Revelation 8:8

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;

Cross-reference

Revelation 8:7 describes the first trumpet's destruction on land — this second trumpet shifts to the sea, continuing the series.

Exodus 7:17-21 is the original plague of water turning to blood, prefiguring this trumpet judgment.

In Jeremiah 51:25, God calls Babylon a 'destroying mountain' that becomes burnt — Revelation 8:8 uses that image for a judgment on the sea.

Exodus 7:20 Allusion

Exodus 7:20 records Moses striking the Nile to turn it to blood — the specific event echoed in this trumpet.

Amos 7:4 Parallel

In Amos 7:4, the Lord's fire consumes the great deep — similar to the burning mountain thrown into the sea here.