A lot of bitcoiners and altcoiners made a lot of money this year with the runup. If they cash out their profit before the end of the calendar year they (theoretically) have to pay taxes on their gains.
I'm guessing a lot of people are waiting until after the 1st of the year to sell their coins in order to cash out and realize a profit. Cashing out after the 1st of the year allows them one whole year to find tax havens such as mortgage interest and Roth IRAs.
Will people be selling a lot after the 1st of the year?