cliffs
崿 centers on steep, rugged cliffs or precipices. The meaning is narrow and concrete, referring to a sharp, elevated rock face.
崿 combines 山 (mountain) with 咢, which likely contributes the sound and may relate to a sharp or jutting shape. The exact historical development is uncertain.
The left side is a mountain 山, and the right side 咢 looks like a sharp, jutting rock formation with a mouth-like opening. Picture a sheer cliff face on a mountain.
For ガク, imagine a climber on a cliff shouting 'Gak!' as they grab a hold: the sharp sound 'gak' cues ガク while clinging to the steep rock.