Because the jets struck the World Trade Center Towers on the upper floors, the weight of the buildings caused their own collapse. As each concrete slab floor gave way, it smashed into the floor below. The massive downward crush of floors crashing, or
pancaking, on floors, sent out enormous clouds of debris and smoke.
At 10:28 a.m. Eastern Time, the north tower of the World Trade Center collapsed from top down, pancaking into dust.
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September 11, 2001:
Destruction, Reconstruction, and Monuments