Abstract
AbstractThe current paper studies the dynamics and age of the Triangle du Tacul (TDT) ice apron, a massive ice volume lying on a steep high-mountain rock wall in the French side of the Mont-Blanc massif at an altitude close to 3640 m a.s.l. Three 60 cm long ice cores were drilled to bedrock (i.e. the rock wall) in 2018 and 2019 at the TDT ice apron. Texture (microstructure and lattice-preferred orientation, LPO) analyses were performed on one core. The two remaining cores were used for radiocarbon dating of the particulate organic carbon fraction (three samples in total). Microstructure and LPO do not substantially vary with along the axis of the ice core. Throughout the core, irregularly shaped grains, associated with strain-induced grain boundary migration and strong single maximum LPO, were observed. Measurements indicate that at the TDT ice deforms under a low strain-rate simple shear regime, with a shear plane parallel to the surface slope of the ice apron. Dynamic recrystallization stands out as the major mechanism for grain growth. Micro-radiocarbon dating indicates that the TDT ice becomes older with depth perpendicular to the ice surface. We observed ice ages older than 600 year BP and at the base of the lowest 30 cm older than 3000 years.
Highlights
Ice aprons, known as ice faces (Gruber and Haeberli, 2007; Hasler and others, 2011), are scarce accumulations of massive ice found in glacierized basins, above the equilibrium line (Armstrong and Roberts, 1956; Bhutiyani, 2011; Cogley and others, 2011; Guillet and Ravanel, 2020)
Our results showed that the ice composing the Triangle du Tacul (TDT) ice apron mainly deforms under a low-strain rate simple shear stationary regime and that deformation is rather homogeneous along the axis of the core
We presented texture analysis and microradiocarbon dating of cores collected on the TDT ice apron
Summary
Known as ice faces (Gruber and Haeberli, 2007; Hasler and others, 2011), are scarce accumulations of massive ice found in glacierized basins, above the equilibrium line (Armstrong and Roberts, 1956; Bhutiyani, 2011; Cogley and others, 2011; Guillet and Ravanel, 2020) Such a definition typically encompasses ice masses from different settings like isolated massive ice patches on rock walls (e.g. north face of Mount Alberta, Canadian Rocky Mountains) or any steep ice body lying over a glacial bergschrund, defined by Cogley and others (2011) as ‘a crevasse at the head of a glacier that separates flowing ice from stagnant ice, or from a rock headwall’ (e.g. the Triangle du Tacul ice apron, Mont-Blanc massif, cf Section 2.1, see Guillet and Ravanel (2020) for more details). The disintegration of ice aprons would lead to an important loss in European alpine culture heritage
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