Before and AfterIn the latter part of December, a small volcanic island off th…

Before and After

In the latter part of December, a small volcanic island off the coast of Alaska suddenly awakened. That island represents a volcano called Bogoslof – a volcano in the Aleutian Island chain that rises slightly above the waters of the Pacific. Prior to December, its last known eruption was in 1992, so the picture at the left represents basically how this small hunk of rock looked in early December.

The Alaska Volcano Observatory released the second photo this week. Although several features (marked by numbers) are clearly visible, after the series of ongoing explosive eruptions several major changes have happened in the shape of the island, with the expansion most likely representing growth of the volcano through new lava flows or deposition of tephra.

The actual center of the eruption is a crater at the center of the semicircular island. The activity is ongoing, and at the time of this photo the darker water likely represents a mixture of ocean water and volcanic tephra produced by the most recent volcanic output.

The Aleutian Islands lie above a subduction zone where the Pacific Plate sinks into the mantle. In the process the downgoing plate gives off water that reduces the melting point of mantle rocks, eventually producing a chain of volcanoes above it called a volcanic arc. The entire Alaskan Peninsula, the Aleutian Islands, and the Kamchatka Peninsula are all made of volcanic rocks produced by this process.


Image credits: AVO

More on the eruptions: