The Role of Magma Overpressure in Suppressing Earthquakes and Topography: Worldwide Examples

Triggering of eruptions at Axial Seamount, Juan de Fuca Ridge

The submarine volcano Axial Seamount has exhibited an inflation predictable eruption cycle, which allowed for the successful forecast of its 2015 eruption. However, the exact triggering mechanism of its eruptions remains ambiguous. The inflation predictable eruption pattern suggests a magma reservoir pressure threshold at which eruptions occur, and as such, an overpressure eruption triggering mechanism. However, recent models of volcano unrest suggest that eruptions are triggered when conditions of critical stress are achieved in the host rock surrounding a magma reservoir. We test hypotheses of eruption triggering using 3-dimensional finite element models which track stress evolution and mechanical failure in the host rock surrounding the Axial magma reservoir. In addition, we provide an assessment of model sensitivity to various temperature and non-temperature-dependent rheologies and external tectonic stresses. In this way, we assess the contribution of these conditions to volcanic deformation, crustal stress evolution, and eruption forecasts. We conclude that model rheology significantly impacts the predicted timing of through-going failure and eruption. Models consistently predict eruption at a reservoir pressure threshold of 12–14 MPa regardless of assumed model rheology, lending support to the interpretation that eruptions at Axial Seamount are triggered by reservoir overpressurization.

Initial pulse of Siberian Traps sills as the trigger of the end-Permian mass extinction

Mass extinction events are short-lived and characterized by catastrophic biosphere collapse and subsequent reorganization. Their abrupt nature necessitates a similarly short-lived trigger, and large igneous province magmatism is often implicated. However, large igneous provinces are long-lived compared to mass extinctions. Therefore, if large igneous provinces are an effective trigger, a subinterval of magmatism must be responsible for driving deleterious environmental effects. The onset of Earth’s most severe extinction, the end-Permian, coincided with an abrupt change in the emplacement style of the contemporaneous Siberian Traps large igneous province, from dominantly flood lavas to sill intrusions. Here we identify the initial emplacement pulse of laterally extensive sills as the critical deadly interval. Heat from these sills exposed untapped volatile-fertile sediments to contact metamorphism, likely liberating the massive greenhouse gas volumes needed to drive extinction. These observations suggest that large igneous provinces characterized by sill complexes are more likely to trigger catastrophic global environmental change than their flood basalt- and/or dike-dominated counterparts.

Although the mass end-Permian extinction is linked to large igneous provinces, its trigger remains unclear. Here, the authors propose that the abrupt change from flood lavas to sills resulted in the heating of sediments and led to the release of large-scale greenhouse gases to drive the end-Permian extinction.

Late Quaternary faulting in the Sevier Desert driven by magmatism

Seismic hazard in continental rifts varies as a function of strain accommodation by tectonic or magmatic processes. The nature of faulting in the Sevier Desert, located in eastern Basin and Range of central Utah, and how this faulting relates to the Sevier Desert Detachment low-angle normal fault, have been debated for nearly four decades. Here, we show that the geodetic signal of extension across the eastern Sevier Desert is best explained by magma-assisted rifting associated with Plio-Pleistocene volcanism. GPS velocities from 14 continuous sites across the region are best-fit by interseismic strain accumulation on the southern Wasatch Fault at c. 3.4 mm yr⁻¹ with a c. 0.5 mm yr⁻¹ tensile dislocation opening in the eastern Sevier Desert. The characteristics of surface deformation from field surveys are consistent with dike-induced faulting and not with faults soling into an active detachment. Geologic extension rates of c. 0.6 mm yr⁻¹ over the last c. 50 kyr in the eastern Sevier Desert are consistent with the rates estimated from the geodetic model. Together, these findings suggest that Plio-Pleistocene extension is not likely to have been accommodated by low-angle normal faulting on the Sevier Desert Detachment and is instead accomplished by strain localization in a zone of narrow, magma-assisted rifting.

Seismic Anisotropy Beneath Ruapehu Volcano: A Possible Eruption Forecasting Tool

The orientation of crustal seismic anisotropy changed at least twice by up to 80 degrees because of volcanic eruptions at Ruapehu Volcano, New Zealand. These changes provide the basis for a new monitoring technique and possibly for future midterm eruption forecasting at volcanoes. The fast anisotropic direction was measured during three seismometer deployments in 1994, 1998, and 2002, providing an in situ measurement of the stress in the crust under the volcano. The stress direction changed because of an eruption in 1995-1996. Our 2002 measurements revealed a partial return to the pre-eruption stress state. These changes were probably caused by repeated filling and depressurizing of a magmatic dike system.

Changes in seismic anisotropy after volcanic eruptions: evidence from Mount Ruapehu

The eruptions of andesite volcanoes are explosively catastrophic and notoriously difficult to predict. Yet changes in shear waveforms observed after an eruption of Mount Ruapehu, New Zealand, suggest that forces generated by such volcanoes are powerful and dynamic enough to locally overprint the regional stress regime, which suggests a new method of monitoring volcanoes for future eruptions. These results show a change in shear-wave polarization with time and are interpreted as being due to a localized stress regime caused by the volcano, with a release in pressure after the eruption.

Anomalous strain accumulation in the yucca mountain area, nevada

Global Positioning System (GPS) surveys from 1991 to 1997 near Yucca Mountain, Nevada, indicate west-northwest crustal elongation at a rate of 1.7 +/- 0.3 millimeters per year (1final sigma) over 34 kilometers, or 50 +/- 9 nanostrain per year. Global Positioning System and trilateration surveys from 1983 to 1997 on a 14-kilometer baseline across the proposed repository site for high-level radioactive waste indicate that the crust extended by 0.7 to 0.9 +/- 0.2 millimeter per year (50 to 64 +/- 14 nanostrain per year), depending on the coseismic effect of the Ms 5.4 1992 Little Skull Mountain earthquake. These strain rates are at least an order of magnitude higher than would be predicted from the Quaternary volcanic and tectonic history of the area.