The Geological Society of America’s annual conference is being held in Minneapolis this week. In addition to many interesting lectures and presentations, the conference offers various field trips, including a full-day field trip that we attended: Flaming meteors, dark caves, and raging waters – Geological curiosities of western Wisconsin. What follows are a few notes and photos - Dianna Lord.
Crystal Cave, Spring Valley, Wisconsin
Blaze and Jean Cunningham provided a tour of their own personal cave (don't we all wish for our own personal geo sites!), The Crystal Cave, which they open to approximately 35,000 of the public each year. It is the longest cave (4,600 ft in length) in Wisconsin. The Crystal Cave tour teaches students about mineralogy, karst features, hydrology, speleotherms, soda straws, stalactites, stalagmites, flowstone, columns and various bat species that inhabit the caves..
Photo: A few of the sleeping bats in the Crystal Cave
Crystal Cave was formed in the lower Ordovincian Praire Du Chien Goup, which is a shallow marine deposit of dolostone and contains glaciofluvial deposits from the Wisconsin Glaciation period. In order to show the caves, in the 1900's the first owners removed much of the glacial deposits from the cave in order to allow people to tour the multi-level maize cave.
Photo: Flowstone and other cave formations in the Crystal Cave.
Eau Galle Dam
The Eau Galle Dam protects the town of Spring Valley and nearby areas from flooding, which happened on a regular basis until the dam was dedicated in 1968. It is the largest earthen dam in the Midwest. We walked across and viewed the beauty of the valley and surrounding areas, as well as the engineering involved in the building of the dam.
Photo: Group walking across Eau Galle Dam.
Gilman Iron Mine, west of Spring Valley
This privately owned land still displays the remnants of brown iron ore mining that was done in the late 1800s. At the peak of production, the mine provided 100-125 tons of pig iron per day.
We collected mostly limonite made of goethite an oxide mineral, which was formed in stratified blankets lying unconformably on Ordovician Prairie du Chien Group dolostones. The limonite lies beneath pre-Wisconsin drift and clay.
Photo: Dr. William S. Codua, professor of Geology at University of Wisconsin, River Falls explains the mining activities, geology and minerals at this mine site.
Rock Elm Disturbance, Pierce County, WI
Dr. William S. Codua, professor of Geology at University of Wisconsin, River Falls, led the group on a multi-stop tour of the Rock Elm Disturbance. It was a treat to learn how Dr. Cordua identified, research and published with his co-authors the finding of this impact crater. The finding of shocked quartz in the feature confirmed the other evidence, including a ring boundary fault, distinctive ring basin fill and the central uplift area.
The presentation illustrated an important principle in science: the investigation of anomolies. Why did crops grow poorly in certain areas? Why was the bedrock folded and brecciated in certain area and not others? Why is there no dolostone at certain elevations and instead shale interbedded with siltstone?
The shock features suggest an impact by an object about the length of 2 football fields. The evidence and case for the Rock Elm Disturbance is extensive and detailed, so please contact Dr. Codua for a copy of his papers written on this geological formation. It was both an informative and special field trip for all.
Photo: Siltstone discussion
