Fast melt expulsion from crystal-rich mushes via induced anisotropic permeability

Abstract

Catastrophic eruptions of rhyolitic super volcanoes require large volumes of silicic magma to be extracted from a crystal-rich mush at high rates. However, fast melt extraction is thought to be difficult because of the low permeability of mushes and the high viscosities of silicic melts. Here, we show that induced ephemeral high permeability pathways in the mush may be critical. During uniaxial compression of the mush, driven by the impingement of recharging magmas from below, melt within the mush can be redistributed preferentially into vertical melt pockets. This redistribution of melt can increase vertical permeability by a factor of 10-100 times, which leads to rapid expulsion of melt. As melt is expelled, the permeability rapidly declines. The end result is a fast, short-lived pulse of melt extraction that can grow a 1 km thick silicic magma reservoir in 10 kyr. Our analysis shows how the incursion of deep-seated magmas into the base of a crystal-rich mush in the crust can trigger the expulsion of silicic melts that may lead to an eruption.