The 2010 Flash Crash Explained

The Flash Crash of May 6, 2010

On May 6, 2010, the U.S. stock market experienced its most volatile intraday period in history. The Dow Jones Industrial Average plunged about 998 points (roughly 9%) in just minutes, before recovering most of the loss within 20 minutes.

Timeline of Events

• 2:32 PM: A large sell order of E-mini S&P 500 futures (75,000 contracts, ~$4.1 billion) was executed by an automated algorithm
• 2:41 PM: The selling pressure cascaded through the market
• 2:45 PM: The Dow hit its intraday low, down ~998 points
• 2:47 PM: Circuit breakers triggered, buying programs kicked in
• 3:00 PM: The market had recovered most of the loss

What Caused It?

The Trigger

Waddell & Reed, a mutual fund firm, used an automated execution algorithm to sell $4.1 billion worth of E-mini futures. The algorithm was programmed to sell at a rate of 9% of the previous minute's volume — without any price limit.

The Amplification

1. High-frequency traders (HFTs) initially absorbed the selling but quickly stopped providing liquidity
2. Stop-loss orders were triggered en masse, creating a cascade
3. Cross-market contagion — futures market selling spread to individual stocks
4. Some stocks traded at absurd prices — Accenture hit $0.01, Apple hit $100,000

Lessons for Algo Traders

1. Always use price limits in execution algorithms
2. Liquidity can vanish instantly during stress events
3. Market microstructure matters — understand how your orders interact with the market
4. Circuit breakers are now in place but can't prevent all flash crashes
5. Test stress scenarios — what happens to your strategy during extreme volatility?

Regulatory Response

• SEC implemented single-stock circuit breakers (now called LULD — Limit Up-Limit Down)
• Consolidated audit trail was mandated for better surveillance
• Market makers were required to maintain quotes during volatile periods

This content is for educational purposes only and does not constitute investment advice.