Is there a relation? Does high volume often indicate that bitcoin will change it's price more drastically?
The average price of a BitCoin, if I understand correctly follows the following equation:
Price of an average BitCoin = Total Market Capitalization of All BitCoins / Number of BitCoins
If people are selling BitCoins for more than they paid for it, the price goes up. If people are selling BitCoins for less than they paid for it, the price goes down.
"Price of an average BitCoin" is just layman's way of saying "Weighted Market Price of BitCoin".
Volume is just how much buying and selling going on. It doesn't tell you if people are selling up the price or selling down the price.