So we all know that New Zealand is unstable. Literally. As anyone from Christchurch will assert. So it shouldn’t really come as a surprise that with all this up-ing and down-ing and to-ing and fro-ing of the land, that a river has changed direction. No, I don’t mean there is a river that runs uphill, but rather that the land under a river has shifted enough to make it turn around. That’s pretty crazy stuff. Like, at some stage in our geological history, the Nevis River has just stopped and then carried on in the other direction. Cooler still is that it is part of this river system: (Although the pillars of the Kings weren’t there the last time I checked).
Picture from here
So how do we know this?
It’s thanks in part to these guys who I wrote about in my last blog:
This story involves 3 rivers:
– The Nevis (which changed direction)
– The Kawarau (which the Nevis now runs into)
– The Mataura (which the Nevis used to run into)
(and I suppose I should mention that the Nokomai stream is the part of the Nevis which continued flowing the same way)
Photo from here
If there were an award for the best naming of a species, this would certainly be a contender: Galaxias gollumoides , aka the Gollum fish. There is even another very closely related species called the Smeagol fish.
Zoologists at the University of Otago have found that the Gollum fish in the Nevis have relatives in the Mataura River (to the south) but not in the Kawarau River, which the Nevis currently flows into. This supports the geologists’ evidence that in the Pleistocene (2 million-ish years ago) the Nevis used to run south through a valley between the Garvie Range and the Remarkables Range (the jagged mountains behind Queenstown).
As the mountains on either side grew, they pinched off the valley the Nevis was in. At the same time, erosion blocked off the Nevis, and caused it to run back the other way. This isolated the Gollum fish in the Nevis from the Mataura river where it used to run. The Nevis population has since diverged from the Mataura population, but is still closely related.
Species that today are found in the Kawarau are not found in the Nevis, yet are found in other tributaries to the Kawarau.
Photo from here