Stretching, Shaking, Inflating: Volcanic-Tectonic Interactions at a Rifting Silicic Caldera

Abstract

Silicic caldera volcanoes are frequently situated in regions of tectonic extension, such as continental rifts, and are subject to periods of unrest and/or eruption that can be triggered by the interplay between magmatic and tectonic processes. Modern (instrumental) observations of deformation patterns associated with magmatic and tectonic unrest in the lead up to eruptive events at silicic calderas are sparse. Therefore, our understanding of the magmatic-tectonic processes associated with volcanic unrest at silicic calderas is largely dependent on historical and geological observations. Here we utilize existing instrumental, historical and geological data to provide an overview of the magmatic-tectonic deformation patterns operating over annual to 104 year timescales at Taupō volcano, now largely submerged beneath Lake Taupō, in the rifted-arc of the Taupō Volcanic Zone. Short-term deformation patterns observed from seismicity, lake level recordings and historical records are characterized by decadal-scale uplift and subsidence with accompanying seismic swarms, ground shaking and surface ruptures, many of which may reflect magma injections into and around the magma reservoir. The decadal-scale frequency at which intense seismic events occur shows that ground shaking, rather than volcanic eruptions, is the primary short-term local hazard in the Taupō District. Deformation trends near and in the caldera on 101–104 yr timescales are atypical of the longer-term behavior of a continental rift, with magma influx within the crust suppressing axial subsidence of the rift basin within ∼10 km of the caldera margin. Examination of exposed faults and fissures reveals that silicic volcanic eruptions from Taupō volcano are characterized by intense syn-eruptive deformation that can occasionally extend up to 50 km outside the caldera structure, including ground shaking, fissuring and triggered fault movements. We conclude that eruption and unrest scenarios at Taupō volcano depend on the three-way coupling between the mafic-silicic-tectonic systems, with eruption and/or unrest events leading to six possible outcomes initially triggered by mafic injection either into or outside the magma mush system, or by changes to the tectonic stress state.

A study and interpretation of the distribution and kinematics of the 2001 Taupō Fault Belt seismic swarm using relative relocation techniques

“…Outcomes 2 and 5, which envision mafic bodies stalling in the crust having either intruded within or outside the silicic system (Muirhead et al, 2022), are applicable to our results. When a mafic intrusion occurs outside the silicic system but no eruptible silicic melt body in place, the intrusion will result in a change in the stress state around Taupō, unrest and faulting (Muirhead et al, 2022). Examples of this outcome potentially include the faulting and seismicity associated with the 1922 and 1983 swarms within the Taupō Fault Belt (Otway, 1986;Barker et al, 2021;Muirhead et al, 2022).…”

“…This was further expanded on by the work of Muirhead et al (2022), who suggest the presence or absence of eruptible melt bodies is critical in dictating the outcome of mafic recharge or tectonic processes. Both mafic recharge and tectonic processes have the potential to trigger the formation and eruption of a melt body within the shallow silicic system (Leonard et al, 2002;Davis et al, 2007;Baer et al, 2008;Allan et al, 2012).…”

“…Both mafic recharge and tectonic processes have the potential to trigger the formation and eruption of a melt body within the shallow silicic system (Leonard et al, 2002;Davis et al, 2007;Baer et al, 2008;Allan et al, 2012). Muirhead et al (2022) outlined six potential outcomes of volcano-tectonic interactions at Taupō Volcano. Outcomes 2 and 5, which envision mafic bodies stalling in the crust having either intruded within or outside the silicic system (Muirhead et al, 2022), are applicable to our results.…”

“…Muirhead et al (2022) outlined six potential outcomes of volcano-tectonic interactions at Taupō Volcano. Outcomes 2 and 5, which envision mafic bodies stalling in the crust having either intruded within or outside the silicic system (Muirhead et al, 2022), are applicable to our results. When a mafic intrusion occurs outside the silicic system but no eruptible silicic melt body in place, the intrusion will result in a change in the stress state around Taupō, unrest and faulting (Muirhead et al, 2022).…”

“…When a mafic intrusion occurs outside the silicic system but no eruptible silicic melt body in place, the intrusion will result in a change in the stress state around Taupō, unrest and faulting (Muirhead et al, 2022). Examples of this outcome potentially include the faulting and seismicity associated with the 1922 and 1983 swarms within the Taupō Fault Belt (Otway, 1986;Barker et al, 2021;Muirhead et al, 2022). Outcome 2, where a mafic intrusion occurs within the silicic system, was likened to the 2019 seismicity near Horomatangi Reefs beneath Lake Taupō (Illsley-Kemp et al, 2021;Muirhead et al, 2022).…”