Bed Roughness Beneath the Greenland Ice Sheet

TY - JOUR

T1 - Bed Roughness Beneath the Greenland Ice Sheet

AU - Rippin, David

PY - 2013/8

Y1 - 2013/8

N2 - The roughness of the bed beneath ice streams exerts an important control on their dynamics. Here, the first in-depth analysis of the roughness of the topography beneath the Greenland Ice Sheet is presented. Much of the interior is underlain by a smooth bed, while the margins are characterized by high roughness – this is particularly pronounced in the east where more mountainous topography dominates and fast-flow features are laterally constrained in deep narrow valleys. In contrast, fast-flow in the west is much less laterally constrained and similarly, areas of high roughness are less extensive and pronounced. It is also proposed that there is a major geological control on the distribution of bed variability. A significant thrust-fault has been identified which coincides approximately with the boundary between the very rough bed in the east and the smooth central region. Furthermore there is an abrupt change in roughness approximately coinciding with the crossing of this fault line. This suggests a significant limiting factor on the extent of fast flow in the east, which is lacking in the west where there are less marked controls. The small size of many glaciers draining Greenland make their local bed conditions difficult to ascertain with great confidence. Nevertheless, Petermann Glacier is quite different. Its size means it is possible to ascertain that it lies in an exceptionally well-pronounced and deep trough which is characterized by an extensive smooth bed. This smooth bed extends some considerable distance into the ice-sheet with little evidence of any substantial basal control. We hypothesize that in line with findings from Antarctica, the smooth bed may be due to the presence of deformable marine sediments which facilitates faster flow, although smoothing may also be a result of ice dynamics and subglacial erosion. The fact that the smooth bed of Petermann Glacier extends some considerable distance raises concerns about possible stability of this feature, and perhaps others in Greenland too.

AB - The roughness of the bed beneath ice streams exerts an important control on their dynamics. Here, the first in-depth analysis of the roughness of the topography beneath the Greenland Ice Sheet is presented. Much of the interior is underlain by a smooth bed, while the margins are characterized by high roughness – this is particularly pronounced in the east where more mountainous topography dominates and fast-flow features are laterally constrained in deep narrow valleys. In contrast, fast-flow in the west is much less laterally constrained and similarly, areas of high roughness are less extensive and pronounced. It is also proposed that there is a major geological control on the distribution of bed variability. A significant thrust-fault has been identified which coincides approximately with the boundary between the very rough bed in the east and the smooth central region. Furthermore there is an abrupt change in roughness approximately coinciding with the crossing of this fault line. This suggests a significant limiting factor on the extent of fast flow in the east, which is lacking in the west where there are less marked controls. The small size of many glaciers draining Greenland make their local bed conditions difficult to ascertain with great confidence. Nevertheless, Petermann Glacier is quite different. Its size means it is possible to ascertain that it lies in an exceptionally well-pronounced and deep trough which is characterized by an extensive smooth bed. This smooth bed extends some considerable distance into the ice-sheet with little evidence of any substantial basal control. We hypothesize that in line with findings from Antarctica, the smooth bed may be due to the presence of deformable marine sediments which facilitates faster flow, although smoothing may also be a result of ice dynamics and subglacial erosion. The fact that the smooth bed of Petermann Glacier extends some considerable distance raises concerns about possible stability of this feature, and perhaps others in Greenland too.

U2 - 10.3189/2013JoG12J212

DO - 10.3189/2013JoG12J212

M3 - Article

SN - 0022-1430

VL - 59

SP - 724

EP - 732

JO - Journal of Glaciology

JF - Journal of Glaciology

IS - 216

ER -