Stock market fear is erupting as North Korea tensions mount

The stock market has been shocked back to attention by the escalating North Korean situation, and traders look scared silly.

The CBOE Volatility Index — or VIX, commonly known as the stock market fear gauge — burst from near-record lows on Thursday, spiking 44%, its biggest increase since May. The measure closed the day at 16.04, its highest level since the presidential election on November 8.

While the surge subsided slightly on Friday, the fear gauge is still up more than 50% over the past four sessions, its biggest increase since December 2015 for a period of that length.

What's more, trading volume in VIX options and futures reached all-time highs on Thursday, with more than 2.5 million contracts changing hands, according to CBOE data.

It's a stunning about-face for the fear gauge, which has been locked at historically low levels for the better part of the past three months. For a resilient market that's made a habit of shrugging off geopolitical risk, traders seem to be treating the looming nuclear threat as a different beast.

If so, that's bad news for investors who have been raking in easy profits betting on a stationary market. Through midweek, shorting volatility was one of the most crowded trades around. Now that the VIX is soaring, those traders may be forced to close their short positions, exacerbating the index's move higher.

Surges in the VIX are almost always accompanied by a decline in the S&P 500 — after all, the two indexes trade in opposite fashion 80% of the time — and that has certainly been true this week. The benchmark equity gauge slipped 1.5% on Thursday, its biggest decline since May.

Leading up to the slide, the S&P 500 went 15 days without a 0.3% closing move in either direction, the longest such streak on record. Those quieter days appear over for now.

Still, it's possible that traders will use this sudden weakness in stocks to add to bullish positions. It's a scenario that has played out many times during the eight-year bull market, and as recently as May.

On May 17, the S&P 500 plunged 1.8% in a single day, accompanied by a 46% VIX spike to 15.59. The benchmark stock index then ripped off seven straight days of gains, rising 2.5% and more than making up that loss.The VIX dipped back below 10.

The question now becomes: Is this time different?