For 15 years, Cascade College in Portland, Ore., struggled to find the fuels that any college needs: students to pay tuition, and donors to help build an endowment.

Then came the global economic meltdown, and suddenly that struggle became an impossibility.

Late last month, the small Christian college with just 280 students and $4 million in debt announced it will have to shut down at the end of the current academic year.

"Our hearts would have said we would like to continue trying," said Cascade president Bill Goad. But on top of their long-term challenges, "small colleges like Cascade just don't have the slack to survive those kinds of impacts," he noted.

Colleges are remarkably resilient institutions. Princeton University's Nassau Hall still bears cannonball marks from a Revolutionary War battle nearby. Dickinson and Bowdoin colleges saw their first buildings burn down, as did the University of Vermont, which also survived its first president going insane.

Still, every year, a handful of institutions go under. And the current economic turmoil could accelerate the pace.

Another Christian institution, Taylor University, announced last month it will close the undergraduate program at a branch campus in Fort Wayne, Ind., and Pillsbury Baptist Bible College in Owatonna, Minn., announced plans to close.

Last week, Vennard College, a Christian school in Iowa that was down to about 80 students, announced it will close at the end of the current semester — two years shy of its 100th birthday.

If more college closing announcements come, it would likely be next semester, or next fall, when schools find out how many of their students don't return.

"We've seen what's happened to family income, the financial assets of so many families," said Matt Hamill, senior vice president of NACUBO, a college business officers' group. The key question is "how that will manifest itself when it comes time to enroll next fall."

There are about 4,400 colleges in the U.S., and the American Council on Education records that only four closed in 2007.

Mergers are somewhat more common, but outright closing rare for several reasons. Nonprofit colleges don't have to please Wall Street, and many have endowments they can tap. They also have an enviable business model: Students pay up front, often with large government subsidies. And families have proven willing to pay more and more for education each year, notes Roger Goodman, who analyzes college finances for Moody's Investors Service.

Still, even before the economic downturn, many small colleges were battling long-term challenges, from demographic changes away from the Midwest and Northeast, where many schools are located, to the perpetual difficulty of making the case that they are worth the extra cost over a state school.

Some colleges — like American consumers and homeowners — may discover they took on more debt than they should have, lured by low interest rates and ambitious growth plans. Private colleges' median debt has gone up 50 percent over the last five years, according to Moody's.

That didn't look like a problem, since revenue and donations have also been rising. But in recent months, like homeowners stuck in a variable-rate mortgage, some schools have seen their debt payments surge, thanks to the collapse of a complicated line of dominos that includes bond insurers and banks. Instead of holding long-term debt at lower interest rates, they have gotten stuck with short-term obligations at higher rates — a scenario they knew existed on paper but never expected to happen.

Others have become collateral damage from the collapse of Wall Street firms. Simmons College in Boston was placed on a watch list for a ratings downgrade because of an estimated $10 million exposure in a complex interest rate swap deal with now-bankrupt Lehman Brothers.