Albert Barnes Commentary Psalms 78:13

"He clave the sea, and caused them to pass through; And he made the waters to stand as a heap." — Psalms 78:13 (ASV)

He divided the sea ... - The Red Sea. (Exodus 14:21–22).

And he made the waters to stand as an heap - The word rendered “heap” means anything piled up, or a mound; and the idea is, that the waters were piled up on each side of them as a “mound.” See the notes at (Psalms 33:7). Compare (Joshua 3:13), (Joshua 3:16); (Exodus 15:8).