The light curve and dust-halo expansion curve of comet 17P are constructed, examined, and compared with those of other comets that experienced outbursts. The 2007 megaburst of 17P is unrivaled as the most powerful event of this kind on record. The proposed scenario for the megaburst involves an exothermic reaction caused by a transition of water ice from low-density amorphous phase to cubic phase in a reservoir spread below a pancake-shaped thick layer of 1014 g of terrain on the nucleus' surface. The resulting explosion jettisoned this layer of inert mass into the atmosphere as a major fragment that began to crumble precipitously into a rapidly expanding cloud of microscopic dust immediately upon the lift-off. Fewer than 50 events of this magnitude would consume the entire comet.
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