A mountain is a symbol of a great nation or power in many prophecies. It represents the strength of a mighty people or kingdom, as it does in the prophecy of Nebuchadnezzar’s Image.

Daniel 2:35
Then was the iron, the clay, the brass, the silver, and the gold, broken to pieces together, and became like the chaff of the summer threshingfloors; and the wind carried them away, that no place was found for them: and the stone that smote the image became a great mountain, and filled the whole earth.

The focus of this Trumpet is upon the sea. Again there is fire and blood, loss of life of those who live in this area and the loss of many ships. Again, the focus is on the “third” Western part of the Empire.

A prophecy concerning Babylon in the Old Testament refers to a political and military power or empire as a “destroying mountain”, even a “burnt mountain (or “burning” mountain” as it can be translated) . Most commentaries consider this (and the Second Trumpet prophecy) a description of a volcano (see samples below). The vision of the Second Trumpet is likely of an erupting volcano cast into the sea, and the key provided in this prophecy in Jeremiah shows that it represents a strong and destructive people conquering and controlling the Western Mediterranean. (Note the example in Gill’s commentary of Etna and Vesuvius, which indeed are to be found in the Western Mediterranean.)

Jamieson, Fausset & Brown
Jeremiah 51.25 “burnt mountain — (Rev 8:8). A volcano, which, after having spent itself in pouring its “destroying” lava on all the country around, falls into the vacuum and becomes extinct, the surrounding “rocks” alone marking where the crater had been. Such was the appearance of Babylon after its destruction, and as the pumice stones of the volcano are left in their place, being unfit for building, so Babylon should never rise from its ruins.”

Gill
“…and will make thee a burnt mountain: reduced to cinders and ashes by the conflagration of it: or, ‘a burning mountain’: like Etna and Vesuvius; we never read of the burning of literal Babylon, but we do of mystical Babylon: see Rev 18:8; and with this compare Rev 8:8. The Targum renders it, a burnt city.”

Keil & Delitzsch
“From what follows, ‘I will make thee a mountain of burning,’ i.e., either a burning, or burnt, burnt-out mountain, modern expositors infer, with J. D. Michaelis, that the prophet has before his mind a volcano in active eruption, ‘for no other kind of mountains could devastate countries; it is just volcanoes which have been hollowed out by fire that fall in, or, it may be, tumble down into the valley below, scattering their constituent elements here and there; the stones of such mountains, too, are commonly so much broken and burnt, that they are of no use for building’ (Hitzig). Of the above remarks this much is correct, that the words, ‘I will make thee a burning mountain,’ are founded on the conception of a volcano…”

Clarke
“Jer 51:25 O destroying mountain - An epithet which he applies to the Babylonish government; it is like a burning mountain, which, by vomiting continual streams of burning lava inundates and destroys all towns, villages fields, etc., in its vicinity.”

Barnes
“Jer 51:25 O destroying mountain - A volcano which by its flames and hot lava-streams “destroys the whole land.”