Ongoing eruptions at Bogoslof Volcano Eruption of December 2016 – January 2017

Initial plume from Bogoslof on Dec. 20, 2016. Photo courtesy AVO via NYT. http://www.nytimes.com/2016/12/30/science/an-alaskan-volcano-bogoslof-erupts-largely-out-of-view.html?ref=oembed&_r=0

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.

Dutch Harbor, Unalaska, Alaska. Primary commercial fishing target is pollock, sablefish, salmon and king crab. http://www.whatsinport.com/Dutch-Harbor-Unalaska-Island.htm

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.

Castle Rock dome remnant on Bogoslof. Note the bird activity. Photo courtesy AVO. https://www.avo.alaska.edu/images/image.php?id=41242

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.

Bogoslof sea lion rookery summer 2015. Photo courtesy ADN. https://www.adn.com/wildlife/article/bogoslof-island-newly-formed-fur-seal-population-draws-researchers/2015/09/27/

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/

Oblique view of Okmok and Bogoslof looking east along the Aleutian chain. Photo courtesy AVO 2011. https://www.avo.alaska.edu/images/image.php?id=103431

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 plume from Unalaska Dec 21, 2016. Photo courtesy AVO / ADN reader submission https://www.avo.alaska.edu/images/image.php?id=103561

Current Activity

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/

A pair of Bogoslof eruptions on Dec 28. Webicorder located on Unmak island monitoring Okmok caldera. Photo courtesy AVO https://www.avo.alaska.edu/images/image.php?id=103651

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/

Bogoslof webicorder from Okmok Dec 30, 2016. Eruption is the first extended line from 0520 – 0620 Dec 29. Image courtesy AVO.

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/

Ash trajectory forecast for 30 Dec. 2016 from Bogoslof. DLG is Dilingham, AK. Photo courtesy Air Resources Laboratory / Forecast Trajectory Maps for Alaskan Volcanoes, Jan 1, 2017. http://ready.arl.noaa.gov/READY_traj_alaska.php

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 dome building August 11, 1891 https://www.wdl.org/en/item/16014/

Volcano

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.

Bogoslof submarine eruption between 1896 – 1913. Photo Courtesy KTUU and AVO. http://www.kt va.com/pilots-report-eruption-bogoslof-island-volcano-avo-issues-warning-769/

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.

1906 photo of still smoking Perry Island (Metcalf Domes) on Bogoslof. Photo courtesy AVO. https://www.avo.alaska.edu/images/image.php?id=14258

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.

Bogoslof taken from the north. Note the 3 dome remnants. The light-colored dome on the left was created in the 1992 eruption. The flat round dome in the center foreground was produced in the 1927 eruption. The Pinnacle in the right background is Castle Rock, produced during the 1796 eruption. Photo taken June 1998, courtesy AVO. https://www.avo.alaska.edu/images/image.php?id=14112

 

Aleutian Subduction Zone and Aleutian Trench. Okmok and Bogoslof are at the far right of the string of islands. http://geosphere.gsapubs.org/content/8/6/1254/F12.expansion.html

Tectonics

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.

Satellite image of 26 Dec plume some 22 hours after the eruption began. Plume is some 7 km high. Photo courtesy AVO. https://www.avo.alaska.edu/images/image.php?id=103601

Conclusions

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.

Shoreline change in Bogoslof due to eruptive events on Dec 22 and Dec 25. Photo courtesy AVO and USGS. https://www.avo.alaska.edu/images/image.php?id=103621

Additional information

https://volcano.si.edu/volcano.cfm?vn=311300
https://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=bogoslof
https://www.adn.com/alaska-news/science/2016/12/30/alert-again-raised-for-aleutians-volcano-after-new-eruption/

 

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