The 2016 Sterling Flash Crash
In thin overnight trading in October 2016, the British pound dropped roughly 6% against the dollar in under two minutes and mostly recovered soon after, with algorithmic trading amplifying an already illiquid moment.
In the early hours of October 7, 2016 — during the thinnest window of the trading day, when Asian markets were open but London and New York were not — sterling fell about 6% against the dollar in a matter of minutes, touching its weakest level in over three decades, before recovering most of the move within the hour. No single piece of news explained a drop of that size that fast.
A subsequent BIS review found the crash wasn't caused by one shock but by a cascade — thin overnight liquidity meant a moderate wave of sell orders pushed prices through levels that triggered stop-losses and algorithmic hedging, which triggered more selling, in a brief self-reinforcing loop.
The Bank for International Settlements' review pointed to a combination of factors converging at an unusually vulnerable moment: light liquidity typical of the Asian session, a cluster of options-related hedging flows and stop-loss orders sitting just below the market, and automated trading algorithms that reacted to the initial move by selling further, amplifying rather than dampening the decline. Once the price snapped back, the automated systems that had exacerbated the fall also helped it recover quickly, since the shock wasn't founded on any change in genuine information about sterling's value.
The episode reinforced a lesson already learned from equities and Treasuries: currency markets, despite enormous daily turnover, can still see brief liquidity vacuums during off-peak hours, and automated execution systems can turn a moderate order imbalance into a headline-grabbing air pocket before human traders even see it happening.
Further reading
- Bank for International Settlements, 'The 6 October 2016 Sterling Flash Event'