Rumblings of a dormant volcano Earthquakes near volcanoes are often a warning sign of a future eruption. However, deep long-period earthquakes (DLPs) are a special type of seismicity tied most often to quiescent volcanoes. Wech et al. found more than a million of these DLPs under the inactive Mauna Kea volcano in Hawai'i over the past 19 years (see the Perspective by Matoza). Analysis of this large number of observations allowed the authors to conclude that the DLPs were connected to a deep, cooling magma body. Deep gas releases triggered by minerals crystallizing in the deep magma through the “second boiling” process may open cracks, triggering the DLPs. Science, this issue p. 775; see also p. 708 More than 1 million deep low-frequency earthquakes are attributed to a cooling, gas-emitting magma body under Mauna Kea, Hawai‘i. Deep long-period earthquakes (DLPs) are an enigmatic type of volcanic seismicity that sometimes precedes eruptions but mostly occurs at quiescent volcanoes. These earthquakes are depleted in high-frequency content and typically occur near the base of the crust. We observed a near-periodic, long-lived sequence of more than one million DLPs in the past 19 years beneath the dormant postshield Mauna Kea volcano in Hawaiʻi. We argue that this DLP sequence was caused by repeated pressurization of volatiles exsolved through crystallization of cooling magma stalled beneath the crust. This “second boiling” of magma is a well-known process but has not previously been linked to DLP activity. Our observations suggest that, rather than portending eruptions, global DLP activity may more commonly be indicative of stagnant, cooling magma.
A. Wech, W. Thelen, A. Thomas