The apparent source of this waterfall: molten aluminum from the airliner's wings and fuselage, which had also piled up in that corner. Within minutes, portions of the 80th floor began to give way, as evidenced by horizontal lines of dust blowing out of the side of the building. Seconds later, near the heavily damaged southeasterly portion of this same floor, close to where the aircraft had entered, exterior columns began to buckle.
Fifty-six minutes and 10 seconds after it was hit, the top of the south building tilted horribly, to the east and then to the south, and initiated the collapse of the entire tower, floor upon floor.
Unfolding at a slower pace, the disaster at the north tower will require study before it can be explained in such detail. The plane entered the north tower between the 94th and 98th floors, the report says, destroying about 35 columns on its north face and wreaking indeterminate but probably substantial damage to the core.
The building stood for 102 minutes and 5 seconds.