Linda- Hollow Wall

Linda banged the titacrete with her gauntlet and heard an echo from the other side. “Hollow,” she said. “Step back.”
...
She stepped forward and drove her titanium gauntlet through the titacrete, creating a hole a little larger than her fist. The roaring grew instantly more distinct and identifiable as the sound of a small waterfall. She punched four more times, enlarging the opening to about twice the size of her helmet.

-Halo: Shadows of Reach, Chapter 9