ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, July 15, 2022, 12:18 PM AKDT (Friday, July 15, 2022, 20:18 UTC)
Slow eruption of lava from the summit crater of Great Sitkin Volcano continued this week. Weakly elevated surface temperatures were observed at the summit in satellite data most days when the volcano was not obscured by clouds. Seismic activity remains low with occasional small local earthquakes detected throughout the week. Satellite-based radar observations showed thickening of the lava flow around the vent but no significant changes in the lengths of the lava flows.
The terrain is steep near the terminus of the lava flow lobes, and blocks of lava could detach without warning and form small rock avalanches in these valleys. These avalanches may liberate ash and gas and could travel several hundred meters beyond the lava flows; they would be hazardous to anyone in those areas.
Great Sitkin is monitored by local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.
Great Sitkin Volcano is a basaltic andesite volcano that occupies most of the northern half of Great Sitkin Island, a member of the Andreanof Islands group in the central Aleutian Islands. It is located 26 mi (43 km) east of the community of Adak. The volcano is a composite structure consisting of an older dissected volcano and a younger parasitic cone with a 1.5 km-diameter summit crater. A steep-sided lava dome, emplaced during the most recent significant eruption in 1974, occupies the center of the crater. That eruption produced at least one ash cloud that likely exceeded an altitude of 25,000 ft (7.6 km) above sea level. A poorly documented eruption occurred in 1945, also producing a lava dome that was partially destroyed in the 1974 eruption. Within the past 280 years a large explosive eruption produced pyroclastic flows that partially filled the Glacier Creek valley on the southwest flank.
Pavlof Volcano continues to erupt from the active vent on the east flank just below the volcano’s summit. Seismic tremor and elevated surface temperatures in satellite data were observed throughout the week, which may reflect ongoing minor lava effusion. Beginning July 10, numerous explosions were detected daily in seismic and infrasound data with associated minor ash emissions observed in occasionally clear web camera images. No significant ash emissions were observed in satellite data.
Periods of lava spatter and fountaining from the vent on the volcano’s upper east flank have been occurring since mid-November 2021. This activity has built a small cone and sent flows down the flank that melt the snow and ice and produce variable amounts of meltwater. The meltwater typically incorporates loose debris on the flank of the volcano and forms thin (less than 2 m thick) lahars. The lahar deposits extend down the east-southeast flank for several kilometers, not quite to the base of the volcano.
Previous eruptions of Pavlof indicate that the level of unrest can change quickly and the progression to more significant eruptive activity can occur with little or no warning.
Pavlof is monitored by local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.
Pavlof Volcano is a snow- and ice-covered stratovolcano located on the southwestern end of the Alaska Peninsula about 592 mi (953 km) southwest of Anchorage. The volcano is about 4.4 mi (7 km) in diameter and currently has active vents on the north and east sides close to the summit. With over 40 historic eruptions, it is one of the most consistently active volcanoes in the Aleutian arc. Eruptive activity is generally characterized by sporadic Strombolian lava fountaining continuing for a several-month period. Ash plumes as high as 49,000 ft (15 km) above sea level have been generated by past eruptions of Pavlof, and during the March 2016 eruption, ash plumes as high as 40,000 ft (12.2 km) above sea level were generated and the ash was tracked in satellite data as distant as eastern Canada. The nearest community, King Cove, is located 30 mi (48 km) to the southwest of Pavlof.
Unrest continues at Cleveland volcano. Elevated surface temperatures from hot degassing in the summit crater were observed in satellite data most days this past week. Sulfur dioxide emissions were observed in satellite data on July 13 and 14. Analysis of satellite data this week shows continued minor subsidence of the southern crater wall, possibly reflecting subsurface changes within the upper part of the volcano. Seismic activity remains low and there have been no observations of explosive activity detected in seismic and infrasound data over the past week.
Episodes of lava eruption and explosions can occur at Cleveland without advance warning. Explosions are normally short duration and only present a hazard to aviation in the immediate vicinity of the volcano. Larger explosions that present a more widespread hazard to aviation are possible but are less likely and occur less frequently.
Cleveland volcano is monitored by only two seismic stations, which restricts AVO's ability to precisely locate earthquakes and detect precursory unrest that may lead to an explosive eruption. Rapid detection of an ash-producing eruption may be possible using a combination of seismic, infrasound, lightning, and satellite data.
Cleveland volcano forms the western portion of Chuginadak Island, a remote and uninhabited island in the east central Aleutians. The volcano is located about 45 miles (75 km) west of the community of Nikolski, and 940 miles (1500 km) southwest of Anchorage. The most recent significant period of eruption began in February 2001 and produced 3 explosive events that generated ash clouds as high as 39,000 ft (11.8 km) above sea level. The 2001 eruption also produced a lava flow and hot avalanche that reached the sea. Since then, Cleveland has been intermittently active producing small lava flows, often followed by explosions that generate small ash clouds generally below 20,000 ft (6 km) above sea level. These explosions also launch debris onto the slopes of the cone producing hot pyroclastic avalanches and lahars that sometimes reach the coastline.
Low-level unrest continues at Semisopochnoi volcano. Seismicity remained elevated with intermittent earthquakes and periods of seismic tremor throughout the week. Sulfur dioxide emissions from the volcano were observed in satellite data on July 12, 13 and 14. Clear web camera views early in the week showed consistent steam emissions from the north crater of Mount Cerberus before cloudy conditions obscured views of the volcano later in the week. No explosive activity was observed in seismic or infrasound data.
Small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Cerberus and ash clouds usually under 10,000 ft (3 km) above sea level have characterized the recent activity and could begin again with little warning.
Semisopochnoi is monitored by local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.
Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The volcano is dominated by a 5-mile (8 km) diameter caldera that contains a small lake and several post-caldera cones and craters. The age of the caldera is not known with certainty but is likely early Holocene. Prior to 2018, the previous known historical eruption of Semisopochnoi occurred in 1987, probably from Sugarloaf Peak on the south coast of the island, but details are lacking. Another prominent, young post-caldera landform is Mount Cerberus, a three-peaked cone cluster in the southwest part of the caldera. The island is uninhabited and part of the Alaska Maritime National Wildlife Refuge. It is located 40 mi (65 km) northeast of Amchitka Island and 130 mi (200 km) west of Adak.
OTHER ALASKA VOLCANOES
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