Thermomechanical Stresses Drive Damage of Alpine Valley Rock Walls During Repeat Glacial Cycles

• Published in: Journal of geophysical research. Earth surface Vol. 123; no. 10; pp. 2620 - 2646
• Main Authors: Grämiger, Lorenz M., Moore, Jeffrey R., Gischig, Valentin S., Loew, Simon
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-10-2018
• Subjects: Annual cycles; Annual temperatures; Bedrock; Boundary conditions; Computer simulation; Contraction; Cooling effects; Cycles; Damage; debuttressing; Deglaciation; Glacial advances; glacial cycles; Glaciation; Glacier ice; Glaciers; Glaciology; Great Aletsch Glacier; Holocene; Ice; Ice loads; Instability; Loads (forces); Mathematical models; Meltwater; Numerical models; paraglacial rock slope failures; Pleistocene; Rock masses; Rocks; Slope; Slope stability; Slopes; Stresses; Surface temperature; Switzerland; Temperate glaciers; Temperature; Temperature changes; Temperature cycles; Temperature distribution; Temperature effects; Temperature fields; Thermal shock; Thermomechanical analysis; thermomechanics; Unloading; Valleys; Walls
• ISSN: 2169-9003; 2169-9011
• DOI: 10.1029/2018JF004626

Cycles of glaciation alter the temperature field in proximal alpine valley flanks, driving rock slope damage through thermomechanical stresses. Here we extend simplified assumptions of glacial debuttressing to quantitatively examine how paraglacial bedrock temperature changes, acting in concert with changing ice loads during Late Pleistocene and Holocene glacial cycles, create damage in adjacent rock slopes and prepare future slope instabilities. When in contact with temperate glacier ice, valley walls maintain near isothermal ~0 °C surface temperatures and are shielded from daily and annual cycles. With retreat, rock walls are rapidly exposed to strongly varying temperature boundary conditions, a transition we term “paraglacial thermal shock.” Using detailed, conceptual numerical models based on the Aletsch Glacier in Switzerland, we show that including thermomechanical stresses during simulated glacial cycles creates significantly more rock slope damage than predicted for purely mechanical ice loading and unloading. Glacier advances are especially effective in generating damage as rapid cooling drives contraction of the rock mass reducing joint normal stresses. First time exposure to annual temperature cycles during deglaciation induces a shallow damage front that follows the retreating ice margin, generating damage in a complementary process at shorter time scales. Acting on a reduced strength rock mass, modeled thermomechanical cycles enhance the development of a slope instability with similar attributes as observed in our study area. Our results demonstrate that thermomechanical stresses acting in conjunction with changing ice loads are capable of generating considerable rock slope damage with spatial and temporal patterns controlled by glacier extents.
Key Points
Subsurface temperature changes on glacial time scales can generate rock mass damage through thermomechanical coupled stresses
Glacier advances are most effective in producing rock slope damage as cooling drives contraction of subglacial bedrock
Thermal shock during deglaciation creates a shallow damage front as bedrock is first exposed to annual temperature cycles