TY - JOUR

T1 - Grevasse patterns and the strain-rate tensor

T2 - A high-resolution comparison

AU - Harper, J. T.

AU - Humphrey, N. F.

AU - Pfeffer, W. T.

PY - 1998

Y1 - 1998

N2 - Values of the strain-rate tensor represented at a 20 m length scale are found to explain the pattern and orientation of crevasses in a 0.13 km2 reach oHVorthington Glacier, Alaska, U.S.A. The flow field of the reach is constructed from surveyed displacements of 110 markers spaced 20-30 m apart. A velocity gradient method is then used to calculate values of the principal strain-rate axes at the nodes of a 20 m × 20 m orthogonal grid. Crevasses in the study reach are of two types, splaying and transverse, and are everywhere normal to the trajectories of greatest (most tensile) principal strain rate. Splaying crevasses exist where the longitudinal strain rate (ε̇x) is < 0 and transverse crevasses are present under longitudinally extending flow (i.e. ε̇x > 0). The orientation of crevasses changes in the down-glacier direction, but the calculated rotation by the flow field does not account for this change in orientation. Observations suggest that individual crevasses represent local values of the regional flow field and are transient on the time-scale of 1-2 years; they are not persistent features that are translated and rotated by flow. Crevasse patterns are thus found to be a useful tool for mapping the strain-rate tensor in this reach of a temperate valley glacier.

AB - Values of the strain-rate tensor represented at a 20 m length scale are found to explain the pattern and orientation of crevasses in a 0.13 km2 reach oHVorthington Glacier, Alaska, U.S.A. The flow field of the reach is constructed from surveyed displacements of 110 markers spaced 20-30 m apart. A velocity gradient method is then used to calculate values of the principal strain-rate axes at the nodes of a 20 m × 20 m orthogonal grid. Crevasses in the study reach are of two types, splaying and transverse, and are everywhere normal to the trajectories of greatest (most tensile) principal strain rate. Splaying crevasses exist where the longitudinal strain rate (ε̇x) is < 0 and transverse crevasses are present under longitudinally extending flow (i.e. ε̇x > 0). The orientation of crevasses changes in the down-glacier direction, but the calculated rotation by the flow field does not account for this change in orientation. Observations suggest that individual crevasses represent local values of the regional flow field and are transient on the time-scale of 1-2 years; they are not persistent features that are translated and rotated by flow. Crevasse patterns are thus found to be a useful tool for mapping the strain-rate tensor in this reach of a temperate valley glacier.

UR - http://www.scopus.com/inward/record.url?scp=0031785223&partnerID=8YFLogxK

U2 - 10.1017/s0022143000002367

DO - 10.1017/s0022143000002367

M3 - Article

AN - SCOPUS:0031785223

SN - 0022-1430

VL - 44

SP - 68

EP - 76

JO - Journal of Glaciology

JF - Journal of Glaciology

IS - 146

ER -