split, tear, open
坼 centers on forceful separation: splitting, tearing, or opening something apart, often with a sense of cracking or breaking.
坼 combines 土 (earth) with 斥, which likely contributes the sound and the idea of splitting or opening. The exact historical development is uncertain.
The left side 土 is earth, and the right side 斥 looks like an axe splitting something. Picture the ground cracking open as if struck by a heavy axe.
For タク, imagine a tack being driven into the earth, causing it to split open: tack -> タク, and the ground tears apart.