The market is setting up for a big decline that could be as bad as the crash of 1987, according to Marc Faber, known as "Dr. Doom." He just isn't sure exactly what will set it off.
"The problem with crashes, you never know beforehand precisely what is the catalyst," the publisher of the Gloom, Boom & Doom report told CNBC's "Closing Bell."
It could come from the credit market, equities being perceived as too expensive or a geopolitical event, he added.
"I think it's a colossal bubble in all asset prices, and eventually it will burst, and maybe it has begun to burst already," Faber said.
He's calling for a 30 percent decline in the S&P 500.
