Ok taking a crack at it here....

First off there are 8 Zaps left and 7 Omes left...Zap must sit one person out. Zaps sat out Sarita and Ralph in the IC3 but that gets reset each episode, correct? So all are eligible to sitout. In the Zap6 pic we see: Steve/Steph/Sarita/Julie/Mike and Dave cheering on an unseen teammate. So there are 7 cast participating for each tribe.

After viewing the instructions of the chal and strategizing, it makes sense for the Zaps to sitout Krista and keep Ralph for the wood chopping monster that he likely is. That is unless there is some JP equalizing rule that each tribe must play 4 gals which screws everything up.

But I'm going to ASSume that it's Ralph vs Rob in the log chop showdown(makes for better TV)

Anyway the chal seems to be run in a relay setup with individual legs.

One leg is to run, grab shovel and dig something up? (likely a key set for a chest).

Note: There *might* be more than just the one chest...and/or more than one digging area for each tribe.

Another leg might be the retrieval of the hatchet. It doesn't just appear by magic in Rob's hands. Either Rob retrieves it from a chest/buried/? or someone else retrieves it from a chest/buried/? and hands off to Rob on his chopping leg.

The chopping leg does appear likely to be the final stage since there is the rope to nowhere that often unfurls a tribal banner or flag....or drops puzzle pieces for the other possibly 4 remaining cast on the tribe to solve, who haven't done a damn thing in the chal yet.

So I'm suggesting that there *could* be more unseen chest or more digging areas(for keys or hatchet) and there *could* be a raised puzzle bag that needs releasing by the chopped log-rope connection.

Problem with this spec...
Rob loves to be in the spotlight and the pivot point for the chal, calling the shots. And he loves to be the puzzle solver so he can look smart. The chopped log as the final leg of the chal fits Rob's M.O. whereas the puzzle drop scenerio does not...unless everyone gets to solve the puzzle?

But somehow the other 3 or 4 people in the chal have to be involved in this somehow beyond cheering and jumping up and down on the tribal mat.

How does this chal work?