Albert Barnes Commentary Psalms 18:15

"Then the channels of waters appeared, And the foundations of the world were laid bare, At thy rebuke, O Jehovah, At the blast of the breath of thy nostrils." — Psalms 18:15 (ASV)

Then the channels of waters were seen - In (2 Samuel 22:16) this is, And the channels of the sea appeared. The idea is that, by the driving of the storm and tempest, the waters were driven on heaps, leaving the bottom bare.

In the passage before us, the word used, “waters” - מים mayim - would denote waters of any kind: seas, lakes, rivers. In the corresponding place in 2 Samuel, the word used - ים yam - properly denotes the sea or the ocean.

The word rendered “channels” means a pipe or tube; then a channel, or bed of a brook or stream (Isaiah 8:7; Ezekiel 32:6); and then the bottom of the sea or of a river. The allusion is to the effect of a violent wind, driving the waters on heaps, and seeming to leave the bed or channel bare.

The foundations of the world were discovered - They were laid open, manifested, or revealed. People seemed to be able to look down into the depths and to see the very foundations on which the earth rests. The world is often represented as resting on a foundation (Psalms 102:25; Isaiah 48:13; Zechariah 12:1; Proverbs 8:29); see the note at (Job 38:4).

At thy rebuke - At the expression of his anger or displeasure; as if God, in the fury of the tempest, was expressing his indignation and wrath.

At the blast of the breath of thy nostrils - At the breathing forth of anger, as it were, from his nostrils. See the note at (Psalms 18:8).