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Phoenix666 writes:

Phys.org:

The sightlines at Wrigley Field, the panorama from Navy Pier, the vantage points at the Adler Planetarium observatory—all structures built more than 100 years ago—are at least 4 inches lower now.

In the northern United States and Canada, areas that once were depressed under the tremendous weight of a massive ice sheet are springing back up while others are sinking. The Chicago area and parts of southern Lake Michigan, where glaciers disappeared 10,000 years ago, are sinking about 4 to 8 inches each century.

One or 2 millimeters a year might not seem like a lot, but "over a decade that's a centimeter. Over 50 years, now, you're talking several inches," said Daniel Roman, chief geodesist with the National Oceanic and Atmospheric Administration. "It's a slow process, but it's a persistent one."

While Chicago's dipping is gradual, this dynamic could eventually redefine flood plains and work against household sewer pipes that slope downward to the sewer main.

The subsidance could be after-effects of the disappearance of the ice sheet that once covered the area, or because the city is the location of the Hellmouth.

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