Many wind turbines contain a braking mechanism. This stops the turbine from overspinning, the runaway effect of which is:
That's a turbine in Hornslet near Aarhus, Denmark. Here's the same spectacular explosion from a more distant angle. Note how long it takes for the blades to fall to earth, and also the white van at the base of the tower.
Thankfully no-one was hurt, as a zone of 400 metres around the tower was evacuated.