While the final manifestations of caldera-forming eruptions can be easily observed on the Earth’s surface and are thus relatively well studied, the physical conditions and causes of caldera collapse and the mechanisms of brittle failure of the underlying rocks are still a mystery. The aim of a long-standing project by a joint team from the Faculty of Science of the UK and the Czech Technical University in Prague was to understand under what conditions the gravitational collapse of calderas occurs and what effect the shape of the underlying magma mantle, its size and depth in the Earth’s crust has. New research has shown, using a combination of geological data and mathematical modelling, that magma pressure oscillations lead to intense brittle failure in places, and therefore to a reduction in the strength of the magma crust ceiling, but that collapse and caldera formation can only occur under specific conditions.

Somr M., Žák J., Kabele P., Tomek F. (2023): Analysis of fracturing processes leading to caldera collapse. Earth-Science Reviews 241, 104413 (DOI)

Evaporation from rocks is a poorly understood, yet important process. In the recent study, an evaporation rate from 10 lithologies, including sedimentary, igneous, and metamorphic granular rocks, was measured and calculated. The measured evaporation rate varied over four orders of magnitude (0.4–2447 mm/year), and the calculations reasonably followed the measured values. Within the range of observed values, the evaporation rate was mostly influenced by the vaporization plane depth below the rock surface (by up to 2.2 orders of magnitude), which was followed by: lithology (up to 1.1 order of magnitude), local climate (up to 1.0 order of magnitude), and climate seasonality (up to 0.8 order of magnitude). Thus, our study shows the key role of the vaporization plane depth in the evaporation rate. This approach can find employment in a large number of investigations such as in the evaporation estimates and hydrologic balance in rock landforms and rocky slopes, hydrologic processes in the shallow rock subsurface, living conditions of endolithic and epilithic organisms, weathering processes, and in the protection of carved or rock constructed cultural heritage.

Slavík M., Bruthans J., Schweigstillová J. (2018): Evaporation rate from surfaces of various granular rocks: Comparison of measured and calculated values. Science of the Total Environment 856, 159114. (DOI)

Cobalt is one of the most important critical metals which could be potentially extracted from the old metallurgical slags in the Zambian Copperbelt. The slags from Luanshya, the oldest mining and smelting site in the Copperbelt, contain up to 5990 ppm Co (median: 2370 ppm). The detailed mineralogical investigation combined with the sulfuric acid leaching simulating hydrometallurgical recovery indicated that up to 67% of Co can be extracted from slag in a short period of time (24 h). However, despite the dramatic increase of Co prices on the global market, its recovery from the Luanshya slags appears to be non-economical due to the high costs of the mechanical and chemical processing of the slag materials. The paper is freely available via open access:

Ettler V., Mihaljevič M., Drahota P., Kříbek B., Nyambe I., Vaněk A., Penížek V., Sracek O., Natherová V. (2022): Cobalt-bearing copper slags from Luanshya (Zambian Copperbelt): Mineralogy, geochemistry, and potential recovery of critical metals. Journal of Geochemical Exploration 237, 106987. (DOI)