Goldilocks conditions required for earthquakes to trigger basaltic eruptions: Evidence from the 2015 Ambrym eruption

Abstract

Observations indicate a strong correlation between the occurrence of volcanic eruptions and earthquakes. While increased volcanic activity has been observed following both local and distal earthquakes, some of the largest recorded earthquakes aren’t known to have triggered an eruption. Here we investigate whether an eruption and associated dike intrusion at Ambrym volcano was triggered by an Mw 6.4 earthquake which occurred 30 hours earlier. Modeling suggests that stress changes induced by the earthquake were too small to account for the overpressure in the dike without additional bubble growth to pressurize the magma chamber. We find that the magma must be both H2O-saturated and at lower temperatures than those expected for newly intruded basalts. Too hot and the stress drop required to grow the bubbles is too large, too cold and the magma can no longer flow. These observations suggest that partially cooled and crystallized basaltic magmas are more susceptible to triggering from earthquakes.

A review framework of how earthquakes trigger volcanic eruptions

“…These mechanisms may then be tested for validity. For instance, static stress changes can be computed numerically 35,69,72,73 , occurrence of resonant oscillations can be measured, crystal and bubble textures may retain a signature of nucleation events, and hydrothermal processes can be constrained with seismic monitoring 205 and electromagnetic surveys 206 . Constraining the triggering mechanisms for a given type of volcano will be useful for future statistical studies, but may also inform and guide monitoring strategies and hazard assessment.…”

“…One of the reasons why earthquakes do not trigger more volcanic eruptions, and why some very large earthquakes trigger very little activity (e.g. Sumatra M9.2 2004 earthquake 6 ), is that the range of conditions where seismic triggering is possible forms a very narrow window that is not often met 7,35 . In particular, many studies have highlighted the need for a volcano to already be in a critical state in order to be seismically triggered 4,6,7,10,13,19,25,27,32,33,48,56,57,137,207 .…”

“…The phenomenon is well known in other fluids, in particular in water 93 , and usually referred to as cavitation. Static decompression may sometimes be sufficient to trigger nucleation 23,33,35 . Pressure oscillations in the fluid can locally change the solubility and diffusivity of volatiles (mostly water), thus accelerating bubble formation processes.…”

“…There are documented cases of both changes from quiescence to eruption 6,20,29,[32][33][34][35] , and changes in style of an ongoing eruption [36][37][38][39][40] in the weeks following an earthquake. Earthquakes may also trigger a broad spectrum of non-eruptive unrest phenomena including increased seismicity 25,[41][42][43][44][45] , degassing 17,25,34,46,47 , heat flux [26][27][28]48 or subsidence 49,50 .…”

Persistent Long‐Period Signals Recorded by an OBS Array in the Western‐Central Pacific: Activity of Ambrym Volcano in Vanuatu

“…It is characterized by a 12‐km‐wide caldera hosting two active cones, Marum and Benbow. The volcano recently erupted in February 2015 and in December 2018 (Hamling et al, 2019; Hamling & Kilgour, 2020). The intensification of the 25 and 18 s signals is observed in the spectral densities (Figure 3d), and the one on 20 February 2015 corresponds to the intra‐caldera minor eruption (Figure S5 and Hamling & Kilgour, 2020).…”