In the 2010 Flash Crash, about how many minutes did the steepest U.S. stock-market plunge last?

The steepest part of the 2010 Flash Crash lasted about 36 minutes.

On May 6, 2010, major U.S. stock indexes plunged rapidly in the afternoon before recovering much of the decline. The Dow Jones Industrial Average briefly lost nearly 1,000 points, an unusually large move for such a short period. Many individual securities also traded at extreme prices.

Investigations by U.S. regulators concluded that a large automated sell order in E-mini S&P 500 futures helped trigger a feedback loop involving high-frequency trading and rapidly falling liquidity. The event was not simply caused by one computer malfunction, however; market structure and automated responses amplified the move.

The crash led exchanges and regulators to introduce or strengthen safeguards, including single-stock circuit breakers and coordinated market-wide trading pauses. It showed how electronic markets could experience severe instability even without a conventional economic crisis.