ABSTRACT

Anchor ice, i.e., ice attached to the bed in a lake, stream, or ocean, is common in the nearshore zone of southwestern Lake Michigan during winter. Lacustrine anchor ice has at least four distinct morphologies and was observed on sand, pebble, and boulder substrates in water depths to 4 m, the limit of diving traverses. The maximum depth of anchor ice formation may be much greater. Anchor ice is released from the lake bed on mornings following formation events. Released, floating anchor ice carries sediment to the water surface. This sediment is ice-rafted along shore and offshore under the influence of prevailing winds. We estimate that 0.85 m³ of sand per meter of beach is being removed from the nearshore zone of southwestern Lake Michigan by anchor ice annually. Melting ice drops this sand in deep water far from shore. This is a significant loss of sand from the sediment-starved nearshore zone of southwestern Lake Michigan.