11 momentous market days in the US in 2011

For most investors, August and September in 2011 were the most miserable – and memorable - months in nearly three years.

The stock market's volatile swings stunned investors, sending many into Treasurys. The market has not seen consistent volatility this extreme since the financial crisis in 2008.

Even more interesting, the majority of the most volatile days of the year occurred in these two months - right down to the last day of September, when the S&P 500 fell 2.5 percent and a key volatility index hit 43.

Click ahead to see the eleven most momentous days of 2011 - based on the S&P 500's percentage price change, trading volume and VIX level - and the events that made these days so extreme.