Although scientists do not fully understand why glaciers appear to weaken volcanic eruptions, they believe the mechanics may be fairly straightforward. When glaciers expand, all that ice puts immense pressure on Earth’s surface. “It can affect magma flow and the voids and gaps in the Earth where magma flows to the surface as well as how much magma the crust can actually hold,” Swindles says. When glaciers retreat, the pressure lifts and volcanic activity surges. “After glaciers are removed the surface pressure decreases, and the magmas more easily propagate to the surface and thus erupt,” Swindles wrote in an e-mail to Scientific American.
This is exactly what he and his team found when they looked at what happened as Earth warmed up again and glaciers melted—they counted more eruptions. Again they saw a time lag, this time between ice melt and the rise in eruptions. But this gap was shorter. “It takes relatively less time to melt ice if the temperature goes up,” compared with growing ice when it gets colder, Swindles says. “So if you’re looking at a period of [warming and subsequent] volcanic flare-up, the lag might be a lot shorter.” He also notes that when volcanic eruptions occur during cooler, ice-covered times, they appear to be smaller in magnitude. As the climate warms, eruptions seem to get bigger.
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