Thermomechanical stress–strain numerical modelling of deglaciation since the Last Glacial Maximum in the Adamello Group (Rhaetian Alps, Italy)

Abstract

Deglaciated areas in the valleys of the Italian Alps have recently exhibited a high potential for geomorphologic hazards from diffuse deep-seated gravitational deformations (DSGSDs), caused by rock-mass creep processes that can evolve into rock falls and rock avalanches. A multidisciplinary approach that integrated geomorphologic surveys and stress–strain numerical simulations was used to investigate the effects of the stress release that was induced by the Last Glacial Maximum (LGM) in the Adamè Valley (Italian Alps). No evidence of DSGSDs has been found in this area; however, data are available to develop a well-constrained evolutionary model of the valley deglaciation. The extent and thickness of the southern extension of the Adamello glacier (the widest glacier in Italy) during its primary growth phases, including those of the LGM, three Late Glacial stages and the Little Ice Age (LIA) were reconstructed using glacial geological surveys and were reproduced using a finite-difference stress–strain sequential model spanning from the LGM to the present. A thermomechanical numerical configuration was developed based on geomechanical field measurements that were collected from rock outcrops and data from laboratory tests, specifically performed on intact rock samples. The numerical simulations demonstrate that thermomechanical viscous behaviour cannot be neglected because the resulting strains on the slopes are significantly higher than those resulting from conventional elastoplastic behaviour. The last major thermal effect in the rock masses reproduced using the model occurred from 11.5ka until the LIA; the resulting displacement rates are as much as several tens of mm/ka, which are consistent with the absence of DSGSDs in the Adamè Valley, as these rates are significantly lower than those previously obtained from DSGSDs and other large landslides in the Alps. Based on thermomechanical numerical solutions, these rates should persist for the next 1000years assuming that no variations in current climatic conditions occur.