An-Nazi'at 79:32
The verse is a two-word sentence: "wa-l-jibāla arsāhā" — "and the mountains He cast as anchors." The root rasā comes from the language of seafaring: a ship dropping anchor and being held in place.
وَٱلْجِبَالَ أَرْسَىٰهَا
And the mountains, He anchored
An-Nazi'at 79:32 · Translation: talal-itani
Image
The Qur'an names the placement of the mountains through this nautical image. The condensed diction of the short sūras is compressed here into a single image: masses anchored upon a ground that moves.
Observation
In geology, the lithosphere encompasses the crust and the rigid outer portion of the upper mantle, and floats on the more slowly flowing asthenosphere. Mountain ranges are regions uplifted by compressive forces of colliding plates and constitute the thickest portions of the crust; the surface elevation is balanced by light 'roots' extending deep below. This principle of isostasy was formulated in the mid-19th century by Airy and Pratt.
Exegesis
Exegetes draw attention to the fact that "arsāhā" carries not merely the sense of "to place, to set down" but, like an anchor, "to fix in place." In the classical tafsīr tradition this verse is read within the frame of the "preparation of the earth" in Sūrat al-Nāziʿāt: the heavens were ordered, night and day were set, the earth was spread, waters and pastures were brought forth, the mountains were anchored — as the final link in a whole chain of settlement. Al-Rāzī recalls that the verse closes with "as a provision for you and your livestock": the mountain stands fixed not for itself, but for the one who lives upon it.
Sources
Tafsīr: al-Rāzī · Mafātīḥ al-Ghayb; classical tafsīr readings of al-Nāziʿāt 30–33.