nature

[altekake]

I've asked this question before but didn't get a satisfactory answer! When walking on the beach at the water's edge why is some of the sand hard and compacted, while other is soft? It is the same tide, wave action and wind!

[Old_Geezer]

Probably either a different rock, one that grinds down in sharp edges rather than little spheres. Or maybe one is a relatively new beach with larger grains.

[wildwood]

The hard stuff has only recently been exposed by the receding tide. It still has water logged sand underneath.

Have a dig in the soft layer and you'll find that not too deeply the damp sand is hard.

[Clanad]

Both the preceding answers have value, however, in an ancient, well worn College Level (here in the U.S.) Geology reference is contained a phrase: 'Wave Climate in Beach Stability'. It describes a study on the wave's action on beach sand, stating that (I paraphrase) wave action can be categorized by how strong it is. If waves are 'pounding' (not neccessarily large, however) the sand will become more compacted by reorganizing the
packing of the sand (reducing the spaces between the particles) and, hence, more resistant to foot pressure. If weather conditions haven't produced 'pounding waves', it's more unlikely the sand will be so compacted and therefore 'softer'...

Emphasizing what OG has stated; more rounded sand grains move past one another more readily than 'sharp' sand.