Volatility is back.

Stocks across Wall Street are enduring one of the most prolonged periods of turbulent trading of the past decade. So far this year, there have been 12 instances of the S&P 500 moving at least 3 percent from its intraday low to its high, according to data from Howard Silverblatt, senior index analyst for S&P Dow Jones Indices. Four of those swings were greater than 4 percent.

This figure is the most in a single year since 2011, when the European debt crisis flared up and Standard & Poor’s cut its rating on United States government debt.