What's bizarre to me is the assumption by the explorer that there was a passage to the deeper layers, sight unseen.
Usually, the method goes: we find a hole, it seems deep, I wonder where it goes. Let's get funding to find out.
His method was, let's take a hundred men, tromp about Siberia, and presume we'll find a hole.
Quite possibly an attempt to disguise an invasion recon expeditionary mission?
Various governments loved to use so-called zoological, geological, or geographical scientific expeditions as cover stories
for intelligence gathering from ~ 1800 until past WW1 - Rudyard Kipling wrote of it and popularized the phrase "The Great Game"...
it unfortunately led to many legitmitate scientific endevours to be blamed as "spies" !
yhs
prof marvel