Glacial Maximum Deglaciation Research Articles

The Role of Temperature in the Stress–Strain Evolution of Alpine Rock-Slopes: Thermo-Mechanical Modelling of the Cimaganda Rockslide

AbstractIn this work, the thermo-mechanical stress–strain history of an Alpine slope is analyzed, with particular focus on the historical Cimaganda large landslide (Sondrio Province, Italy), which mobilized an estimated volume of 7.5 mm3 of rock material. Accurate geomorphological and geomechanical characterization involving field surveys and laboratory testing was carried out, leading to the development of a conceptual model of the slope. A thermo-mechanical semi-coupled approach was developed, considering both glacial debuttressing and thermo-mechanical effects due to gradual exposure of the slope to atmospheric conditions and paleo-temperature redistribution resulting from the Last Glacial Maximum deglaciation. A 2D distinct-element numerical approach was adopted, supported by a 2D finite-element analysis to simulate heat diffusion over the Valley cross-section. Modelling results allow to simulate the general evolution of the Cimaganda rock-slope and to highlight the significance of thermal processes in preparing rock-slope instabilities. While the mechanical effect of ice thickness reduction alone brings about moderate rock mass damage, the introduction of temperature couplings results in a substantial increase of damage, representing a significant factor controlling the stress–strain evolution of the slope. Simulated displacement and the development of a deep region of shear strain localization at a depth roughly corresponding to that of the detected Cimaganda sliding surface, allow to highlight the significance of temperature influence in preparing the rock-slope to instability.

Rapid Last Glacial Maximum deglaciation in the Indian Himalaya coeval with midlatitude glaciers: New insights from 10Be‐dating of ice‐polished bedrock surfaces in the Chandra Valley, NW Himalaya

AbstractDespite a large number of dated glacial landforms in the Himalaya, the ice extent during the global Last Glacial Maximum (LGM) from 19 to 23 ka is only known to first order. New cosmogenic 10Be exposure ages from well‐preserved glacially polished surfaces, combined with published data, and an improved production rate scaling model allow reconstruction of the LGM ice extent and subsequent deglaciation in the Chandra Valley of NW India. We show that a >1000 m thick valley glacier retreated >150 km within a few thousand years after the onset of LGM deglaciation. By comparing the recession of the Chandra Valley Glacier and other Himalayan glaciers with those of Northern and Southern Hemisphere glaciers, we demonstrate that post‐LGM deglaciation was similar and nearly finished prior to the Bølling/Allerød interstadial. Our study supports the view that many Himalayan glaciers advanced during the LGM, likely in response to global variations in temperature.

Paleoceanographic control on a large marine reservoir effect offshore of Tokai, south of Japan, NW Pacific, during the last glacial maximum-deglaciation

Knowledge of the marine reservoir effect is important in calibrating radiocarbon ages to calendar ages, and in correlating geologic and paleoceanographic events among different sites, including global events. Large, explosive volcanic eruptions have yielded numerous volcanic ash layers (tephras) over geological time. Because tephra layers are deposited both on land and upon the seafloor, they represent a unique and important link between the geological records of terrestrial and marine areas. Comparison of the radiocarbon ages of a tephra layer deposited in marine (planktonic foraminifera) and terrestrial (peat) materials reveals a local marine reservoir age (600–700 years or more) during the early part of the last deglaciation off Tokai, south of Japan. This age is larger than that determined for the present-day Pacific coast of Japan (82 years) and similar to that of the present-day subarctic NW Pacific (350–580 years). This difference between modern-day and deglaciation marine reservoir values is thought to reflect the contrasting properties of surface water masses between the two periods.