When the second angel blew his trumpet, a great mountain, as though it were burning with fire, was cast into the sea. If we consider Jesus’ words in Matthew 21:21 or Mark 11:23, it needs to be said that neither Jesus nor any of his disciples had ever prayed to remove a literal mountain and cast it into the sea. Jesus did cause a literal tree to dry up, but nothing was ever done to a literal mountain. Therefore, it seems to me that Jesus was speaking metaphorically, and, if so, he couldn’t have been speaking of Mount Olivet, as many commentaries assume. Rather, he spoke of Jerusalem in a spiritual or metaphorical sense (cf. Daniel 2:35; Zechariah 4:7). Jesus’ words: “this mountain…” was, probably, a gesture toward Jerusalem, which would have been in view from the point where Jesus and his disciples were standing and discussing the dried up fig tree.
If this reasoning is logical and true, the mountain mentioned in Revelation 8:8, which was cast into the sea would be Jerusalem or symbolically the Jewish nation, which included Judea and Galilee. Notice how Jeremiah puts it:
“Behold, I am against you, O destroying mountain, says the LORD, who destroys all the earth: and I will stretch out mine hand upon you, and roll you down from the rocks, and will make you a burnt mountain” (Jeremiah 51:25).
The prophet was speaking specifically of Babylon in Mesopotamia by whom the Lord destroyed Judah and many other countries (cf. Jeremiah 51:7, 20-23). However, Babylon in the Apocalypse is the spiritual name of the great city (Revelation 17:4-5, 18; 18:10, 16, 18-19, 21). This same city is the place where Jesus was crucified (Revelation 11:8). Jerusalem is the only city in the Apocalypse that is identified as the great city and is, therefore, Mystery (or spiritual) Babylon.
The roaring of the sea can refer to the great afflictions of the righteous (Isaiah 43:2), the trouble caused by the wicked (Isaiah 57:20), or it may refer to the approach of hostile armies (Isaiah 5:26-30; Jeremiah 6:22-23). Since the context of Revelation 8:8 doesn’t refer to complete destruction, but, instead, points to one-third of the sea becoming blood, it, no doubt, has in mind the great trouble caused by the wicked in Judea and Galilee during the time before Jerusalem’s war with Rome. Jesus promised to vindicate the righteous upon the heads of that very generation of Jews (Matthew 23:34-36). Therefore, all that the wicked would do to the righteous during this period would immediately come upon their own heads in the judgment of the seven vials (Revelation 16:1-21) in the form of the destruction of Jerusalem and the Temple in 70 AD.
Drawing upon the conclusions I’ve made in my study of the first trumpet, assuming that study is logical and true, this period of time between 56 and 66 AD was a period when law and order didn’t typify life in the lands of the Jews. It was a time when the high priest illegally killed James, the brother of the Lord, and others (cir. 63-64 AD) and escaped the judgment of the Roman governor through bribes. It was a time when some Jewish authorities were kidnapped and held for ransom and traded for wicked men, whom the Roman governor had imprisoned. It was also a time when Paul was illegally imprisoned in Jerusalem and remain chained, in order to please the Jewish authorities there. It was a time of persecution, when the poorer priests had their tithes stolen by the high priests, so that many of the priests died due to want, and believers began to apostatize, because of the intensity of the evil done to them.
It was a time of spiritual war, involving preaching of the Gospel in the face of false doctrine and persecution against those who preached Jesus. Some believers were killed by the sword, some were starved to death and some apostatized under the heavy arm of persecution, which may be the meaning of one-third of the sea becoming blood (Revelation 8:8). As mentioned above, the roaring of the sea may refer to the great afflictions of the righteous (Isaiah 43:2) or the trouble caused by the wicked (Isaiah 57:20). In the context of Revelation 8:8-9 the persecution against believers intensified in the 10 years prior to the Jews’ war with Rome, so more and more believers in the sea (i.e. in turmoil or persecution) died, and more and more of the ships (cities / churches) in the sea were destroyed.
Parts of a ship were often taken symbolically in Scripture (cp. Hebrews 6:19; James 3:4). Even Josephus, the Jewish historian of the first century AD, used maritime language to say “…many of the most eminent of the Jews swam away from the city, as from a ship when it was going to sink,” (emphasis mine). This was written concerning the time when the Roman army retreated from Jerusalem at the very beginning of the war. Thus, even Josephus likened cities to ships, and, if ships are cities, then it logically follows that the sea represents trouble in the land (cf. Isaiah 57:20; Lamentations 2:13). Finally, these cities can also refer to churches or synagogues of believers (viz. how cities and churches are used interchangeably in Revelation 1:11 and chapters 2:24 & 3:4). Thus, the turmoil into which Jerusalem was cast (Romans 8:8) was a judgment upon the nation due to the fierce persecution of believers by the Jewish authorities.
 If my earlier study: “Preparing to Blow the Seven Trumpets” is logical and accurate, then the context of the judgment against the mountain would be sometime between 56 and 66 AD, or the time between the imprisonment of Paul in 56 AD and the beginning of the Jews’ war with Rome in 66 AD.
 Josephus: Antiquities, 20.9.1
 Josephus: Antiquities, 20.9.2
 Josephus: Antiquities, 20.9.3
 See Acts 21:27-28; 24:5-6, 11-13, 18-21; 26:31-32.
 Josephus: Antiquities, 20.9.2
 Matthew 24:9-14.
 Josephus: Wars, 2.20.1