Lake Michigan sand deposits from Kenosha, Wisconsin, to Chicago are being mapped over the next week with innovative technology never before deployed for mapping the bottom of the Great Lakes.
This the initial critical data-gathering project of a team of scientists who have set a goal to better understand and preserve the ever-changing 63-mile Illinois coast. This work is a collaboration between the Illinois State Geological Survey (ISGS) and the Illinois Department of Natural Resources’ Coastal Management Program (CMP).
The goal is to improve the scientific understanding of how the coast changes in response to storms, fluctuating lake levels, and nearshore ice. “We know the lake level fluctuates, but the amount of change from year to year or decade to decade is not constant, which exerts a variable and unknown impact on beach and nearshore sand deposits,” said Ethan Theuerkauf, a coastal geologist at the ISGS who is studying how physical forces drive coastal change along Lake Michigan. The precision snapshot of sand deposits along our Lake Michigan coast gathered during this study will form the foundation for future scientific studies of the geology and ecology of our coast.
A helicopter is carrying a six-sided mapping instrument (antenna) along the WI-IL Lake Michigan shoreline; this instrument can gather information about beach and underwater lake-bottom layers at some 150 miles an hour. The mapping corridor extends about 2,300 feet from the shoreline into the lake. The deepest water is likely to be no more than 100 feet.
The data consists of measurement of differences in how an electro-magnetic field projected down through lake water and into the geologic layers of the lake bottom is ”read” by a receiver under the helicopter. Different geologic layers under the lake bottom have different physical properties, and those are measured as telltale differences in how they conduct and resist electricity.
This is a fairly new and powerful mapping technique called helicopter time-domain electromagnetic mapping. “This technique is a game changer on how we acquire subsurface information whether it is under the water or deep underground,” said Richard Berg, ISGS director and Illinois State Geologist. The result will be a detailed three-dimensional computer model of what is under the surface.
“Flying a helicopter seems expensive, but compared to boat-based mapping, drilling or lake-bottom sediment sampling, it is time- and cost-efficient because we can cover the whole Illinois shoreline in just a few days,” said Kisa Mwakanyamale, ISGS geophysicist and project principal investigator. “It’s quick and more comprehensive than any other technique that currently exists.”