GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 81-18
Presentation Time: 9:00 AM-5:30 PM


CARSON, Robert J.1, DOWLING, Thomas P.F.2, BAILEY, Madison1, BARTER, Weston V.B.1, COATES, Molly1, FINGER, Sarah1 and MORGAN, Silas1, (1)Department of Geology, Whitman College, 345 Boyer, Walla Walla, WA 99362, (2)Department of Geology, Lund University, Solvegatan 12, Lund, 223 62, Sweden,

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.
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