The 2010 Flash Crash: A Trillion Dollars Gone in Minutes

On the afternoon of May 6, 2010, the U.S. stock market fell off a cliff and then climbed back up, all in about half an hour. For a few surreal minutes, roughly a trillion dollars of value vanished and reappeared, and no human had decided any of it.

What happened

Starting around 2:32 p.m. Eastern time, the Dow Jones Industrial Average plunged nearly 1,000 points, about 9%, in a matter of minutes, its largest intraday point drop up to that time. Then, almost as quickly, it rebounded. By 3:07 p.m. most of the loss had been erased. The whole violent round trip took roughly 36 minutes.

During the chaos, individual stocks behaved insanely. Shares of the consulting firm Accenture briefly traded for a single penny, while other stocks momentarily spiked toward $100,000. These were not typos; they were real trades that the exchanges later had to cancel.

Why it happened

The Flash Crash was not caused by bad economic news. It was a failure of market plumbing in an era when most trading is done by computers competing in fractions of a second.

• High-frequency trading dominates. Modern markets are run largely by algorithms that buy and sell in microseconds. Much of the market's apparent liquidity, the standing offers to buy and sell, comes from these machines.
• The liquidity vanished. When selling pressure spiked, many of these automated traders simply pulled their orders to protect themselves. With buyers suddenly gone, there was almost nothing to absorb the selling.
• Orders hit an empty market. With the normal buyers absent, sell orders crashed into a vacuum, driving prices to absurd levels like that one-cent print. Understanding this requires understanding the market maker role and the bid-ask spread, which both broke down.

The deeper point is that in 2010 there was no fundamental reason for stocks to be worth 9% less at 2:45 p.m. than they were at 2:30. Nothing had changed about the companies, the economy, or the news. The prices moved purely because of the order flow itself, a mechanical stampede rather than a change in what businesses were actually worth. That disconnect between price and value, compressed into minutes, is what made the event so unsettling to regulators and professionals alike.

The aftermath

Because the drop and recovery were so fast, most long-term investors barely noticed unless they had placed orders during the window. But those who had, especially anyone who used a stop-loss order, could be badly hurt: their stops triggered automatic sales at the crazy low prices before the rebound.

Regulators responded by strengthening and expanding circuit breakers, including new rules that briefly pause an individual stock if its price moves too far too fast. The goal is the same as after Black Monday: force a short timeout so the machines cannot cascade into oblivion.

The lesson

The Flash Crash revealed that a market can be deep and calm one second and utterly hollow the next, because the 'liquidity' provided by high-speed algorithms can disappear exactly when it is needed most. It also showed the hidden risk in automatic orders: a tool meant to protect you, like a stop-loss, can execute at a terrible price in a disorderly market.

To see how order types behave when markets go wild, compare a market order vs a limit order.