Bogoslof volcano is the ephemeral top of a submarine volcano in the central Aleutians. It is located some 40 km north of Okmok and Umnak Island, and some 100 km west of Unalaska on Unalaska Island which is also the closest village with 4,200 people. The island is small enough and low enough that any volcanic activity at all significantly rearranges the visible portion of the island above the waves. Additionally, the action of the Bering Sea also does a number on the soft material making up most of the island.
Unalaska’s primary industry is commercial fishing, seafood processing, fleet services and marine transportation. It is the last large port, processing and support facility as you travel westward along the Aleutians.
The submarine volcano is some 1,800 m tall and extends above sea level some 150 m. The island itself before the most recent eruption was triangular in shape, less than 2 km long, and less than 0.75 km wide at its widest point.
Bogoslof Island consists of the remains of several domes and spires from eruptions since its discovery in 1796. The eruptions that manufactured the domes and spires were not sufficient to build a larger island and the action of water and waves over time quickly erodes the part of the island above the waves. Explosive eruptions also do their part to significantly change the shape and nature of the island. From time to time, there is more than a single island at the location.
The island is uninhabited and was been designated part of the Aleutians Wilderness in 1970.
The island is a haulout / breeding ground for seals, sea lions and hosts a large number of birds with as many as 90,000 puffins, guillemots, kittiwakes and gulls nesting from time to time.
The fur seal population established itself with the first pup born in the 1980s. It has increased significantly over the last three decades and provided an example of the growth of a new population of seals. Fortunately, winter in the Aleutians is not the breeding season, so the destruction and rebuilding of the island due to the eruptions will not kill any residents, though it will destroy borrows dug by some species of nesting puffins. And no, I don’t know where they go during the winter. https://www.adn.com/wildlife/article/bogoslof-island-newly-formed-fur-seal-population-draws-researchers/2015/09/27/
Weather is generally wet and moderately cold with average highs in August just above 12C and lows in February -1.4C. In neighboring Unalaska, 923 mm of precipitation falls annually. The region is generally ice free during the winter.
The AVO Bogoslof page can be found here: https://www.avo.alaska.edu/activity/Bogoslof.php
The island itself does not have any webicorders installed, though the AVO web site lists one as the Bogoslof webicorder. Looks like they are taking the feed off a pair of Okmok webicorders and one near Unalaska to provide its data. https://www.avo.alaska.edu/webicorders/Bogoslof/OKER.php
Bogoslof exploded into action via pilot report (pirep) on Dec 20 of an airborne plume over the island from what ended up being a short eruption. The plume topped out at some 10 km. Note that there are no instruments on the island, so plume heights are measured either by pireps or satellite temperature measurements of the top of the plume. Remote webicorders around Okmok and Unalaska recorded the initial eruption. Ash was drifting south. A second pirep an hour later reported that the original eruption had ended. https://www.adn.com/alaska-news/2016/12/20/pilots-report-eruption-of-bogoslof-volcano-warnings-issued/
Two days and two eruptions later, the volcano was showing nearly continuous activity with the eruptive plume visible from Unalaska some 100 km east. By this time, the prevailing winds were blowing north and the ash and SO2 from the eruption were also moving north with it. This plume also topped out around 10km. A pair of pireps reported strong sulphur smell but no ash between 10 – 11 km high east of Bethel. The vent was located on the pre-eruption eastern edge of the island, about 80% of the way north along that edge. The first couple eruptions also removed most of that side of the island, leaving the vent now underwater. AVO published the first drawing and annotated satellite photo of the newly rearranged island. This was not the last time the island was rearranged during the eruption sequence. https://www.adn.com/alaska-news/science/2016/12/22/aleutians-bogoslof-volcano-still-rumbling-after-2-eruptions-in-2-days/
The fourth eruption took place the next day on Friday, Dec. 23 and lasted just over an hour. Plume topped out around 9 km. There was a Coast Guard vessel in the vicinity which took a photo of what appeared to be Strombolian activity with chunks of debris being tossed into the air and lightning in the plume. By this time the weather was changing with three Bering Sea storm systems merging and moving east up the Aleutian chain. https://www.adn.com/alaska-news/science/2016/12/23/bogoslof-volcano-erupts-again-sends-up-30000-foot-ash-plume/
While restless, eruptions calmed down until Friday, Dec. 30, when another eruption took place overnight putting a plume some 6 km into the air. There was another eruption the following day in Dec. 31. While the article describing the eruption late last week specifically did not mention ashfall at Unalaska, at least one commenter to the article reported it. https://www.adn.com/alaska-news/science/2016/12/30/alert-again-raised-for-aleutians-volcano-after-new-eruption/
There was a minor explosion on Jan. 1 around 2 PM local observed via seismograph. No ash or plume was observed above the clouds, leading AVO to believe it was a relatively small eruption. https://www.adn.com/alaska-news/2017/01/02/bogoslof-volcano-continues-grumbling-in-aleutians/
Another short-lived eruption took place in the evening of Jan 3. It was recorded via seismic, satellite and lightning detectors. Prevailing winds at the time were to the north. The local paper description puts the plume top above 11 km, though I doubt that conclusion. AVO still carries the volcano as a Red / Warning status. https://www.adn.com/alaska-news/2017/01/02/bogoslof-volcano-continues-grumbling-in-aleutians/
As of this writing, it appeared for a while that the explosive portion of the eruption was winding down a bit. As this week went on, AVO was yo-yoed to the point where they were having a hard time deciding what status the volcano really was (orange vs red). We know the volcano has a history of eruptions followed by dome building. How long this process takes this time around remains to be seen.
Bogoslof was first sighted in 1768 by Captain Cook. There was a rocky outcrop (dome spine) called Sail Rock. It disappeared between 1884 – 1891. The larger island was formed during an eruption in 1796 and named Ioann Bogoslof (John the Apostle) by Russian mariners.
By the time a new dome north of Bogoslof was discovered around 1883 (a good year for volcanoes), ownership of Alaska had been transferred to the United States and Americans were starting their first scientific investigations into Umiak and Bogoslof islands. This dome was called Fire Island.
Volcanic activity began again between 1906 – 1907. There was a 1910 eruption that extruded another dome named Tahoma Peak. Another eruption took place between 1926 – 1927.
Bogoslof is largely submerged and considered a back-arc volcano. It rises some 1,500 m from the ocean floor (reported as 1,800 m in places). At the point where Bogoslof and Okmok are located, the Aleutians are a single-island volcanic arc. It is primarily an andesitic / basaltic andesite volcano. Some basalt and trachyandesite has also been observed from it.
10 – 11 historic eruptions have been observed from Bogoslof. The first one was 1796 and the last one was 1992. Stop dates for three on the list are unknown. Eruption VEI for those three are also uncertain. Typical strength of the remaining known eruptions is in the VEI 2 -3 range.
Volcanic activity in the central Aleutians are subduction driven by the Pacific Plate diving under the North American Plate. Volcanic products are largely andesitic and basalt with some variations based on the length of time between eruptions. Bogoslof is located on a spur north of the main arc.
Bogoslof has been active since its discovery. Most eruptive sequences appear to end with some sort of dome building. There seems to be insufficient supply of magma to build a large, long-lived island above the wave tops, so the volcano pokes its head above the waves from time to time and the action of wind, water and subsequent eruptions significantly change the size, shape and duration of the island over time. Activity has been observed since the island was discovered. There is no reason to believe this will change in an meaningful way in the not so distant future.