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The Point: The Underground River


  • The proper name of our "Underground River" is the "Wisconsin Glacial Flow." Its size varies from one-half to one mile wide and its depth from 15 to 35 feet. It is not a river in the same sense that the Allegheny or Ohio are rivers. It might be compared to an oval tunnel, completely filled with rocks and gravel. The sides and bottom are solid rock and the top is silt and clay. This clay top that separates it (where necessary) from the Allegheny and Ohio varies from several feet to as little as three feet thick in some places. (8)

  • In the beginning the waters of the Ohio and Allegheny rivers flowed northward to the St. Lawrence River. During the ice age, glaciers pushed southward toward our area, and the great river valleys were filled with rock and gravel. The bottom of our "Underground River" had been formed (carved) milleniums ago by the northward flowing rivers.

    The northward flow of the rivers was blocked by glaciers and new outlets southward were created. Clay and silt were deposited over the layers of gravel, sealing them off from the surface rivers formed "shortly" thereafter. Through the deposit of gravel and rock our "Underground River" flows at the slow rate of five or six miles a day. (9)

  • So far as geologists have been able to determine, the first to tap this hidden resource was the Harmony Society, which drilled a well in Ambridge area in 1873. Whether they realized the significance of this well is uncertain. But by this time they were hiring geologists to locate oil wells on their lands in Northern Pennsylvania, and one of these may have reasoned that pure water could be found by tapping the glacial drift of the Allegheny-Ohio valley. (10)

  • Pittsburgh's "underground river" is what geologists call an "aquifer," but it differs from other aquifers in that most of them are irregular and widespread and do not follow a channel. This makes our underground river more nearly like a true river than other aquifers. (11)

  • By far the most visible evidence of Pittsburgh's fourth river is the great Point Park Fountain, which uses water pumped to the surface by specially designed pumps housed in two small buildings at left and right of the fountain. (12)


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