A huge ball of ice plummets through the atmosphere. The side closest to earth sees the most intense friction. The underside heats up to the point where ice transforms from solid to gas in nearly an instant and finally explodes. Intuition says that the side closest to earth is the hottest where the top is much cooler. Upon exploding the blast would have pushed away from the hot side. The cool side would have resisted and pushed the blast downward like a shaped charge.
We must take into account that upward air pressure resisting the fall would have resisted the downward blast pushing the blast away from the sides where the pressure of the slip stream is minimal. This would have tended to redirect the explosion radially. How much, I don't know.
Trees at the epicenter would have felt a downward pressure whereas the trees to the side would have felt a lateral pressure. I would have guessed that the trees at the epicenter would have been stripped of their branches.
I'm not fully satisfied with the ice ball theory. I'm not a believer in the spaceship theory. Any intelligence that can cross the galaxy should have better quality control against failure. The UFO guys have too many alien crashes for my taste to be believable.
I'm going for a natural event. One that can explode radially with minimal downward blast.
” I would have guessed that the trees at the epicenter would have been stripped of their branches.”
If the trees were not killed, a lot of new branches would likely grow in 20 years making the “grove” appear untouched.