Friday is shaping up as potentially one of the most volatile trading days in years, as scheduled changes in futures, options and other derivatives markets threaten to add to a frenzied trading month that has already had some of the biggest daily stock-index swings ever.

The S&P 500 rose or fell at least 4% in eight straight sessions this month, the longest stretch in history, according to Dow Jones Market Data. The stock index snapped that streak Thursday, gaining 0.5%. The Cboe Volatility Index, the Wall Street fear gauge known as the VIX, hit its highest level in history this week.

Traders are bracing in part because of so-called quadruple witching, the Friday near the end of each calendar quarter on which options and futures on both indexes and stocks expire simultaneously. Options contracts outstanding tied to the S&P 500 Index hit a record this week. More than $1.5 trillion worth of S&P 500 options were slated to expire Friday, about a third of the contracts outstanding, according to Trade Alert data.

“Right now I would say buckle in,” said Steve Sosnick, chief strategist at Interactive Brokers, on the next few trading sessions. “Those moves in both directions can really be exacerbated.”

Trading volumes, which have already been at near-record levels in recent weeks, tend to pick up on quadruple-witching days. On the last such day, Dec. 20, 2019, about 11.8 billion shares changed hands in the U.S. stock market, compared with an average of about 7 billion shares a day last year, according to Rosenblatt Securities.