|
Permafrost and Frozen Ground |
1 School of Earth, Ocean and Planetary Sciences, Cardiff University, Cardiff CF10 3YE, UK harrisc{at}cardiff.ac.uk
2 Department of Geography, University of Sussex, Brighton BN1 9QJ, UK
In six experiments, model ice wedges 150 mm high and
50 mm wide were thawed from the surface downward at 30g in a geotechnical centrifuge, simulating ice-wedge casting during progressive active-layer deepening through permafrost. The frozen host soils ranged from sand to silt to clayey silt. Resulting ice-wedge pseudomorphs indicated that the degree of deformation during casting was determined by factors that control thaw consolidation. Hence, deformation increased as the host sediments became finer-grained and more ice-rich. Thaw of host sand at 15 and 20% gravimetric ice content and host silt at 20 and 40% ice content resulted in the formation of partially-developed ice-wedge pseudomorphs with an upper ‘plug’ of sediment derived largely from the cover soil, a central tunnel and a basal plug of sediment. Thaw of host clayey silt at 30 and 60% ice content resulted in the formation of fully developed pseudomorphs that were significantly narrower and shorter than the initial ice wedges. The experiments support the hypothesis that ice-wedge pseudomorphs tend to be better preserved in coarser-grained sediments that are not ice-rich and therefore deform little during thaw of constituent ice wedges. This selective preservation has probably led to underestimation of ice-wedge pseudomorphs in fine-grained soils that were originally ice-rich and therefore a bias towards reconstructing cold temperatures.
This article has been cited by other articles:
 |
|
 |
|
  C. Harris and J. B. Murton Interactions between glaciers and permafrost: an introduction Geological Society, London, Special Publications, 2005; 242: 1 - 9. [Abstract] [PDF]
|
|
