Low volatility causes high volatility when inevitably, supply and demand finds itself in disequilibrium, which doesn't need any "reason" to happen.

The first circled section is the Chinese new Year's week, Jan/31--Feb/06, when banks were closed in China. The drop on Feb/07 may be people needing cash to pay bills. 
In the Chinese exchanges, that drop was only ~5%. It was followed by an ~8% drop on Feb/10, apparently right after Mark's "bug in bitcoin" announcement.
Curiously on Bitstamp the drop on Feb/07 was deeper than in China, about ~8%, and there was no drop on Feb/10. Perhaps because the West misinterpreted the Feb/07 Chinese drop as being some bad news from MtGOX, but laughed at Mark's claim on Feb/10?
In the second circled area, the drop on Mar/27 was clearly due to the Caixin leak about the PBoC "strenghtening" circular.
The small drop on May/11, after the third circled area, may have been the announcement by FXBTC that they were closing down.