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.
Highlights
Silicic caldera volcanoes have demonstrated their capability to produce the largest and most catastrophic explosive volcanic eruptions on Earth
We review the patterns and potential sources of crustalscale deformation at Taupō volcano using a wide range of observational tools to reveal how deformation can manifest on a range of timescales at a rifting silicic caldera, with much of this deformation driven by, or interacting with, the underlying magmatic system
Previously published as incremental updates, here we present the dataset in its entirety with all offsets given relative to site Waihaha (WA) in the Western Bay area of the lake (Figure 5), which occurs to the west of the Taupō Fault Belt and outside the boundaries of modern rifting delineated by Villamor et al (2017)
Summary
Silicic (dacite to rhyolite compositions in this context) caldera volcanoes have demonstrated their capability to produce the largest and most catastrophic explosive volcanic eruptions on Earth. Given the tendency for frequent earthquake activity in regions undergoing extensional strain (e.g., Natron Basin, Tanzania; Lake Malawi Rift, Malawi; Long Valley, U.S.A.: Hill et al, 1995; Biggs et al, 2010; Kolawole et al, 2018; Reiss et al, 2021), it can be challenging to assess whether periods of apparent unrest are associated with magma and/or hydrothermal fluid migration, accommodation of tectonic extension, or a combination of these (Acocella et al, 2015; Illsley-Kemp et al, 2021; Reiss et al, 2021) This is true of silicic caldera systems where the frequency of large earthquakes (M > 5) within close proximity to these volcanoes (i.e.,
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