Two cruise missiles striking in opposite directions at trajectories of about 10 degrees caused the gash at Shanksville. The first one struck creating a gash but the penetrating warhead did not detonate – it was embedded in the ground. The second one struck from the opposite direction and detonated a split second later, creating the center hole.
There are a couple myths that were likely spread to create confusion, but aren’t true:
THE GASH WAS ALREADY THERE IN 1994!
No, the gash was not there as was proved by the USGS photos.
GRASS WAS GROWING IN THE GASH:
Also not true. What you see are dirt clods with long grass growing from them that fell back into the trench after the missiles bored through the ground, one of which detonated sending dirt clods flying in all directions.