Six times in Isaiah, things “break forth” (patsach). The word means “break,” as in breaking bones (Micah 3:3), but in Zion the things broken always sing.
When you compile all the uses in Isaiah, it amounts to a cosmic chorus. The whole earth breaks into song (14:7); heavens, the lower parts of the earth, mountains, forests, and each tree (44:23); heaven and earth, as well as mountains break out in joy (49:13); the ruins of Jerusalem sing (52:9); so does the barren woman (54:1), and the hills and mountains, the trees joining in with clapping (55:12).
When God cracks creation open, it erupts in song.