Cooling‐dominated cracking in thermally stressed volcanic rocks

Abstract

Most studies of thermally induced cracking in rocks have focused on the generation of cracks formed during heating and thermal expansion. Both the nature and the mechanism of crack formation during cooling are hypothesized to be different from those formed during heating. We present in situ acoustic emission data recorded as a proxy for crack damage evolution in a series of heating and cooling experiments on samples of basalt and dacite. Results show that both the rate and the energy of acoustic emission are consistently much higher during cooling than during heating. Seismic velocity comparisons and crack morphology analysis of our heated and cooled samples support the contemporaneous acoustic emission data and also indicate that thermal cracking is largely isotropic. These new data are important for assessing the contribution of cooling‐induced damage within volcanic structures and layers such as dikes, sills, and lava flows.

Increasing the Permeability of Hydrothermally Altered Andesite by Transitory Heating

“…Nonetheless, we observe that the physical properties of moderately and highly altered Rotokawa andesite change after exposure to temperatures as low as 350 °C and that temperature increase consistently results in an increase in porosity (Table ). We attribute the observed porosity and permeability increase to a combination of mineralogical breakdown of clinochlore, quartz, and calcite and to microcracking resulting from inevitable small stresses induced by thermal gradients and reaction driven‐volume changes during both heating and cooling (Browning et al, ; Eggertsson et al, ; Ryan & Sammis, ; Heap, Lavallée, et al, ; Lamur et al, ; Vinciguerra et al, ). In addition, the altered samples are heterogeneous and crystalline, and the assumptions used to calculate the appropriate heating and cooling rate may, therefore, lead to overestimation.…”

“…This is especially important in a geological context where rocks may be subjected to microcracking imparted by strong temperature fluctuations and/or gradients (e.g., magmatic dike emplacement, contact metamorphism, cooling of magma bodies; Siratovich, Villeneuve, et al, , and references therein). Thermal treatment of rock cores conducted in an oven (heating all sides of a sample) has been shown to generate microcracks without preferred orientation, resulting in isotropic elastic wave velocities (e.g., Heap, Lavallée, et al, ; Heap, Baud, et al, ; Browning et al, ; Fortin et al, ; Siratovich et al, ; Vinciguerra et al, ). Browning et al () also suggest that cooling‐driven fracturing dominates over heating‐driven fracturing, which is likely in our experiments (wherein our cooling rates are similar to our heating rates).…”

“…As rocks are weaker in tension than compression (e.g., Harnett et al, ), cooling may be more likely to induce thermal fractures than heating (for comparable rates of temperature changes in our experiments, cf. Browning et al, ; Heap, Lavallée, et al, ; Schaefer et al, ), especially with higher cooling rates as can be induced by ingress of cooler water (e.g., Eggertsson et al, ; Siratovich, Villeneuve, et al, ; Villeneuve & Siratovich, ). Yet the microstructure of rocks is central to the development of thermal fractures (at the laboratory scale), as they favorably develop in intact material originally containing few fractures; if fractures are, however, initially abundant in a material, the propensity of the material to thermally fracture lessens (e.g., Eggertsson et al, ).…”

“…The effects of temperature on the physical, chemical, and mineralogical properties of volcanic rocks has been the subject of a range of studies (e.g., Björnsson, ; Browning et al, ; Kitao et al, ; Siratovich, Villeneuve, et al, ,Siratovich, von Aulock, et al, ), but the range of scenarios (e.g., heating vs. cooling), conditions (e.g., magnitude of temperature fluctuations), and reservoir rock types (e.g., unaltered versus altered) has prevented the generalization of the impact on the resultant reservoir rock permeability. For instance, cooling results in contraction, which may generate macroscopic thermal cracks to promote fluid flow (Lamur et al, ), yet it may also precipitate secondary mineralization that can, through time, block otherwise permeable pathways (Heap et al, ).…”

Viscoelastic Modeling of Nocturnal Thermal Fracturing in a Himalayan Debris‐Covered Glacier

“…In particular, the ice strength is smaller in tension and larger in compression (Petrovic, ). Ice cracking is therefore more likely to occur in tension, as is the case in many other geomaterials (e.g., Browning et al, ). Accordingly, the tensile stress of ice is the main focus of this study.…”