cliff
墈 centers on a steep natural landform: a cliff or precipice. The meaning is straightforward and tied to the earth.
墈 combines 土 (earth) with 勘, which likely contributes the sound. The character is used for a steep earthen cliff.
The left side is earth 土, and the right side 勘 suggests a steep, cut-away shape. Picture a sheer cliff face carved into the earth.
For カン, imagine a can perched on the edge of a cliff: can -> カン, and the can teeters on the steep drop.