SANDSTONE CANYON EROSION AT STARVED ROCK STATE PARK, ILLINOIS

Starved Rock State Park in northern Illinois is characterized by fascinating box canyons along the Illinois River. It is generally accepted that box canyons are formed by seepage erosion in the arid western U.S., but in the humid midwestern U.S. the importance of seepage erosion as a primary shaping factor is often overlooked and the box shape is often attributed to erosion by flowing water. Field observations indicate that ice and flooding may be the two most powerful erosive forces at work on the canyons. These observations suggest that seepage erosion may be the dominant erosional force in the late winter; as the ice begins to melt it breaks free from the rock face and removes a significant amount of sediment. Observations also suggest that erosion from flowing water may be the dominant erosional force in the months prone to rainfall; as influxes of water fill the canyon floor loose sediment is washed away. Field observations as well as panoramic photo surveys of the canyon heads indicate that the height of seepage-related erosion alcoves that frequent the canyon walls fall within several meters of each other, this may indicate an area more susceptible to seepage erosion in the rock. Further work will include remote sensing analysis of Quickbird imagery of the Starved Rock State Park area.