MODELING DRIFT NOSES, AN UNCOMMON FORM OF DRUMLIN

Drumlins and related streamlined subglacial features (e.g. flutes, drift drumlins, roches moutonees, whalebacks, rock-cored drumlins, and crag & tails) have had innumerable papers written on their possible origins. Mentioned briefly by Boulton (1987), drift-nosed drumlins are landforms that have received relatively little attention. Examples of these features can be found on the Belcher Islands in Hudson Bay, Nunavut, Canada; based on this location Boulton (1987) argued that the drift noses occur where a bedrock scarp blocked the passage of the drift mass. We apply the term drift noses to similar features found in Clarks Fork Valley, northwestern Wyoming, and in south-central Sweden. All three locations had ice at least 1 km thick. In Wyoming drift noses composed of lodgment till lie on the stoss sides of resistant granitic outcrops. Many drift noses, long rock-cored drumlins, and crag & tails occur in Sweden where individual rock cores are at the stoss ends, the centers, or the lee ends of the features. We attempted physical modeling of these features using a wooden box (our glacial trough) with water- saturated sediment and a small heated copper obstacle on the bottom. For sediment we used Palouse loess (mostly silt) or Vashon lodgment till (with pebbles removed). A groove formed on the bottom of a block of ice (our glacier) as it was shoved past the “bedrock” obstacle. Although no significant drift noses formed, crag & tails developed downglacier of the obstacle, apparently by water-saturated sediment flowing into the groove on the bottom of the glacier. Our only “drift nose” formed as modeling clay was shoved past the obstacle; this suggests that viscosity and/or cohesion may be significant factors controlling the formation of drift noses. We could not determine what other factors might be important; possibilities include water content of the drift, particle size, ice temperature and velocity, size and shape of the bedrock obstacle.