DISTRIBUTION OF MAGNETIC SANDS ON LAKE MICHIGAN BEACHES NEAR MILWAUKEE WI

A study is underway to determine the causes of the variations in the amount of magnetic sand deposited at several beaches on the western shore of lake Michigan near Milwaukee, WI. We assume that the ultimate source is the erosion of the till bluffs that are prominent along most of the western shoreline. Results from a preliminary suite of samples collected at the same beach over a period of several years show differences that range from 1% to as high as 20% magnetite. This amount of variation could be due to changes in the lake level, shoreline morphology, or stream deposition

We are concentrating our initial quantitative study at a beach with both till bluffs and an ephemeral stream flowing to the beach. Samples are being collected at specific locations on a monthly basis as well as after storm events. Magnetic susceptibility of the sand fraction is being used as a proxy measure for the amount of magnetic material. Magnetic susceptibility is linearly related to the magnetic content and is quicker to measure than magnetic separation. Results from the first four months of measurements suggest that little magnetic material is entering from the stream, and that shoreline morphology may be dominating the present concentrations.