WTTW News Explains
WTTW News Explains: Why is Chicago Sinking?
Attention Chicagoans, brace yourselves because Chicago is sinking.
Yes, you heard right, sinking!
The more sciencey-name is land subsidence. But whatever you call it, the city is descending by more than 2 millimeters each year. That’s about 1/16 of an inch.
To get to the bottom of the matter, you need to rewind 20,000 years, when a glacier covered the entire city. The weight of that ice caused downward motion, and when it was gone, a rebound deformed the Earth’s crust as well as helping create our clay-based soil.
Fast forward to today. We all know about climate change. But Northwestern University researchers were the first to study underground climate change and its effects on urban infrastructure. They call it a “silent hazard.”
They installed temperature sensors around the city, including below ground. Turns out, the layers of clay under Chicago are deforming over time due to the rising underground) temperatures.
In fact, Northwestern says the underground temps in parts of Chicago have risen 27 degrees since the 1950s.
The culprit: buildings, transportation systems, and other infrastructure creating heat that stays underground.
Open space allows the ground to “breathe” a bit, so the hottest temps are under streets, sidewalks and buildings.
A study of 28 cities revealed at least 20% of the land in every one of them is sinking, and most have 65% or more subsiding.
Those researchers cite groundwater extraction and expanded urban development as additional contributing factors and warn that “even slight downward shifts in land can significantly compromise the structural integrity of buildings, roads, bridges, and railways over time.”
So, what’s to be done? Scientists recommend increasing energy efficiency and reusing so-called “heat waste” on the surface before it travels underground, for a start.
It looks like action today may save future generations of Chicagoans from living in a hole in the ground. Or at least from having their buildings fall down.
