Black Monday — October 19, 1987
The largest single-day percentage crash in Wall Street history: -22.6% in just a few hours
On October 19, 1987, the Dow Jones lost 22.6% in a single trading session — still the worst daily percentage drop in history. A fundamental case study on how automated mechanisms can amplify market crashes.
The Pre-Crash Context
Global stock markets had experienced an extraordinary bull run in the first half of the 1980s. The Dow Jones rose from 776 points in 1982 to 2,722 points in August 1987 — a 250% gain in five years.
In the weeks leading up to the crash, several tensions had accumulated:
- Rising interest rates (US Treasuries at 10%)
- Weakening dollar
- Widening US trade deficit
- Geopolitical tensions with Iran (Tanker War)
Monday, October 19, 1987: The Day of Disaster
The opening bell signaled a sharp decline, following a negative week. However, what followed went beyond all predictions:
9:30 AM: NY open with heavy selling 10:00 AM: Market accelerates to the downside 11:00 AM: Sell orders multiply 2:00 PM: Total panic Close: Dow Jones -22.6% — 508 points in a single day
The stock value wiped out was $500 billion — a quarter of the US GDP at the time.
The Role of 'Portfolio Insurance' and Program Trading
The decisive technical factor was portfolio insurance — an automated hedging strategy widely used by institutional funds. It worked like this:
- As prices fell, computers automatically sold S&P 500 futures
- These sales drove futures prices down further
- Low futures prices triggered other traders to sell the underlying stocks
- Stocks fell, triggering new automatic sales
A negative feedback loop between cash and futures markets. The Chicago Mercantile Exchange — where S&P futures were traded — was literally flooded with sell orders that could not find buyers.
The Fed's Response: Alan Greenspan
The new Federal Reserve Chairman, Alan Greenspan, had been appointed just two months earlier. On the morning of October 20, he released a brief statement that became historic:
'The Federal Reserve, consistent with its responsibilities as the Nation's central bank, affirmed today its readiness to serve as a source of liquidity to support the economic and financial system.'
This guarantee was sufficient: markets rebounded by 5.9% as early as October 20. The Fed had introduced the so-called 'Greenspan Put' — the implicit promise that it would always provide liquidity in the event of a crisis.
Consequences and Reforms
Circuit Breakers: After Black Monday, stock exchanges introduced automatic trading halts in the event of rapid crashes — still in use today.
International Coordination: The crash was global (Tokyo -15%, London -26% in the following weeks), highlighting the need for coordination between global exchanges.
Historical Irony: The expected recession never arrived. The US economy continued to grow, and Wall Street fully recovered in less than two years.
The Fundamental Lesson
Black Monday was the first large-scale demonstration of how automated mechanisms can amplify market movements beyond any fundamental rationality. With the expansion of trading algorithms, this risk has increased — not decreased.