Extreme cold during the penultimate ice age, the Saalien (238,000 to 116,000 years ago), caused a thick pack of land ice from the Arctic to come to this area. This brought with it many rocks that were crushed or deposited as boulder clay along the way. This produced undulations and moraines in the landscape. These traces of the ice age are still clearly visible around Steenwijk, at the Eese estate and on the high land near Vollenhove.