EMAS
"An Engineered Materials Arresting System (EMAS) uses materials of closely controlled strength and density placed at the end of a runway to stop or greatly slow an aircraft that overruns the runway. The best material found to date is a lightweight, crushable concrete. When an aircraft rolls into an EMAS arrestor bed, the tires of the aircraft sink into the lightweight concrete and the aircraft is decelerated by having to roll through the material."
Why didn't he sink through the surface the moment he entered the EMAS area? What good is an EMAS area if it has the bearing strenght to carry a loaded 738? The main wheels didn't sink through at all?