But are either of them volcanic in nature? Remember the pillar of fire by night and the pillar of smoke by day. And magma inflation could actually have caused a rise in the land under the waterway which made it possible to rise enough to travel across before the magma chamber emptied and it sank below water level again. A perfectly logical scientific explanation.
It may be scientific, but it doesn't necessarily explain that is what led them to the Mountain of God. . . It does not have to be a volcano. Tsunami actions can uncover sea floor for extended periods before the sea rushes back as well. It could have been a miracle. The light and noise atop the mountain, as well as the bush that 'burned without being consumed,' may well be better explained by looking to electrical phenomena. . . much of which is actually depicted Paleolithic rock art around the world