02150nas a2200157 4500008004100000245008400041210006900125300001200194490000800206520160400214653006201818100002101880700001901901700002001920856005201940 2003 eng d00aA Decade of Sedimentation in Ice-contact, Proglacial Lakes, Bering Glacier, AK.0 aDecade of Sedimentation in Icecontact Proglacial Lakes Bering Gl a309-3240 v1603 a

Bathymetric surveys during the 1991–2000 decade in two ice-contact, proglacial lakes on the eastern sector of Bering piedmont lobe captured the buildup effects of the 1993–1995 surge. Following ice-front advance of 1.0–1.5 km into Tsivat and Tsiu Lakes, the basins were significantly altered by surge-related sedimentation including the impact of a subglacial outburst into Tsivat Lake. The subsequent changes in basin shape, size, and morphology were monitored by six bathymetric surveys. Measured changes in water depth serve as a proxy for determining increments of sediment accumulation.

Upwelling, ice-front vents fed by subglacial tunnels transported suspended fine sediment directly into the lake system. The rate of suspension settling within both lakes varied from 0.6 to 1.2 m year−1 prior to the surge. Suspended load during surge years increased sixfold from 1.7 to 13.9 g l−1, accompanied by increased sediment accumulation of 2.2–3.1 m year−1. Vent-related aggradation and subsequent filling of Tsivat Lake caused sediment bypassing to Tsiu Lake, where encroachment by delta growth contributed to a postsurge rate of bottomset accumulation of 3.0 m year−1.

The total sediment influx from subglacial sources is represented by the sum of bathymetrically determined accumulation, plus an estimated volume of sediment that remained suspended, thus passing through the lake system. Total sediment flux along the eastern Bering piedmont lobe from 1991 to 2000 is approximately 227 million cubic meters.

10aIce-contact lake sedimentation; Bathymetry; Sediment flux1 aFleisher, P., J.1 aBailey, P., K.1 aCadwell, D., H. uhttp://dx.doi.org/10.1016/S0037-0738(03)00089-702447nas a2200205 4500008004100000245009300041210006900134300001200203490000800215520181900223653001102042653001902053653001202072653002302084653001002107100002102117700002002138700001902158856006402177 1998 eng d00aTsivat Basin Conduit System persists through two surges, Bering Piedmont Glacier, Alaska0 aTsivat Basin Conduit System persists through two surges Bering P a877-8870 v1103 a

The 1993–1995 surge of Bering Glacier, Alaska, occurred in two distinct phases. Phase 1 of the surge began on the eastern sector in July, 1993 and ended in July, 1994 after a powerful outburst of subglacial meltwater into Tsivat Lake basin on the north side of Weeping Peat Island. Within days, jökulhlaup discharge built a 1.5 km2 delta of ice blocks (25–30 m) buried in outwash. By late October 1994, discharge temporarily shifted to a vent on Weeping Peat Island, where a second smaller outburst dissected the island and built two new sandar. During phase 2, which began in spring 1995 and ended within five months, continuous discharge issued from several vents along the ice front on Weeping Peat Island before returning to the Tsivat Basin.

Surge-related changes include a five- to six-fold increase in meltwater turbidity; the redirection of supercooled water in two ice-contact lakes; and an increase in the rate of glaciolacustrine sedimentation. U.S. Geological Survey aerial photos by Austin Post show large ice blocks in braided channels indicating excessive subglacial discharge in a similar position adjacent to Weeping Peat Island during the 1966–1967 surge. During the subsequent three decades of retreat, the location of ice-marginal, subglacial discharge vents remained aligned on a linear trend that describes the position of a persistent subglacial conduit system. The presence of a major conduit system, possibly stabilized by subglacial bedrock topography, is suggested by (1) high-level subglacial meltwater venting along the northern side of Weeping Peat Island during the 1966–1967 surge, (2) persistent low-level discharge between surges, and (3) the recurrence of localizing meltwater outbursts associated with both phases of the 1993–1995 surge.

10aAlaska10aBering Glacier10aglacier10ameltwater turbidit10asurge1 aFleisher, P., J.1 aCadwell, D., H.1 aMuller, E., H. uhttp://bulletin.geoscienceworld.org/content/110/7/877.short