U.S. Geological Survey's upcoming geophysical survey of Decorah will mean low-flying aircraft

Low-flying helicopters and airplanes will be used by the U.S. Geological Survey in late December and in January to conduct a survey of rock formations around Decorah and Spring Grove.

The USGS says the area being surveyed is thought to be part of the 1.1 billion year old Midcontinent Rift, a major geological structure that contains significant deposits of nickel, copper and platinum.

To discover whether this is the case, a helicopter will carry large electromagnetic and regular magnetic instruments on a cable suspended from the helicopter. Also being used in the search will be a DC-3 retrofitted with modern avionics and gas turbine engines, which will garry "gravity gradient instruments."

Because different rock types differ in their content of water, magnetic minerals and density, the instruments will help scientists to determine what rocks are deep underneath the surface.

USGS officials say "None of the instruments carried on the aircraft pose a health risk to people or animals."

The aircraft will be operated by experienced pilots who are specially trained and approved for low-level flying. The helicopter and airplane will fly from 100 feet to 500 feet above the ground.

When the survey is completed the data collected will allow scientists to develop 3D subsurface maps that show mineral and water resources in the Decorah area.