An evaluation of ice-rafted erosion caused by an icefoot complex, southwestern Lake Michigan, USA

The Lake Michigan icefoot complex at Wilmette, Illinois, USA, has a variable and transient nature. Data collected during winter 1988/89 show an alternation of additions to and subtractions from the volume of the complex. A total of 548 m³ of ice per linear meter of shoreline (m³ m^-1) were added to the complex in discrete masses throughout the winter. All additions of ice were sampled to determine the weight of enclosed sediment. The total weight of sediment added to the complex by wave action during ice formation was 4.1 Mg per m of shoreline (Mg m^-1). Eolian action and basal freeze-on also subsequently contributed sediment to the icefoot complex. These amounts were respectively calculated to be 1.5 and 0.3 Mg m ^-1. Wave impacts are the primary mechanism of icefoot complex destruction and subsequent dispersal of ice blocks into the nearshore zone. Time-lapse filming of the beach shows this destruction, with ice pieces being transported by southerly longshore currents. An estimate of enclosed sediment set adrift from the site in this manner totals 5.4 Mg m^-1. It is hypothesized that ice-rafting caused by the breakup of an icefoot complex is capable of transporting sediment to a depocenter in southern Lake Michigan. -Authors