The cost of a US university degree has left people wide-eyed for decades but student debt has now mushroomed into a nightmare for Americans with potential to explode as the next major US financial crisis.

Students at the University of Notre Dame in Indiana, for instance, can typically expect to borrow $23,445 to top off the total $31,812 they might need. And that's just for the first (or freshman) year of a four-year degree.

"You'll pay approximately $1,414 per month for 10 years to cover your total borrowing" once schooling is completed, the Consumer Financial Protection Bureau, a federal agency, says on its website

"This equals 29 $50 textbooks every month."

It's relatively easier at Harvard (typical first-year borrowing stands at $16,459, because average grants and scholarships are higher) and the University of California in Los Angeles ($13,796 in borrowing), but the picture is clear.

Two years ago, for the first time, total outstanding student debt in the United States topped $1 trillion, according to the National Association of Consumer Bankruptcy Attorneys.

That's more than what Americans owe on their credit cards.

"Take it from those of us on the front line of economic distress in America: this could very well be the next debt bomb for the US economy," said the organization's president William Brewer.

"The reason: Students and workers seeking retraining are borrowing extraordinary amounts of money through federal and private loan programs to help cover the rising cost of college and training," he added.

"In many cases, parents responsible for the student loans are in or near retirement years and facing repayment demands."

On average, a bachelor's student who graduated in 2010 did so with $25,250 of debt. But more and more, parents are borrowing to help their children get a degree -- and finding themselves typically owing $34,000 in the process.

While tuition fees keep going up, the duration of borrowing grows longer. According to the Federal Reserve Bank of New York, a third of all student debt is owed by adults over the age of 40, and 4.2 percent is owed by over-60s.

Typical of those in the prime of life who are still paying off student loans is Donna Shelton, 51, who finished her bachelor's degree in her early 20s, then resumed medical school at the age of 39.

"I took out $121,000 in student loans to cover undergraduate and graduate school," she told AFP. "I hope I live past my 80s -- but if not, I will die with outstanding student loan debt."

Shelton budgets $750 a month to pay back student loans. That's not bad compared to her partner, a teacher who forks over half of his monthly paycheck.

Among all those who borrowed for education in 2005, one in four had problems making payments, and 15 percent could not pay back anything at all.

Washington waiter Colin Pinkham, 27, decided a year and a half ago to stop paying back the more than $75,000 he still owes for his degree in East Asian history that he earned in 2003.

"I was put in a situation where either I could afford to pay my rent, and pay for food, or I could pay my student loans," he said via Occupy Student Debt, which campaigns for student debt relief.

John Rao, vice president of the National Association of Consumer Bankruptcy Attorneys, noted in a statement how student debt can have knock-on effects -- delaying, for instance, decisions on marriage and starting a family.

And the spiral can be eternal, notably for those unable to find work or who ran up debt to train for a career that fails to pay well.

From 1980 through 2010, tuition fees in the United States have doubled on average, reaching several tens of thousands of dollars at some public as well as private institutions, according to the Institute of Education Sciences.

One third of students pay their tuition in full, without grants or scholarships, the College Board said.

Protests over student debt have targeted the Washington offices of Sallie Mae, the biggest private lender, while on, some 670,000 people have signed onto a petition urging the US government to forgive student debt "as a means of economic stimulus."

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