It is describing an ocean and a situation involving dangerous tidal waves and talking about how a sea of sort is washing up more sand to suck in wet stones for them to be dug under neath sand.
C.A giant wave washing the ships back to the Cyclopes' island.
Explanation:
Odysseus and his men had boarded in the Cyclopes' island. And things turn worse, with Odysseus blinding the Cyclopes and taking his rams from him. When the Cyclopes came to realize it was him, he asked Odysseus to come back so that he will pray to the god Neptune for his safe journey ahead. But Odysseus refused, went his way and decided to leave. Then, angered Cyclopes picked up a stone and hurled at the men and the ship. It was this effect that was being described in the excerpt "...the sea washed up in the splash as the stone went under, the tidal wave it made swept us suddenly back from the open sea to the mainland once again..."
