Pressure increases with depth when supporting a column of material. Applies to gasses, liquids and solids.
Collapsing From The Bottom
A stack of papers in Amazon boxes near my office door started to make a noise yesterday. I came around my desk to witness the sides of the bottommost box give way, causing a very unusual slump pattern as the boxes above fell. Of the stress of hitting the floor and each other caused about half of the boxes to also tear and suffer catastrophic failure.
If it weren't so much of a pain to repackage and repack, it'd be beautiful. As it was... sigh...
Always Look For The Silver Lining Label On The Inside
Of course if the slump had happened when the door was closed, I might not be able to get the door open. (grin)
So it could always be worse!