Their slain will also be cast out,
and the stench of their dead bodies will come up,
and the mountains will melt away by their blood. Bible other translations

“will melt away by their blood.” The picture being painted is that there will be so much killing during the Day of the LORD that the blood will flow in rivers down the mountains and wash away the dirt in the same way that a huge rainstorm that lasts for days can wash huge areas of dirt and debris down the mountains. This is a difficult concept, and so many of the English versions nuance the text to read like, “the mountains will flow with blood,” or “the mountains will be drenched with blood.” But the actual Hebrew text is more graphic by being hyperbolic: that there will be so much blood flowing down the mountains that they will wash away. Revelation 14:20 says the blood flowing from the Battle of Armageddon will flow for about 180 miles. Jeremiah 7:32 says that there will be so many dead bodies people will be forced to bury them in the unclean valley of the Son of Hinnom, the Gehenna.

Commentary for: Isaiah 34:3