[Daigoro]

On the physics front, I was thinking a high energy physicist or particle physicist, who might have theories to test about the nature of reality on the island. Your tellurgist, though, would probably cover the same ground.

As well as measuring gravity and EM propagation, he might try to observe radioactive decay samples. Bubble chambers, cloud chambers or spark chambers might still work effectively when electronics fail.

And he might be dreaming about getting a portable synchrotron onto the island to test CP-parity of kaons, although I don't think we can do that on a desktop device today, let alone in the 90s.

There are also secondary cosmic rays which can be observed at ground level, but I'm not sure how much he could calculate about them on the spot.