Low-temperature thermal unrest and deformation at active volcanoes: The intriguing case of Domuyo and Taal calderas

Understanding the processes that govern the inter-eruptive dynamics of volcanic calderas (e.g., Campi Flegrei, Yellowstone) is crucial to detect unrest and better forecast their activity. This is an important concern to monitoring agencies because calderas may represent major hazards to modern societies, both at local and global scale. One of the most intriguing caldera-related phenomena is the so-called breathing, i.e., continuous inflation-deflation cycles on the order of up to 10s of centimeters per year and with characteristic periodicities ranging from a few years to decades. In this study, we explore the breathing activity of Domuyo volcano (Argentina), a dacitic-rhyolitic caldera in the Southern Andes whose most recent eruption occurred >10,000 years ago (Lundgren et al., 2020); and the recent breathing phase leading to the moderate (volcano explosivity index 3) eruption in January 2020 at Taal volcano (Philippines). In particular, we integrate geodetic data (retrieved from the synthetic aperture radar -SAR- sensors onboard ALOS, ALOS-2, Radarsat-2, and Sentinel-1 satellites) with a recently discovered observable found to emerge on active volcanoes during unrest (Girona et al., 2021): low-temperature (~1 K over ambient temperature), large-scale (up to 10s of km²), long-term ( 6 months/1 year) thermal anomalies (retrieved from the moderate resolution imaging spectroradiometers -MODIS- onboard NASA’s Terra and Aqua satellites). Our analysis shows that geodetic and thermal unrest are significantly correlated, although the time series are phase shifted. To interpret these phase shifts and their implications, we develop a first-order, 1D numerical model based on mass, momentum, and energy conservation that couples the permeable flow of gases through the shallow crust, the viscoelastic deformation of the crust, the condensation of magmatic water vapor in the subsurface, and the diffusive transport of heat to the surface. Our preliminary results show that: (i) phase shifts between thermal and geodetic time series are controlled by detection limits, and by the coupling between magma reservoir processes and the transport of gas and heat through the crust; (ii) the pressure inside magma reservoirs can oscillate spontaneously during quiescent outgassing at the typical breathing timescales, thus suggesting that some geodetic and thermal unrest episodes are not necessarily associated to new magma inputs, but to the intrinsic dynamics of active magma reservoirs. This study has important implications for assessing volcanic hazards through improved eruption forecasting methods.

Girona, T., Realmuto, V. & Lundgren, P. Large-scale thermal unrest of volcanoes for years prior to eruption. Nat. Geosci. 14, 238–241 (2021). https://doi.org/10.1038/s41561-021-00705-4.

Lundgren, P., Girona, T., Bato, M.G. et al. The dynamics of large silicic systems from satellite remote sensing observations: the intriguing case of Domuyo volcano, Argentina. Sci Rep 10, 11642 (2020). https://doi.org/10.1038/s41598-020-67982-8.