Albert Barnes Commentary Psalms 104:32

"Who looketh on the earth, and it trembleth; He toucheth the mountains, and they smoke." — Psalms 104:32 (ASV)

He looketh on the earth, and it trembleth - There is great sublimity in this expression, as indicating the power and the majesty of God. He has only to look upon his works, and they stand in awe and tremble. The most mighty and fearful convulsions of nature occur as if they were the mere effect of God's looking on the earth. Compare Habakkuk 3:10: The mountains saw thee, and they trembled.

He toucheth the hills, and they smoke - That is, as Mount Sinai did when God came down upon it (Exodus 19:18). It is as if the hills were conscious of his presence, and were awed.