(8) The second angel blew his trumpet, and something like a great mountain, burning with fire, was thrown into the sea, and a third of the sea became blood. (9) A third of the living creatures in the sea died, and a third of the ships were destroyed.
By the sounding of the second warning, John sees “something like a great mountain,” and it is on fire. The burning mountain is thrown into the sea and a fraction of the sea became blood. Maybe it was the fire which rained down in the first trumpet warning which set this mountain ablaze. Whatever the case, this mountain is moved from its place and thrown out to the sea.
The “great mountain” which is burning with fire was first a figure used of Babylon: “behold, I am against you, O destroying mountain, declares the LORD, which destroys the whole earth; I will stretch out my hand against you, and roll you down from the crags, and make you a burnt mountain” (Jeremiah 51:25). The mountain in Revelation is likely a figure of the Jewish nation (which is also given the name Babylon later in Revelation).
The mountain is “thrown into the sea.” This is the figure which Jesus used to refer to the fruitless, ungodly Jerusalem of that day. In Matthew 21, after Jesus witnessed the fruitlessness in the temple of Jerusalem (v.12-17), he cursed a fruitless fig tree as a representation of the Jewish people who would receive the curses of the covenant (Deuteronomy 28). Then, to his disciples, he said “Truly, I say to you, if you have faith and do not doubt, you will not only do what has been done to the fig tree, but even if you say to this mountain, ‘Be taken up and thrown into the sea,’ it will happen” (Matthew 21:21). The “this mountain” is not just any mountain, but a specific mountain. Knowing that he was near the outside of Jerusalem, he must have been talking about Mount Zion (possibly as a figure of the Jewish nation as a whole). Later in the chapter, Jesus said to the Jews, “the kingdom of God will be taken away from you and given to a people producing its fruits” (Matthew 21:43). If the mountain of the Jewish nation would not bear the fruits of the kingdom, his apostles would ask that the mountain would be cast out and thrown into the sea, and it would be done. Here in Revelation, we are seeing the prophecy that it would soon take place in those days.
“A third of the sea became blood.” Water to blood was the first plague of Egypt, “The fish in the Nile shall die, and the Nile will stink, and the Egyptians will grow weary of drinking water from the Nile” (Exodus 7:18). However, in this vision, only a third of the sea becomes blood, and only a third of the sea creatures and ships were destroyed. This fraction which is affected is in keeping with the symbolism that the seven trumpets are only warning the people of a coming utter destruction if they don’t repent. Similarly, the plagues of Egypt appear to be warnings to Pharaoh.