In nature, sub-surface bodies of molten or ductile rock might become abruptly depleted, resulting in the collapse of the overlying rock and the sometimes catastrophic formation of a "hole in the ground" at surface.
These are termed sinkholes in karst terrains and pit-craters or calderas on volcanoes. For the first time, S. Poppe and colleagues use computed X-ray micro-tomography (μCT), similar to the imaging of patients using CT-scanners, to image laboratory-scale models of such collapse process.
Their simulations illustrate how collapse rates within the collapsing rock are varying in space and time, with the highest rates before and shortly after the surface depression is formed. The collapsing material also undergoes a volumetric expansion. On volcanoes, such "bulking" of the rocks overlying an emptying magma chamber may at least partially explain why the volume of the erupted lava is commonly larger compared to that of the surface depression.
This insight is of great use to seismic or volcano observatories who will face such collapse events in the future.
Sinkholes, pit craters, and small calderas: Analog models of depletion-induced collapse analyzed by computed X-ray microtomography S. Poppe et al., Dept. of Geography, Earth System Science, Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussels, Belgium. Published online 26 Aug. 2014; http://dx.doi.org/10.1130/B30989.1.