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Mine Shafts Causing IA Sinkhole

DUBUQUE, IA (CBS2/FOX28)  When a sink hole swallowed a man and his entire house in Florida one year ago, the phenomena went from being a scientific curiosity to a deadly menace. Thats why when his neighbors driveway dropped six inches in one night in Nick Thummas Dubuque neighborhood, he immediately became concerned.

The street in front of the home he just moved into in March disappeared three times before. As of Monday night a cavernous pit about 20 feet deep and 50 feet across had opened once again.  It snapped the water main to his house and made Thumma wonder if it might keep growing, If theres a shaft here in the street, does that mean theres one that runs under my home or into my yard .. so thats a concern.   

Here along the Mississippi River in Dubuque that sinking feeling is less about geology and much more about history.  The city is built on top of a maze of old mine shafts.  Lead and zinc mining, starting in the late 1700s, created boom towns from Platteville to Galena to the bluffs of Dubuque.

Thumma says that may be common knowledge for some, but he would like to see the city warn people that they all could be at risk for similar problems.  By some accounts there are more than 90 miles of horizontal mine shafts running under the city and another 2,000 vertical.

Assistant City Engineer Bob Schiesl says unfortunately early miners were not good map makers and when they finished with a vein they normally walked away with no thought of filling in the void. Schiesl says there are miles of shafts that were never recorded at all and most of the records from the 1800s are less than accurate.

He says the standard repair is to fill the holes with large rock, then fill the rest with concrete until it reaches street level. He says, so far, they just havent found the bottom of this one and crews will try again Tuesday to fix it and reopen Ramona Street.
Thumma says in addition to raising awareness hes talking to lawmakers about insurance.  He says you can buy flood and fire insurance in Iowa, but nothing to guard against damage from sink holes.  Living around so many potential pit falls in Dubuque, he says he would like to at least see that much change.

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