March 4th luncheon registration may now be completed online.  Please register online by Thursday, February 27th.  You will no longer have to email our Communications Director, Mary Sitko, to register for future luncheons unless your registration needs cannot be addressed online.

Advance luncheon registration cost is $21 for non-members and $16 for members.  Students may attend free of charge.  Same-day luncheon registration cost is $25. 

The March 4th Luncheon will be sponsored by Nova Consulting Group Drilling

Presentation Title

The Discovery of French Saltpeter Caves in Minnesota by Greg Brick, PhD

Presentation Abstract

Prompted by French fur-trader Pierre-Charles Le Sueur's 1700 report of caves containing saltpeter (potassium nitrate) along the Minnesota shore of Lake Pepin, this study located what are thought to be the original caves and revealed a hitherto unsuspected widespread district of cave nitrate deposits in the Upper Mississippi Valley (UMV). Of the 103 caves sampled from nine geologic formations, 67% had elevated nitrate concentrations (>50 ppm NO₃) in their sediments relative to surrounding surface soils (3). These nitrate concentrations, up to 3.5 percent dry weight of sediment (35,000 ppm), are comparable to the concentrations found at Mammoth and Dixon caves, Kentucky, an historical nineteenth-century saltpeter mining locality, which range from 0.01 to 4 percent. But the Hill (1981) seeping groundwater model, which satisfactorily accounts for the nitrate deposits of the historic saltpeter caves of the southeastern United States, does not apply in the UMV. Through the application of geochemical and isotopic analysis to soil solutions it was concluded that the source of the nitrate was organic matter such as guano, scats, urine, carcasses, and plant materials, and that the nitrate accumulated because the cave roof protected the soluble nitrate ion from leaching and by blocking out sunlight, prevented plants from growing and thus extracting this nutrient. Le Sueur's claim of finding saltpeter (more likely, a saltpeter precursor, such as calcium nitrate) in Minnesota caves, for making gunpowder in the wilderness, is thus credible.

Presentation Abstract

Greg Brick Ph.D. was employed as a hydrogeologist at several environmental consulting firms and taught geology at Normandale Community College, the University of Wisconsin-River Falls, and the University of St. Thomas. He has edited the Journal of Spelean History for the past decade and in 2005 was the recipient of the National Speleological Society’s Cave History award. His first book, Iowa Underground: A Guide to the State’s Subterranean Treasures, was published in 2004. His latest book, Subterranean Twin Cities, published by the University of Minnesota Press in 2009, won an award from the local chapter of the American Institute of Architects. His doctoral research on saltpeter caves is the subject of today’s presentation.