A rare burst of volatility jolted financial markets and sent stocks and bonds tumbling Friday, a sharp shift from the tranquility that has characterized much of the nearly nine-year bull-market run.

The Dow Jones Industrial Average dropped 2.5%, its biggest one-day decline since the U.K.’s surprise vote to leave the European Union in June 2016. Meanwhile, the yield on the benchmark 10-year Treasury note climbed to 2.852%, its highest level since January 2014.

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