Thermokarst Lakes on the Arctic Coastal Plain of Alaska: Geomorphic Controls on Bathymetry

Abstract

ABSTRACTDetailed bathymetric data were collected for 28 thermokarst lakes across the Arctic Coastal Plain (ACP) of northern Alaska from areas with distinctly different surficial sediments and topography. Lakes found in the low‐relief coastal area have developed in marine silts that are ice‐rich in the upper 6–10 m. The lakes tend to be shallow (~ 2 m), of uniform depth and lack prominent littoral shelves. Further inland on the ACP, lakes have formed in relatively ice‐poor aeolian sand deposits. In this hilly terrain, average lake depth is less (~ 1 m) despite deeper (3–5 m) central pools. This bathymetry reflects the influence of broad, shallow littoral shelves where sand, eroded from bluffs at the lake margin, is deposited concurrently with deep penetration of the talik beneath the basin centre. Lakes in the ACP‐Arctic Foothills transition zone to the south have developed in loess uplands. These yedoma deposits are extremely ice‐rich, and residual lakes found inside old lake basins (alases) are generally 2–4 m deep, reflecting continued talik development and ground subsidence following drainage of the original lake. However, where the expanding lake encroaches on the flanks of the upland at actively eroding bluffs, near‐shore pools develop that can be 6–9 m deep. It appears that thawing of ice‐rich permafrost during lake expansion causes ground subsidence and formation of deep pools above ablating ice wedges. These data suggest that thermokarst lake morphometry largely depends on the characteristics of the substrate beneath the lake and the availability of sediments eroded at the lake margin. Copyright © 2012 John Wiley & Sons, Ltd.