1 3 2 , 0 0 0 ▁years ▁ago , ▁blocked ▁the ▁Mississippi ▁near ▁Rock ▁Island , ▁diver ting ▁it ▁into ▁its ▁present ▁channel . ▁After ▁the ▁gla cier ▁m elt ed , ▁the ▁Illinois ▁River ▁flow ed ▁into ▁the ▁ancient ▁channel . ▁The ▁Hen ne pin ▁Canal ▁roughly ▁follows ▁the ▁ancient ▁channel ▁of ▁the ▁Mississippi ▁up stream ▁of ▁Rock ▁Island . ▁ ▁The ▁modern ▁channel ▁of ▁the ▁Illinois ▁River ▁was ▁sh aped ▁in ▁a ▁matter ▁of ▁days ▁by ▁the ▁K ank ake e ▁Tor rent . ▁During ▁the ▁mel ting ▁of ▁the ▁Wisconsin ▁Gla cier ▁about ▁ 1 0 , 0 0 0 ▁years ▁ago , ▁a ▁lake ▁formed ▁in ▁present - day ▁Indiana , ▁compar able ▁to ▁one ▁of ▁the ▁modern ▁Great ▁L akes . ▁The ▁lake ▁formed ▁behind ▁the ▁terminal ▁m ora ine ▁of ▁a ▁subst age ▁of ▁that ▁gla cier . ▁Mel ting ▁ice ▁to ▁the ▁north ▁eventually ▁raised ▁the ▁level ▁of ▁the ▁lake ▁so ▁that ▁it ▁overflow ed ▁the ▁m ora ine . ▁The ▁dam ▁burst , ▁and ▁the ▁entire ▁volume ▁of ▁the ▁lake ▁was ▁released ▁in ▁a ▁very ▁short ▁time , ▁perhaps ▁a ▁few ▁days . ▁ ▁Because ▁of ▁the ▁manner ▁of ▁its ▁formation , ▁the ▁Illinois ▁River ▁runs ▁through ▁a ▁deep ▁can y on ▁with ▁many ▁rock ▁form ations . ▁It ▁has ▁an ▁" under util ized ▁channel ", ▁one ▁far ▁larger ▁than ▁would ▁be ▁needed ▁to ▁contain ▁any ▁conce iv able ▁flow ▁in ▁modern ▁times . ▁ ▁History ▁ ▁The ▁Illinois ▁River ▁valley ▁has ▁long