Bogoslof Island

Bogoslof Island
	Aerial view of Bogoslof Island looking south (1994)
Waters	Bering Sea
Archipelago	Aleutian Islands ( Alaska )
Geographical location	53 ° 56 ′ 9 ″ N , 168 ° 2 ′ 20 ″ W Coordinates: 53 ° 56 ′ 9 ″ N , 168 ° 2 ′ 20 ″ W
length	1.4 km
width	600 m
surface	28.8 ha
Highest elevation	Castle Rock ; 150 m
Residents	uninhabited
	Bogoslof Island on April 20, 2018, illustration of the significant changes in terrain caused by eruptions

Bogoslof Island is a small uninhabited volcanic island of the Fox Islands , part of the Aleutian Islands . The island, which was around 1.4 km long and 0.288 km² in size until 2016, is located north of Umnak .

Mostly submarine volcano

Bogoslof Island is the top of a submarine volcano rising 1,500 meters above the bottom of the Bering Sea . The volcano has erupted several times in historical times, the eruptions have repeatedly made the island disappear and reappear in other places, which has led to a confusing name. The current island is the remnant of various lava domes from the 1796-1992 eruptions. Fire Island , about 600 meters northwest, is a remnant of the 1883 eruption.

The Alaska Volcano Observatory has no sensors on the island and is therefore dependent on optical and seismic observations from a distance.

Outbreak 2016/2017

On December 12, 2016, the volcano's most recent eruptive phase began with smaller ash eruptions. On December 16 and 19, lightning bolts were located in the area around the island, indicating discharges in a water-laden ash cloud. On December 20, 2016, shortly before 4 p.m. local time, there was a powerful phreatomagmatic explosion of the volcano, in which an ejected ash cloud rose to a height of 10.3 kilometers. Other similarly strong explosive ash eruptions occurred through August 30, 2017. The highest ash rise up to a height of 10.7 kilometers was measured several times, namely on December 21 and 26, 2016 and on January 5 and 8, 2017.

The outbreak on December 21, 2016 released a large amount of sulfur dioxide, which could still be detected five days later over Nebraska (in the middle of the trunk states of the USA). In an explosion on January 18, 2017, fresh lava was first detected on the ground near the chimney.

The newly created chimney was under water in the northeast of the island near the former coastline, a little south of the chimney of the last eruption in 1992 until the end of January 2017. The northeast of the island was destroyed in the strong eruption on December 20, 2016, so that according to satellite observations on December 25th three separate, closely spaced islands existed, which were connected by a shallow water zone. A small island to the northeast was newly created. The northern tip of the original island had been severed. The rest of the main island has been significantly deformed by erosion (including the southeastern tip) and deposits. The westernmost point in the north-west of the island was retained as the westernmost point at the time. The northernmost point also remained, but was separated with a small area. The south-eastern tip of the island had withdrawn a little to the north.

Due to further eruptions, the three individual islands were reunited to form an island by January 10, 2017, which, however, has a completely different shape than the original island. The character of the island as the tip of a volcano now became very clear, as the north-east at that time consisted of an almost circular bay, which was surrounded on three sides by land mass and has been slowly filling with volcanic material since January 10th. A satellite image from January 31, 2017 shows that the bay was now filled with ash and the chimney was separated from the sea. Much of the island has since consisted of fresh deposits of volcanic ash, which can be eroded again by ocean waves. The area of the island has more than tripled by the end of January 2017 from the original (2015) 0.288 km² to 1.02 km². During the subsequent eruptions, little has changed in the basic shape of the island. The trough, now recognizable as the main crater, had been filled with water since January, which led to some phreatic eruptions. For several months, water vapor was observed standing over the crater lake. At the beginning of December 2017, the eruptive phase was declared over and the alert level lifted. It ended with the last known outbreak on August 30, 2017.

Air traffic between North America and Asia had to avoid the ash clouds several times and flight operations to Unalaska Airport had to be suspended at times .