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New supervolcano possibly spotted under the Aleutians

Updated: Jun 1, 2023 02:04 GMT -
Aerial photo showing the Islands of Four Mountains (source: USGS)
Aerial photo showing the Islands of Four Mountains (source: USGS)
A sunken volcano comparable in size to the Yellowstone Caldera in Wyoming, USA, was possibly discovered at the center of the Aleutian Volcanic Arc. This previously unrecognized caldera may be the cause of Cleveland Volcano's activities.
The Early Eocene saw the beginning of what was to be the Aleutian Volcanic Arc west of the Alaskan Peninsula. 56 million years ago, the Pacific Plate collided with- and began its subduction under the North American Plate. As the Pacific Plate was subducted, parts of it melted due to the high pressure and temperature conditions. These molten magmas rose toward the surface. Eventually, volcanoes formed as eruptions of lava occur at the side of the North American Plate. Following millions of years of volcanism in the area, the Aleutian Arc was born.
Location of the Islands of Four Mountains (source: AGU 2020 presentation)
Location of the Islands of Four Mountains (source: AGU 2020 presentation)
Fast forward to 2014, a group of earth scientists led by USGS'John A. Power started a multi-disciplinary study on the lesser studied Central Aleutian Arc. More specifically, they studied the Islands of Four Mountains (IFM) which is actually a group of 6 stratovolcanoes. They are the type of volcano that people usually associate with the word; almost a perfect cone shape, rising high, and usually undergoes explosive eruptions. At the center of it all is the Cleveland Volcano. It is arguably the most active volcano in North America for the past 2 decades. Surrounding Cleveland Volcano are the Herbert, Tana, Uliaga, Carlisle, and Kagamil volcanoes.
Power's team was able to gather evidences that led to their hypothesis of a larger sunken caldera volcano under the IFM, with the above sea-level peaks being the rim. On the virtual American Geophysics Union conference held on December 2020, the team presented on their findings which can be accessed here. Welded ignimbrites were found on Tana and Carlisle. These consolidated pyroclastic materials are consistent with local-caldera forming eruptions.
Looking at the bathymetry of the area, the circular distribution of the 6 volcanoes relative to the whole volcanic arc suggests that a larger structure may be hidden underwater. Geophysical surveys on the area support this as results show a ring-shaped anomaly connecting these volcanoes.

The very active nature of Cleveland Volcano also supports the caldera hypothesis. Oftentimes, volcanoes as active as the Cleveland Volcano are found at the center or at the rim of active calderas. From a geochemical perspective, the high and sustained emission of SO2 from Cleveland, and the composition of volcanic gases from the IFM volcanoes, also suggest a connection to a larger magma source.
The formation of large calderas are also expected in this portion of the Aleutian Arc. High rates of subduction favor caldera formation according to multiple studies conducted on calderas worldwide. There are at least a dozen calderas in the central portions of the Aleutian Arc, with sizes of 5 km to some >10 km.
However, Power reiterated in their AGU presentation that their findings does not confirm the presence or size of any caldera beneath IFM. More studies should be made and samples should be gathered in order to confirm their hypothesis. Nevertheless, they stated both on paper and on presentation that there are no immediate threats of a caldera eruption in the area.

Studying caldera forming eruptions are important because they can be large enough to impact the world's climate. This alone could affect agricultures, start pandemics, and even cause political instabilities. Another great and interesting read is on the Okmok Caldera still in the Aleutian Arc. A study by McConnell et al. (2020), explores on the effects of the massive eruption of Okmok in 43 BCE which caused extreme climate changes. These might have contributed to (if not caused) the downfall of the Roman Republic and Ptolemaic Kingdom, leading to the rise of the Roman Empire.
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