“And the second angel sounded, and as it were a great mountain burning with fire was cast into the sea: and the third part of the sea became blood;”
King James Version (KJV)
8:8 And the second angel sounded, and as it were a great mountain burning with fire was cast into the sea - By the sea, particularly as it is here opposed to the earth, we may understand the west, or Europe; and chiefly the middle parts of it, the vast Roman empire. A mountain here seems to signify a great force and multitude of people. #Jer 51:25|; so this may point at the irruption of the barbarous nations into the Roman empire. The warlike Goths broke in upon it about the year 250: and from that time the irruption of one nation after another never ceased till the very form of the Roman empire, and all but the name, was lost. The fire may mean the fire of war, and the rage of those savage nations. And the third part of the sea became blood - This need not imply, that just a third part of the Romans was slain; but it is certain an inconceivable deal of blood was shed in all these invasions.
Re 8:8,9 THE SECOND TRUMPET. And the second angel sounded. Then the scene changes. And as it were a great mountain burning with fire was cast into the sea. Now a great burning mountain is cast into the sea. The sea is the theater of destruction. And the third part of the sea became blood. Again there is fire and blood indicating carnage and destruction. In the first judgment the third part of the earth suffers (Re 8:7); but now a third part of the sea. The symbols imply that some mighty volcanic power shall be turned upon the sea, and make it a scene of awful warfare and destruction.