the video i linked to shows the floor- no stones- sand-
Why are you crying out to Me? The time for pleading and prayer was over. The time for action had arrived. Tell the Israelites to move on (14:15). In spite of Israel’s unbelief, God commanded: Raise your staff and stretch out your hand over the Sea of Reeds to divide the water so that the Israelites can go through on dry ground (14:16).
It also shows artifacts that have been lying there unburied for thousands of years. The seabed is not soft there, regardless of its composition.