Decorah Ice Cave State Preserve

Decorah Ice Cave is recognized as one of the largest known “glacières” (caverns containing ice) in the Midwest. This 3-acre preserve is located on the southern edge of the Barbara Barnhart VanPeenen Memorial Park, in the northern part of the city of Decorah. It is known for the unusual deposits of ice that coat its walls and floor, usually well into summer. The bluff that includes the cave was acquired in 1954 by the Decorah City Parks Commission and with a gift from Jennie Edmunds Moss in memory of her brother, Roger F. Edmunds. The tract including the cave was dedicated as a geological state preserve in 1973. The cave is owned and managed by the city of Decorah. The entrance to the cave is up a steep flight of stairs located just east of the parking area. A narrow passage extends into the massive limestone bluff for 120 feet. For the first 10 feet inside the cave, the floor rises slightly and is usually free of ice. For the next 30 feet, the floor slopes gradually, and ice is consistently present along the floor and walls during spring and summer, especially the north wall. Caution is advised, as footing can be hazardous in the cold, dark, slippery environment. Also, rocks may be loose and should not be disturbed. The cave passage follows a prominent vertical fracture extending through the limestone, and this thin parting has been enlarged by the gradual slippage of massive rock blocks downslope—a geologic process referred to as “mechanical karst.” The shape of the cave results from the outward rotation of limestone on the under­lying softer, groundwater-lubricated Decorah Shale. The cave itself is formed in the Galena Group, a 450-millionyear-old limestone and dolomite (magnesium-rich limestone) of Ordovician age. Ice formation is caused as cold winter air sinks into the cave chamber, bringing the surrounding rock walls to temperatures well below freezing. Ice buildup occurs with the spring thaw when surface water seeps into the cave and is frozen by contact with the cold rock walls and the trapped cold air. Ice begins to form in March and usually reaches its maximum thickness of eight to ten inches in early June. Gradually the temperature rises throughout the spring and summer, so that by the middle of summer, the ice-chamber temperature rises above freezing and the accumulated ice begins to melt. By the time cold weather returns in autumn, the cave is usually free of ice and remains relatively dry throughout the winter. These conditions can vary from year to year, depending on seasonal weather patterns. The cave has an interesting history of scientific investigation and also was commercially shown from 1929 until 1941 at a cost of 10 cents, or 25 cents for a guided tour. Today the cave is open to the public free of charge. Other state preserves in the vicinity include Cold Water Spring, Malanaphy Springs, and Bluffton Fir Stand.