The 2010 Flash Crash — an Instant Plunge Made by Algorithms
Would you believe that 1 trillion dollars vanished from the market within minutes, then most of it came back within tens of minutes? It actually happened in 2010.
What Happened
On the afternoon of May 6, 2010, the Dow Jones Industrial Average plunged about 1,000 points (about -9% at the time) within minutes. In less than 30 minutes, about 1 trillion USD in market capitalization vanished.
But the index almost immediately reversed most of it, recovering a substantial portion within about an hour. It was an unprecedented event in which a plunge and rebound occurred in an instant, with no clear bad-news catalyst.
The Cause — Algorithms and High-Frequency Trading
Initially a single trader's "fat finger (a typo-driven massive order)" was blamed, but later investigation concluded that an algorithm processing one large sell order was the trigger, and high-frequency trading (HFT) programs buying and selling among themselves amplified the volatility.
With programs, not people, reacting on a millisecond scale, liquidity dried up in an instant.
After this event, exchanges canceled abnormal executions and strengthened circuit breakers and volatility-mitigation mechanisms that briefly halt trading when an individual stock moves sharply.
The Lesson for Investors
The flash crash dramatically shows that "prices do not always move rationally." In particular, market orders and stop-loss orders can be executed at the worst prices in such moments.
The implication for long-term investors is simple. Rather than reacting to a few-minute swing by buying and selling, it is safer to maintain from the start a bearable weight and spare funds so you are not forced to sell during a sharp swing.
Frequently Asked Questions
Q. What happens if I have a stop-loss order during such an instant plunge?
If the price drops below your specified level in an instant, the stop-loss order can be executed at a far lower price than expected. During the flash crash, some stocks were executed at extremely low prices and the trades were later canceled. Understanding the characteristics of order types is important.
Q. Could a flash crash happen again?
The rules have been supplemented, but similar instant swings have been observed several times since. As long as algorithmic trading makes up a large share of the market, it is hard to eliminate entirely. Rather than predicting, the preparation is to build an investment structure that is not swayed by short swings.
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