(CBS) If a dam north of Mosul, Iraq, collapses it could send a trillion-gallon wave of water roaring through Iraq's two largest cities - and the U.S. Army Corps of Engineers has warned that is perilously close to happening, CBS News correspondent Allen Pizzey reports.

The dam is on the Tigris River, 45 miles north of the city of Mosul.

A catastrophic failure, engineers believe, could unleash a 60-foot-high wall of water that would be inundate Mosul - and flood Baghdad to a depth of 15 feet.

The casualty count would be in the hundreds of thousands.

The United States has supplied $27 million worth of equipment to upgrade this aging machinery used for reinforcing, which has been a problem since the dam was built in 1984.

Nevertheless, a report to be released today says that because of potential erosion, the Mosul Dam is “the most dangerous dam in the world.”

The problem is that it was built on a type of rock that dissolves when it comes into contact with water.

In a telephone interview, the Iraqi minister of water resources admitted there were, in his words "some problems," but added that his ministry was "planning to design a permanent solution."

In spite of the Iraqi government's professed confidence, Ambassador Ryan Crocker and Gen. David Petraeus sent a letter to the Iraqi prime minister in May stating that the damn presented “unacceptable risks.”

Given that a break could trigger a flood of Biblical proportion, that may go down as a classic example of diplomatic understatement.

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