  Using a wire heater to ignite magnetic avalanches in fixed magnetic field
applied along the easy axis of single crystals of the molecular magnet
Mn$_{12}$-acetate, we report fast local measurements of the temperature and
time-resolved measurements of the local magnetization as a function of magnetic
field. In addition to confirming maxima in the velocity of propagation, we find
that avalanches trigger at a threshold temperature which exhibits pronounced
minima at resonant magnetic fields, demonstrating that thermally assisted
quantum tunneling plays an important role in the ignition as well as the
propagation of magnetic avalanches in molecular magnets.
