Premium
Experimental design for a pilot study on bedrock weathering near the permafrost table
Author(s) -
Murton Julian B.,
Coutard JeanPierre,
Lautridou JeanPierre,
Ozouf JeanClaude,
Robinson David A.,
Williams Rendel B.G.,
Guillemet Gerard,
Simmons Peter
Publication year - 2000
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/1096-9837(200011)25:12<1281::aid-esp137>3.0.co;2-u
Subject(s) - permafrost , geology , frost heaving , frost (temperature) , bedrock , active layer , frost weathering , aggradation , weathering , geotechnical engineering , geomorphology , hydrology (agriculture) , soil water , soil science , layer (electronics) , oceanography , chemistry , organic chemistry , structural basin , fluvial , thin film transistor
An experimental design is described to test the hypothesis that ice segregation near the top of permafrost and in the lower part of the active layer can brecciate frost‐susceptible bedrock. Seasonal temperature cycles in the active layer and the top of permafrost were simulated to a first approximation within a block of chalk measuring 0·30 m × 0·31 m wide and 0·33 m high and insulated around the sides to minimize lateral heat transfer. The block, moistened first by capillary rise, was initially frozen from the surface downwards, simulating permafrost aggradation. Thereafter, the upper half of the block was cycled above and below 0°C (simulating seasonal freezing and thawing of the active layer) while the lower half remained below 0°C (simulating permafrost). During thaw cycles water was supplied to the surface and base of the simulated active layer. Temperature, unfrozen water content, surface frost heave and porewater pressure within the chalk were monitored during the experiment. Preliminary data from three freeze–thaw cycles indicate that: (1) both downward and upward freezing occurred during freeze‐back of the simulated active layer; (2) 78 per cent of the surface frost heave (total = 4·8 mm) took place during the thaw periods, when the active layer was approaching or at its maximum depth; and (3) negative porewater pressure was recorded in some instances during freeze‐back, suggesting the occurrence of cryogenic suction. The thaw‐related frost heave suggests that ice segregation within the chalk occurred beneath the descending thawing front, in the still frozen part of the simulated active layer and the uppermost permafrost, and marked the commencement of rock brecciation. Copyright © 2000 John Wiley & Sons, Ltd.