- IJ
123: How was our cave entrance formed?
I have hunted the web for years to find pictures of other dry phreatic tubes and still haven't been able to find anything elsewhere worldwide that looks like our tube. Mainly because ours is dry, was previously empty before being filled in the last 30 years, and has no scalloping of the sides consistent with high velocity phreatic tubes yet still holds it's perfect shape without any vadose shape changes. Only at one bend is there any minor variation in one side and the floor. Now this tube was not hand carved - we could hit at it with steel picks and be lucky to make a hole 1cm wide and deep within an hour!
The diagram below shows various formations that can occur.
Our tube is an empty (b above) with a possible vertical bedding plane. It has not been filled with sediment at all as far as seems logical for such a phreatic tube. Ours was once empty before the earliest inhabitants (1000+ years ago) placed their dead inside and disguised the entrance. Only in the last century was it accidentally knocked open and then filled in by archaeologists and iwi once they saw what was inside would change history. Below are the closest photos I can find to what it would have looked like before being hand-filled in (which we are now digging out again).
The first photo is typical of the shape, but ours is generally much smoother. The second photo is as smooth but without the cracking in the walls and rounder in most sections.
Below is a shot of our tube showing shape and form of the roof and walls. At this location it was identical on the floor. Elsewhere there is evidence of bedding lines. You can see how old the surface is compared to the photos above.
The rumour of the skeletons in the cave behind this filled tube also mentions they were lying on 'cut shelves'. We know you can't 'cut' this material easily. Could this mean as a result of partial keyhole shaping further in where the water suddenly dropped away away underneath the tube? Unlikely, but if it was the case, it could actually look like this...
So the debate is still on as to how it was created, how and why the flow stopped suddenly and how old the tube it is. Being perfectly dry (is it only damp now due to our breathing) this would have led to the perfect place to store bodies and we suspect the skeletons we find will be in perfectly preserved condition and my guess is at least 1200-1500 years old - at least.
But that's a guess, we still as yet cannot produce the evidence we seek.
