Psalm 46/Notes/Phrasal.v. 3.254181

Similar to בהמיר ארץ, the phrase (lit.) "in the toppling of mountains" (ובמוט הרים) represents the “verbal notion–subject” type (i.e., the toppling performed by mountains). In it, the preposition ב is also used temporally and should be rendered as when. Again, as before, the temporal clause ("when the mountains topple...") should be read as conditional (i.e., "[though] the mountains topple...").