I like these high volume days. Today's final volume across all the boards was 897,900, quite a bit higher than usual.

There is a theory that when a large volume spike happens it is because the big institutional traders are entering the stock and that scares off the usual smaller day traders that have been tossing the stock back and forth.

Some more on high volume days:

"In volume analysis, a volume surge acts as a signal of a change in the price trend. By using the up/down volume charting feature, you can easily see what part of the VMA surge is on the price upside and what part is on the price downside. Basically, the more red volume bars you see, and the higher the red bars are, the more likely it is that the stock market will reverse its direction and move upward.

As a rule, a large volume surge on the price downside indicates that the large institutional investors, attracted by low barging price, are buying up the stock's shares that small investors are selling. Once all volume of this nature has peaked, the price trend generally begins to reverse and move up again."

http://www.marketvolume.com/analysis/up_downside_volume.asp