Explanation:
Glaciers can be thought of as rivers of ice, slowly flowing outward from their source to their terminus. Rates of ice flow range widely, but it is thought that the glaciers that affected Indiana probably moved relatively rapidly because they had abundant water at their bases to help "lubricate" their sliding motion over their beds. This sliding motion allows a vast amount of older rock and sediment to be eroded from the bed of the glacier, where it becomes frozen into the lower part of the ice. Thus, glaciers could be viewed in one sense as "conveyor belts", constantly transporting sediment from back up under the ice to the glacier margin. The edge of a glacier is where the ice is always melting. When melting rates are slow (for example, during winter or other especially cold times) and accumulation of new ice is rapid, the ice margin moves outward, or advances, whereas when melting rates are high, the opposite is true. In any event, the constant melting that goes on at the margin of a glacier releases vast amounts of entrained sediment, some of which may have traveled as frozen debris in the glacier for hundreds or even thousands of miles from its source. At the scale of the continental ice sheets, the quantity of sediment transported must have been astonishing. In Indiana alone, countless tens of feet of soil and bedrock were stripped off the landscape and redeposited down-glacier, along with even larger quantities derived from areas farther north. Hence, it is not surprising that the deposits of Ice Age glaciers are the dominant material in the Indiana landscape today, ranging up to several hundred feet thick in some places in the north.
But a landscape need not be directly affected by ice to be dramatically changed. As noted above, conditions just outside of a continental ice sheet are severe. Precipitation of potentially monsoonal proportions, coupled with a far greater frequency and intensity of freezing and thawing can set entire landscapes in motion. Recently thawed, super-saturated sediments on even a gentle slope will move easily under their own weight, creating widespread mud flows and extreme instability of the landscape. This process, called "solifluction", was probably very widespread within a zone of tens to perhaps a hundred miles wide fringing every ice sheet that invaded Indiana. The most extreme example of this landscape is permafrost, where a thick layer of permanently frozen ground exists at a shallow depth beneath a thin upper layer that experiences annual freeze and thaw action. The boundary between the frozen substrate and the soupy surface material is exceptionally unstable and results in constant rearranging of the landscape. There is good evidence that localized permafrost existed in a few places in northern Indiana during the waning stages of the Wisconsin ice sheet, and it seems quite possible that permafrost may have been more widespread during parts of the Illinoian glaciation, when the coldest global temperatures of the Ice Age were recorded in sea floor sediments and the ice sheets in Indiana extended to the Ohio River
