What Happens to the Economy When a Lot of Loans Are Defaulted on?

loans

I’m trying to work this around in my head, but no luck so far. How exactly does this work? When you take a loan out and repay it back, the economy gains more money, but what happens when a lot of people default on their loans? Like…for student loans or a touch? Would it cause a touch like the subprime mortgage crisis to happen?

How Does Greece Debt Obstruct Economic Recovery Worldwide?

debt

The media does poor job in amplification how Greek debt has huge potential to hurt US economy. If Greece is bankrupt and does not pay its bills, then how is that related to economic movement of the world? Its not clear. In the likely event that Greece will continue to default and be incorrect on everything, how is US economy unnatural? And why the riots?