Beware the 'melt-up:' Analysts say stocks may soar just before they collapse

Storm clouds appear to be gathering over Wall Street, with many analysts saying a downturn is inevitable. But before the party winds down, some expect an explosive pre-crash rally — known as a "melt-up."

Melt-ups usually occur without any obvious economic reason for the gains. They happen when investors buy assets based on greed, or fear of missing out, instead of fundamental improvements.

First, some quick context: The past five years have been very, very good for investors. The S&P 500 has grown by nearly 90%, and the tech-heavy Nasdaq has grown over 140%. That includes two years of a pandemic that shuttered businesses and snarled global supply chains.