"Come to nothing" here is an idiom meaning be completely destroyed. This phrase expands on the word "fall" and emphasizes complete destruction. Alternate translation: "mountains completely fall apart" (See: [[rc://en/ta/man/translate/figs-doublet]])
This can be expressed in active form. Alternate translation: "rocks tumble down from their place" (See: [[rc://en/ta/man/translate/figs-activepassive]])