NGB karst - extended push, turned back at ~3.2km

good writeup. the variance in symptoms between party members is interesting, physical vs psychological split makes it harder to pin on a single environmental factor.

what instruments did you have for gas? asking because CO2 buildup can produce both the physical symptoms (headache, nausea) and some of the psychological ones at higher concentrations, and selenite environments can trap it. though you'd typically expect either everyone affected similarly or the physically smaller people worse, not a split like you're describing.

the bone conduction thing Phil described, did it have any directional quality? uniform through the skull or coming from a specific direction? if there's a resonance chamber ahead it might be possible to triangulate roughly.

multigas — O2, CO2, H2S, CO. all within normal range throughout. CO2 was slightly elevated at 2.4km compared to entrance but not at levels that would explain what Phil described, and it didn't trend upward as we pushed further. O2 was fine.

i asked Phil about this specifically. he said it felt like it was coming from ahead and below — consistent with a downward-trending passage and something large further in. he was not certain about this. his recollection of the experience was not sharp, he said it was hard to think clearly enough to observe carefully while it was happening.

selenite resonance is real but i've never seen it produce effects at that distance from a formation unless the chamber geometry is exceptional. you're describing something affecting people 3km from the entrance and getting stronger with depth, if it's acoustic/infrasonic the source would need to be very large or very energetic.

infrasound is actually the more likely culprit for the psychological component. there's decent literature on infrasound-induced dread and paranoia, Vic Tandy's work in the 90s, a few others since. frequencies in the 18-19Hz range can produce exactly what you're describing. the bone conduction sensation could be the same source at a subharmonic.

do you know if any of you had unusual experiences in the 2-3 days after? some infrasound effects are reported to linger. also curious whether the effects were worse on second entry for anyone — if it's resonance-based you'd expect some physiological sensitization.

Dani had trouble sleeping the night after we got out. said she kept feeling like she was hearing something just below what she could actually hear, her words. gone by day two. the rest of us nothing notable.

yes, significantly faster onset for Reeves and i on the return push. would support the sensitization idea.

i've been reading about infrasound since we got back. the Tandy stuff is interesting. the chamber we're dealing with, if it exists and if it's the source, would have to be substantial. the airflow at 3.2km was strong enough that there's clearly significant void ahead. consistent with something large.

late to this thread. is the survey data to 2.3km publicly available or NKS members only? doing some work on selenite formation distribution in Shield karst and this would be useful to cross-reference.

NKS members only for now — it's in the registry under NGB-K-04. if you're not a member, dues are on the homepage. standard restriction for unexplored systems, you know why.

found this thread through a link and have a few questions if you don't mind.

you mentioned the bone conduction sensation felt like it was coming from ahead and below. when Phil experienced this, was it consistent throughout the affected zone or did it intensify at certain points in the passage — junctions, pinches, formation clusters? asking because infrasonic standing waves in selenite environments would have nodes and antinodes, and if the sensation tracked with passage geometry that would help narrow down whether it's a standing wave vs a continuous source.

also — the selenite formations you described. do you have any sense of their orientation? specifically whether the crystal growth was predominantly vertical, horizontal, or mixed? selenite crystals can act as resonance chambers themselves at certain aspect ratios and the orientation affects which frequencies they amplify.

and the dread and paranoia — did it feel like generalised anxiety or was there a specific directional quality to it, like a sense that something was ahead or behind rather than a diffuse feeling?

those are pretty specific questions for someone who found this through a link. what's your background, Guest_8847?

acoustics and material science, some crossover into geophysics. been looking at selenite resonance properties in a research context and this description matches something i've been working on theoretically. not a caver, no intention of going there, just trying to understand what you encountered from a physics standpoint.

if the questions are too specific i understand not wanting to answer.

fair enough. i'll answer what i can from memory.

re: bone conduction, Phil described it as consistent through the zone rather than spiking at points. if there were nodes he wasn't sensitive enough to them to notice. i personally didn't experience the physical sensation.

re: crystal orientation, mixed, predominantly vertical in the trunk passage, but the deeper formations we saw at 2-2.5km had a more complex growth pattern, some near-horizontal plates intergrown with vertical columns. unusual for selenite, suggests multiple growth phases. we didn't document it properly because Phil was running survey and wasn't stopping for photos at that point.

re: the psychological component, for me it felt directional. ahead specifically. not a sense of being followed, a sense that i shouldn't go where i was going. Reeves said something similar afterward, said it felt less like anxiety and more like a warning, though he couldn't say what it was warning him about.

i'm going to say this clearly for the thread: if your research is pointing toward something that explains what we experienced, i'd genuinely like to know. the honest answer is we don't have a good explanation for the psychological effects and it's been bothering me.

Guest_8847 — if your research is relevant to this, is there anything published we could look at? not being difficult, it's just easier to evaluate if there's something to point to rather than questions going one direction.

nothing published yet. early stage work.

what you've described — the directional quality of the dread, the bone conduction ahead and below, the sensitization on re-entry, the variance between physical and psychological responders — all of it is consistent with a very large selenite resonance chamber producing infrasound in the 7-19Hz range. the psychological effects at that frequency range are documented and the physical effects are a function of body resonance, which would explain why some people felt it physically and others didn't.

what i can't explain from here is the source. a chamber that large producing that effect continuously would need either a very specific geometry to act as a resonator, or a persistent energetic input. selenite doesn't generate its own energy. whatever is driving the resonance is coming from somewhere.

thank you for answering the questions. it's been helpful.

a persistent energetic input in a Hadean formation. that's a sentence.

Guest_8847 — the NGB greenstone belt is 4.28 billion years old. if you're suggesting the chamber is resonating from a geological source that's been active since the Hadean eon you're going to need to say that more plainly or it sounds like you're being cagey about something.

yes. that's what i'm suggesting.

i don't have a better answer than that right now. if i did i'd be writing it up rather than asking questions on a caving forum.

Guest_8847 hasn't posted since. if you're still reading this and your research goes somewhere, i'd like to hear about it.