“How Thawing Antarctic Ice Could Ignite Volcanic Fury”

Melting ice sheets are frequently portrayed as representative of climate change in the media, featuring striking images of solitary polar bears adrift on continually diminishing ice rafts. Although consequences such as rising sea levels and changes in salinity are routinely discussed, one less recognized outcome involves the impact on volcanoes.

As the ice sheets, which can be kilometers thick, melt during deglaciation, the mass pressing down on the land diminishes, resulting in uplift. This modifies the pressure within magma chambers located beneath the Earth’s surface, leading to volcanic activity.

A study, published in Geochemistry, Geophysics, Geosystems, implies that the mass unloading caused by the melting of Antarctic ice sheets (isostatic rebound) is instigating eruptions of increased frequency and intensity in the West Antarctic Rift System, which is among the planet’s largest volcanic regions with over 100 eruptive sites.

Ph.D. candidate Allie Coonin from Brown University, along with her team, examined the relationship between glaciation and volcanism over the last two glacial cycles of the planet (within the last 150,000 years).

To achieve this, they employed a thermomechanical magma chamber model and simulated a diminishing West Antarctic Ice Sheet by factoring in specific pressure reductions affecting the underlying rock and magma chamber.

They investigated how this decrease in confining pressure enables the magma chamber to expand in volume, which leads to overpressurization and the release of volatiles (when dissolved gases like water and carbon dioxide form bubbles) from basalt magmas, influencing the patterns of future eruptions.

In their exploration of magma chambers of varying sizes, the research team discovered that larger magma chambers are more vulnerable to the impacts of ice mass unloading, with the unloading rate being the crucial element, the most significant ice loss rate examined reaching 3m/yr.

Moreover, in experiments with magma chambers that were undersaturated in volatiles, the researchers found that ice mass unloading expedited the process of the initial volatile release (kicking off the early stages leading to an eruption) by decades to even centuries.

This indicates that eruptions may have occurred that would not have happened if the unloading had not caused modifications in the magma chamber, leading to a greater cumulative release of magma during that chamber’s lifetime.

To validate their findings, Coonin and her colleagues examined volcanic deposits from the Andes mountains in South America. In this region, the Patagonian ice sheet reached a thickness of 1,600m over the Southern Volcanic Zone between 18,000 and 35,000 years ago. They detected a link between ice mass unloading during the deglaciation phase at the conclusion of the Last Glacial Maximum (~18,000 years ago) and heightened eruptive activity from the Calbuco, Mocho-Choshuenco, and Puyehue-Cordon Caulle volcanoes.

Such volcanism prompted by unloading can result in an unfavorable positive feedback loop, where the melting ice modifies magma chamber pressurization, leading to eruptions that in turn melt more ice, potentially initiating further eruptions. Particularly, as the West Antarctic Ice Sheet is situated below sea level, the rise in sea level linked to melting ice further submerges it, accelerating its retreat.

Adding complexity to the situation are the effects of rising carbon dioxide concentrations that contribute to global warming and ice albedo feedback, where melting ice…sheets decrease the volume of incoming solar radiation returned back to space (there is a reduced ‘white’ reflective surface in contrast to ‘dark’ surfaces that absorb), which elevates the atmosphere’s temperature and intensifies melting.

The investigators observe that even if human-induced warming halted instantly, the consequences of ice mass loss that the West Antarctic Rift System has already undergone will still influence volcanic activities in this region for millennia.

Thus, comprehending the responsiveness of this ice mass loss of the West Antarctic Ice Sheet on magma reservoirs holds significant ramifications for accurately forecasting future impacts on Earth’s interconnected geological frameworks.

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