Tsivat basin conduit system persists through two surges, Bering Piedmont glacier, Alaska

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 Feat Island. Within days, jokulhlaup discharge built a 1.5 km(2) delta of ice blocks (25-30 m) buried in outwash, By late October 1994, discharge temporarily shifted to a vent on Weeping Feat 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 Feat 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 Feat 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 Feat 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.