There's fairly strong evidence that the rise from $6K to $18K was primarily the result of market manipulation [0], so in some senses it isn't a crash more like returning to normality. Although there is so much market manipulation going on it is hard to tell what normality is, e.g. the rise from $150 to $1K between Sep to Nov 2013 was due to the markus and willy bots [1]. That's one of the problems with a completely unregulated market where almost all the wealth has become concentrated in the hands of a few largely anonymous players.

[0] https://news.ycombinator.com/item?id=17302054

[1] http://uk.businessinsider.com/one-or-two-traders-may-have-ca...