Evolution of a high-mountain thermokarst lake in the Swiss Alps

Thermokarst lakes, a characteristic landscape element of the Arctic, are rarely found outside arctic situations. Here, a 30-yr photogrammetric monitoring series of a thermokarst lake in the Gruben area, Swiss Alps, is presented, The lake. situated in an environment of dead-ice remains and creeping permafrost, reached a final size of ca. 10,000 m(2) in area and 50,000 m(3) in volume before it had to be drained artificially in 1995. Starting in the mid-1960s it grew with radial rates of ca. 1.5 to 5 m yr(-1). Nonlinear coupling of lake diameter and energy turnover led to accelerated area growth. The development of the lake was presumably driven by thermal convection of water. By a dynamic model of lake growth, we show that a change in climate conditions and/or the lake bottom topography could have,significantly influenced the observed lake growth. The effective energy turnover used for ice-melt and subsequent lake growth was estimated to be in the order 10(0) to 10(1) W m(-2).