Half action 1: burrow straight up 15' (I assume this requires a climb check)
Happily, that's still plenty enough to make a climb check (note that Genshior has Superior Climber, and so moves half speed instead of quarter speed when climbing).
Half action 2: burrow another 15', angling to break the cliff surface roughly 20 feet from karma (maybe 25).
Half action 3: Slam Attack 1d20+25=45
Note that with Blindsight Genshior is fully aware of Karma's location.
a Grab check
And since Genshior's pretty much got to make this check, I'll add an action die (d12?)
Action Die 1d12=1
total grapple check 54.