HR: 08:15h
AN: C51C-02 INVITED    [Abstracts]
TI: Physical Modelling of Rock Heave and Fracture by ice Segregation
AU: * Murton, J B
EM: j.b.murton@sussex.ac.uk
AF: University of Sussex, Department of Geography, Brighton, BN1 9QJ, United Kingdom
AB: The volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in polar and alpine regions. Physical modelling experiments that simulated natural freezing regimes in large blocks of chalk indicate that fracture results instead from ice segregation. This process was most pronounced in summer, as the rock active layer thawed, releasing meltwater that moved down into the underlying permafrost, where it supplied ice lenses that fractured the rock and heaved up the surface. Progressive heave was interrupted by the European heatwave of summer 2003, which triggered 10 mm settlement of the rock surface as ice lenses melted within the uppermost permafrost. During the following freeze-thaw cycles the ice lenses quickly started to grow again. After simulation of about 20 cycles of active-layer freezing and thawing, fractures in the artificial permafrost matched those in Arctic permafrost and ice-age weathering profiles in mid-latitude Europe. This agreement supports a conceptual model in which ice segregation in near-surface permafrost leads progressively to rock fracture and heave, whereas active-layer deepening leads episodically to melt of segregated ice and rock settlement. Fractured limestones, shales and clays in southern England suggest that ice segregation has been a key driver of landscape evolution during Pleistocene periglacial episodes.
DE: 0702 Permafrost (0475)
DE: 0710 Periglacial processes
DE: 0774 Dynamics
DE: 0790 Weathering (1625, 1886)
DE: 0798 Modeling
SC: Cryosphere [C]
MN: 2007 Fall Meeting