Standard noise returns smooth hills. Ridged noise takes the absolute value and inverts it, folding valleys into sharp peaks:

ridged(x,y) = (1 − |noise(x,y)|) ^ sharpness

Layered as fBm, each octave sharpens the detail further. As a flow field driver, the sharp transitions at ridges create zones where nearby lines diverge dramatically — dense packing along the ridges, open breathing room in the valleys.

Key variables: sharpness (1 = soft ridges, 3 = knife-edge), octaves (more = finer crags), noiseScale (broad mountain ranges vs. fine texture).