Can't really be surprised about the last-half hour meltdown. This is a disaster for the market because the initial support level is now broken and October 10's low is the abosolute last level remaining. There are no more short-term support levels remaining. Technically, if you count the bodies and not the shadows, we broke down a long time ago. Doesn't look good for the market at this point.
S&P 500 1-day
S&P 500 3-day
S&P 500 10-day