Source: US Geological Survey
Far out in Alaska’s Bering Sea, Bogoslof Volcano rises from the ocean floor—an underwater giant with just a sliver of land showing above the waves. Although it looks small from the surface, the volcano is massive beneath the sea, and it plays an important role in helping scientists understand how underwater volcanoes grow, erupt, and sometimes collapse. We’re currently aboard the research vessel Atlantis, using the deep-sea submersible, the human-occupied vehicle Alvin to explore and collect samples from the seafloor around Bogoslof.
Bogoslof’s most recent eruption, from December 2016 to August 2017, was one of the most dramatic volcanic events in recent Alaskan history. Over nine months, it produced at least 70 explosions. Many of these happened underwater, where magma and seawater reacted violently. The blasts sent ash clouds as high as 10 kilometers into the sky, disrupted air travel across the North Pacific, and repeatedly reshaped the island’s surfaces.
On this expedition, we have used Alvin to collect rock samples from two different spots on the underwater flanks of the volcano. The first location appears to be part of an old lava flow, based on its shape and the thick layer of marine life growing on it. The second site is more mysterious—it might be a small volcanic cone, a block from an underwater landslide, or something else entirely. We don’t yet know how old these rocks are or exactly how they formed, but they will help us piece together Bogoslof’s long and complex history.
We also saw that both dive sites were covered in fine sediment, likely made up of volcanic ash and debris from past eruptions. These layers give clues about how material spreads across the seafloor and may also affect the stability of the volcano’s slopes.
Bogoslof is unusual even among Alaskan volcanoes. It sits north of the main Aleutian volcanic arc and has a different chemical makeup than most of its neighbors. Nearly the entire volcano is underwater, which makes it hard to study and even harder to predict. Before this expedition, very few rock samples had ever been collected from its flanks.
Our work is helping to change that. By collecting samples directly from the underwater parts of the volcano, we’re learning how Bogoslof formed, how it changes during eruptions, and what kinds of hazards it might pose in the future. Each dive adds new pieces to the puzzle of this fascinating volcano hidden beneath the waves.