The Kankakee Torrent and other large meltwater flooding events during the last deglaciation, Illinois, USA

• The Kankakee Torrent, a large meltwater flood, occurred ∼19,000 cal yr BP.
• The Kankakee Torrent occurred in the south-central sector of the Laurentide Ice Sheet.
• The Kankakee Torrent filled three moraine-dammed basins, forming proglacial lakes that covered about 6.22 × 109 m2.
• Their drainage supplied about 10.2 × 1010 m3 of water to the Gulf of Mexico.
• GIS analysis of an isostatically warped DEM provided verification of overflow paths and relative age of overflow channels.

Evidence of the Kankakee Torrent (Ekblaw and Athy, 1925) includes boulder bars formed on a scoured bedrock surface west of Kankakee, Illinois, and overflow channels that connect several moraine-dammed basins (Wauponsee, Watseka, and Pontiac; Willman and Payne, 1942). Geomorphic evidence of a large scale flood event in the Illinois Valley includes features such as erosional residuals (Hajic, 1990). The age of the Kankakee Torrent is about 19,000 cal yr BP based on the pooled mean of four radiocarbon ages of tundra plant stems and leaves from the Oswego channel complex (median probability = 18,930 cal yr BP, σ1 range, 18,870–18,970 cal yr BP). Analysis of recently obtained sediment cores from the middle Illinois River valley near Havana, Illinois, has revealed the bedrock surface is defended by a mantle of bouldery debris buried by 15 m of mostly slackwater lake sediment. Radiocarbon ages of needles archived in the lake sediment reveal evidence for an early lake phase that post-dates the Kankakee Torrent (18,030–17,530 cal yr BP) and a later lake phase (15,690–13,040 cal yr BP). The radiocarbon ages indicate that the deeply buried bouldery rubble was deposited by the Kankakee Torrent. Consideration of isostasy indicates that the earlier lake phase at Havana may have been associated with downward flexure of land surface in response to glacier loading. The younger lake phase was caused in part by deposition of a sediment dam (the Savanna–Deer Plain terrace) at the mouth of the Illinois River. The lake shoaled due to passing of the isostatic forebulge across the area.