How is tourism industry affected due to economic crisis?

Most travel and tourism involves discretionary (extra cash lying around to spend on anything) expenses and if people have less of it, then the tourism industry will be affected. People want to conserve their cash so they can pay for the necessities (food, shelter etc). Their holiday/travel plans can change. They could spend less when going on holidays, travel closer to home or just not travel at all. This can be during an economic crisis or even when something happens in another part of the world like when the Icelandic volcano erupted in 2010 which disrupted flights and holiday plans for thousands of people.