In the photo of Steve with the Caribou horns on his back you can clearly see by the emblem that he is wearing “Muck” brand boots which are famous for their waterproofing and durability. However they are not very well suited for long hikes. They are slip on boots without laces. The conjecture in previous posts that Steve was not using waterproof boots is incorrect.
The waterproofing wasn't the problem. The lack of support is, especially in that terrain. But it also seems the waterproofing wasn't adequate for the task. Per Chet, SK's socks left in his tent were wet; it was 20 days before BC's feet returned to pre-tundra condition.
What I like about Chet's explanation, actually, is when he details exactly what he (Chet) wears to keep his feet dry. Layers and layers, and NEVER boots like that. He even trialed SK's socks.... Chet's layers include waterproof pants, gaiters, more than one baselayer (including one that is Smartwool)....
Chet aims for dry from tundra water, and doesn't care if his setup retains sweat: at least it's warm.
Perhaps even more importantly, waterproof muck boots are useless if water gets over the top. In tundra, it will.
Cotton pants—which it seems SK was wearing—would keep water in the boots. Not just an occasional drip, but a DRENCHING amount. See how he keeps his pants tucked into those boots? That cotton will soak up water like a sponge. Recall, the tundra is not just ankle-deep in water: it can be MUCH deeper. And the water is frozen ice. Every time SK stepped, he would have been squeezing cold water from the pants into the boots. They probably filled with water.
Also, Muck boots are neoprene (I have some, and I'm looking at them right this minute), except on the lower shin and foot, where they are rubber. Neoprene is wet-suit fabric. Yep, the stuff that keeps you warmer in cold water, but does not keep you dry (it keeps a layer of water against your skin). They are not water-proof breathable, and they are hellish hot, even in mid-winter. You'd want to be wearing very expensive socks, like Smartwool or Darn Tough of the really thick model.
So, yeah, Muck boots are theoretically designed to keep your feet dry, but not in AK or in the wilderness. People use them around here for farming, mucking out stables, getting maple syrup, places where you're unlikely to get an ankle roll. I only wear mine in the yard, and in snow. (They shred my feet; the only advantage is I can get them on quickly.) Maybe they use them for hunting in Kentucky, but I can't think they do much backcountry walking in them in rough terrain.
One very likely scenario for SK's disappearance is that he rolled an ankle, became incapacitated, and very quickly succumbed to hypothermia. The latter almost certainly happened (he'd only have avoided it if he was spirited to heaven), but a rolled ankle from inadequate support might very well have been a precipitating event.
