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Friday the 13th, 2012, marks the 20th anniversary of one of the most unusual disasters in the history of Chicago, the Great Loop Flood of 1992.
A part of downtown Chicago is darkened Monday night, April 13, 1992 because of flooding in an underground tunnel that runs under Chicago's Loop. Thousands of workers were sent home early after the Chicago River water flooded subbasements.
(AP Photo/ ROB KOZLOFF)