Huge spike in dow industrials volume

Just had a look at my charts. To my suprise I saw a huge spike in the dowi volune of 7B . Usually its around 400/500M. None of the other major US indexes had anythjng of that caliber. My question was a) is this because maybe more of the earnings to date were relavent to the dowi or b) is there something else going on under the surface. The move of the dowi wasnt anything signifcant soim just curious. Maybe a big company was being heavily traded? Any one know the cause. Im curious just because im on the look out for some type of distribution phase or money leaving the stock markets as a general consensus for the future so im looking for a sign. Thanks