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Silicic caldera volcanoes present major volcanic and seismic hazards but also host dynamic hydrothermal and groundwater systems and a rich but largely unexplored subsurface biosphere. Many of these volcanoes are hosted in rift settings. The intricate connections and feedbacks among magmatism, rifting, hydrothermal processes, and the biosphere in these complex systems remain poorly understood, necessitating subsurface joint observations that are only enabled by scientific drilling. The CALDERA (Connections Among Life, geo-Dynamics and Eruptions in a Rifting Arc caldera) project workshop funded by the International Continental Scientific Drilling Program (ICDP) gathered multi-disciplinary international experts in January 2023 to advance planning of a scientific drilling project within one of these dynamic, rift-hosted calderas, the Okataina Volcanic Centre (OVC), Aotearoa New Zealand. The OVC's high eruption rate, frequent unrest events and earthquake swarms, location in a densely faulted rapidly extending rift, abundant groundwater–geothermal fluid circulations, and diverse surface hot spring microbiota make it an ideal location for exploring a connected geo-hydro-biosphere via scientific drilling and developing a test bed for novel volcano monitoring approaches. Drilling configurations with at least two boreholes (∼ 200 and ∼ 1000–1500 m deep) were favoured to achieve the multi-disciplinary objectives of the CALDERA project. Decadal monitoring including biosphere activity and composition has the potential to evaluate the response of the hydro-bio system to volcano-tectonic activity. In addition to the OVC caldera-scale datasets already available, site surveys will be conducted to select the best drilling locations. The CALDERA project at the OVC would provide, for the first time, an understanding of volcanic–tectonic–hydrological–biological connections in a caldera–rift system and a baseline for global comparisons with other volcanoes, rifts, and hydrothermal systems. CALDERA would serve as an unprecedented model system to understand how and how quickly the subsurface biosphere responds to geologic activities. Discoveries will improve assessment of volcanic and seismic hazards, guide the sustainable management and/or conservation of groundwater and geothermal resources and microbial ecosystems, and provide a forum for interweaving mātauranga Māori and Western knowledge systems. [ABSTRACT FROM AUTHOR]

Rocks commonly display a reduction in elastic modulus during an acoustic perturbation followed by a logarithmic recovery of the modulus to its original value. This nonlinear elastic behavior can also be induced by changes in temperature of the rock, although experimental data for this are sparse. In this paper, we utilize temperature perturbations to broaden our understanding of the causes and mechanisms of nonlinear elasticity in rocks. We perform laboratory experiments tracking the nonlinear response of a Berea sandstone under vacuum both during and following 10°C changes in temperature. Ultrasonic velocity decreases by up to 0.30 ± 0.02% during both temperature increases and decreases, before recovering in the following days. Continuous monitoring over a 2‐month period also reveals a longer‐term 0.78 ± 0.04% increase in velocity. To explain these observations, we modify a recent model for nonlinear elasticity based on the shearing and subsequent recreation of internal microscopic contacts. Application of this model to our data suggests that internal stresses from differential thermal expansion/contraction of mineral grains break contacts, inducing nonlinear weakening. The degree of weakening depends on the temperature gradient. Slow dynamics recovery in the ∼10 hr following a temperature change likely results from the recreation of broken contacts due to nanoscopic adhesive forces. In contrast, the long‐term velocity increase results from evaporation of bound water from clay minerals. In addition to furthering our understanding of nonlinear elasticity in rocks, our results imply that sudden changes of temperature in shallow crustal environments will induce nonlinear weakening that persists for hours to days. Plain Language Summary: Rocks weaken when seismic waves travel through them, a phenomenon which may drive critically stressed rocks to failure. This weakening is not permanent, however, and the rock recovers its original strength in the following minutes, hours, or days. Such behavior can also occur when the temperature of the rock changes, although only a handful of laboratory studies investigating this behavior exist. In this study, we monitor the speed of an ultrasonic wave (a proxy for strength) through a sample of Berea sandstone during and after temperature changes of 10°C. We find that whenever the temperature increases or decreases, the wave speed decreases by up to 0.30% before recovering to the original value in the following hours. By modifying a recently developed model, we find that this behavior is caused by microscopic bonds in the rock breaking and reforming during and after a temperature change. Additionally, an overall 0.78% increase in wave speed over 2 months is caused by water molecules evaporating from clay minerals. The results of our study help us to understand why rocks show this unusual behavior, and imply that a change in temperature in the earth will weaken nearby rocks for a period of time. Key Points: We monitor nonlinear reduction and recovery of ultrasonic velocity in Berea sandstone caused by 10°C changes in temperatureUltrasonic velocity drops by ∼0.3% for both temperature increases and decreases before recovering in the following daysOur results and modeling emphasize that the rate of temperature change controls the magnitude of nonlinear weakening [ABSTRACT FROM AUTHOR]

This article introduces the role of rock physics in the energy transition challenge. Rock physics is essential for characterizing geological reservoirs, optimizing monitoring operations, interpreting data, and developing predictive models for extraction and injection activities. The article highlights the topics discussed at the 6th International Workshop in Rock Physics, which focused on energy transition and climate change mitigation. The special section includes five papers that demonstrate the potential of rock physics in meeting net-zero goals. The papers cover a range of topics, including frequency-dependent attenuation, physical and transport properties of salt rocks, denoising techniques for rock samples, anisotropy of coal seams, and seismic reflect coefficient inference. [Extracted from the article]