Item: Release and motion of arctic slushflows
Title: Release and motion of arctic slushflows
Proceedings: Proceedings of the 1982 International Snow Science Workshop, Bozeman, Montana, USA
Authors: Arthur Mears, National Hazard Consultant, 222 E. Gothic Ave., Gunnison, Colorado 81230
Abstract: Two types of slushflows studied during the spring of 1981 and 1982 in the Philip Smith Mountains, central Brooks Range, Alaska, were (l) point failures of water-saturated snow in wide gullies of less than 10° gradient, and (2) slab, or "plug," releases in constricted 15° to 20° gullies. The plug-release slushflows were the larger, more energetic and potentially destructive form. Plug fracture boundaries consisted of a proximal crown, distal stauchwall, lateral flanks, and a bed surface· within a rapidly discharging snowmelt-runoff stream. Crown surfaces were 2.7 to 6.6 m thick, 10 to 18 m wide, and 590 to 710 kg/m3 density. The crown-to-stauchwall distance was 40 to 60 m, and plug volumes ranged from 1000 to 5000 m3. After release, the plug quickly liquefied and slid up over the stauchwall. Rapid acceleration would follow on slopes of 10° to 15° as the plug entrained nearly all of the snow, stream water, and a considerable rock load estimated as 10 to 15% of the slushflow volume. In some cases, entrained boulders, more than 2 m long, were transported to the distal margin of the flow, more than 1 km from the crown. Slushflow mass would increase quickly; the final volume of the flow would be roughly 10 times the released plug volume, but at any instant the moving mass would be confmed to less than 10% of the total path length. Velocities observed in two moderate-sized flows were 15 to 20 m/s. Indirect methods used to compute velocities of two very large 1982 slushflows include (1) energy calculations at an adverse slope runup, (2) application of a rigid-block model with a constant friction coefficient equal to the tangent of the mean path slope (tan ex), and (3) application of a two-component model assuming a constant sliding friction coefficient less than tan ex and an inertial velocity squared term. All three methods yield maximum velocities of 23 to 25 m/s for the two large 1982 flows. Large slushflows had ex - angles of 7° to 9°, approximately half the ex - angles of the flattest snow avalanches. Large alluvial deposits produced by slushflows are as' much as 800 m long with mean gradients of 5° to 6°. These deposits are widespread throughout Brooks Range valleys and attest to the importance of slushflows as an Arctic erosion process.
Keywords: slushflow, runoff,
Digital Abstract Not Available