In an indirect way to answer this, there is an answer on bitcoin.org's FAQ. It states, the price follows the demand, when there is more demand for the coin, the price moves up and when the demand falls down, so does the price, just like any other commodity in general.
The circulation and creation of coins are (especially the creation is at a predictable rate), as the market is small it doesn't take much money to move the market price up and down, thereby making it more volatile.
I think the FAQ at https://bitcoin.org/en/faq# throws light on all such questions and answers.
