Scientists find giant magma reservoirs under dormant volcanoes in the Cascades

Scientists have found giant magma reservoirs under dormant volcanoes in the Cascades. A new study shows that the magma system can persist even after eruptions.

Volcanoes in the Cascades region of the Northwest Pacific Ocean are still supported by large reservoirs of magma. These magma reservoirs have existed for thousands of years without causing eruptions, Live Science writes.

For a long time, scientists have been searching for an answer to whether magma can be stored in the upper crust beneath volcanoes for a long time, or whether it moves to these shallow regions shortly before eruption. The new study shows that, at least in the Cascades, these magma reservoirs exist regardless of the frequency of eruptions.

"It appears that these magma bodies exist beneath volcanoes throughout their lifetime, not just during their active state," said first author Guanning Pang, a doctoral candidate in earth sciences at Cornell University in the United States.

The new discoveries were made thanks to the modernization of the USGS seismic monitoring stations in the Cascade Mountains, which allowed Pang and his co-authors to track the waves of distant earthquakes as they passed beneath Mount St. Helens, Mount Rainier, Lassen Peak, and other nearby volcanoes.

During the study, they noticed a consistent slowing of the earthquake wave speed – sometimes by 70% – under the volcanic peaks. According to the scientists, these slowdowns are too large to be explained by factors such as temperature. Waves travel more slowly through liquids than through solids, so the results show that large reservoirs of magma are hiding about 5 to 15 kilometers below the surface.

Magma reservoirs are not like underground lakes of fire. Rather, they are made of porous rock through which liquid magma moves. Only when the proportion of liquid magma exceeds 35% does the reservoir have the potential to erupt. Scientists do not have direct measurements of what percentage of the magma beneath these mountains has melted, but they estimate that it could range from 3% to 32%.

However, even if the melt level reaches 32%, it does not necessarily portend an eruption, as this percentage can hold for decades or decrease depending on local conditions. In any case, scientists see no evidence that these reservoirs are ready for an eruption.

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