Magnitude and Duration of the Baltic Ice Lake Drainage Based on Modeling and Sediment Characteristics

Abstract:

At the time of the Pleistocene-Holocene transition, the Baltic Ice Lake catastrophically drained to the Atlantic Ocean over two narrow subaerial highlands (Mt. Billingen and Klyftamon) in south-central Sweden. The amount of water drained is known (7000 km³ resulting in a lowering of the water level 25 m), but the duration of the drainage and thus the magnitude of the discharge is not securely known. Here we present geomorphic and sedimentologic observations and modeling results that allow estimates of the peak velocity, peak discharge and overall drainage duration for the event. Newly available LiDAR based digital elevation models of the highlands has allowed identification of the boulder bars and fields formed during the drainage. D_­90 measurements on sediment in these deposits were used in velocity equations available in the literature, and they predict velocities ranging from 8 to 18 m/sec. Grain-size in these boulder deposits decreases downflow. The morphology of the boulder deposits varies with paleo-water depth. We also modeled the drainage duration assuming a simple ice-breach model. This model produced a peak velocity of 12 m/sec, agreeing well with the sediment data. This peak occurred about 5 months after the initial breach. The entire drainage took less than two years, although 75% of the drainage occurred within the first year.