigorous fumarolic activity and jetting noises. An ash plume was reported on 10 May, with ashfall in La Pastora de Santa Cruz de Turrialba and Pacayas. A weak water vapor and gas plume was detected at 0920 on 13 May, rising 300-500 m (1000-1600 ft) above the summit. Seismicity was low, with low-amplitude long-period earthquakes and some low-amplitude tremor. Continuous low-amplitude tremor was report on 13 May.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)