Today I am driving up a farm track oops! on the West coast of the South Island of New
Zealand near Whataroa, and we are going to go and visit one of the most extraordinary
rock outcrops in the South Island of New Zealand. I think this is probably my...
...one of the top few anyway in the whole country, because it's got a massive sort of implication.
so I'm with my friend Marty who's very interested in nature and interested in geology and all sorts
of ecology and that sort of thing. And so we're going to go and visit this rock outcrop
at Gaunt Creek which is a little creek and I'll show you with the camera where that is - so that's
the valley in the distance and you might be able to see some cliffs on the right hand side. And
so what's going on here is that range of hills is the foothills of the Southern Alps
and at the foot of the hills is the Alpine Fault and the rock outcrop that we're going
to visit is a slice, like a vertical slice, through the Alpine Fault itself. So the Alpine
Fault is one of the world's greatest geological faults. It's a huge feature in New Zealand, it's
highly visible even from space as you can see in this NASA image where the white area is the
snowy mountains of the Southern Alps and on the western edge of those mountains you can see a
really straight line - because that straight line is the Alpine Fault and the mountains have been
uplifted alongside it to the East. It is also a plate boundary fault so it is actually marking
the line between the Australian Plate to the west and the Pacific Plate to the east.
We're just going to go up this gully to the little light colored outcrop there which is
the outcrop of the Alpine Fault and we're going to take a really close look and see what we can see.
It's a very bright sunny day but you can probably see a transition from a grey coloured
cliff up the top there getting kind of greenier and turquoisier down to this point here.
So let's have a close look. And if you look carefully you can see
the green grey rock here above, a more muddy
bouldery rock here - so it's got these chips of schist in it and the join between these two types
of rock is right here where my finger is, okay? So if you follow down there you can see the line
going up here and that is the Alpine Fault. So that means that this is the Pacific Plate
and this here is the Australian Plate and I can actually touch those two plates,
those two tectonic plates with my fingers right on the fault line.
The Pacific Plate goes all the way across to California. It's a huge tectonic plate.
The Australian Plate connects us under the Tasman Sea to Australia and into the Indian Ocean and a
whole huge swathe of the Indian Ocean. So this is the meeting point of a massive structural feature
of Planet Earth and the best place to see it in New Zealand - Gaunt Creek. So these
grey rocks of the Pacific Plate here have come up from possibly as deep as 30 or 35
kilometres below the surface of the Earth and they're thought to be about somewhere
like three to five million years old. Down there the temperatures are incredibly hot,
and they've been moving up at a rate of something like one centimetre a year on average. But that
doesn't mean they've been creeping up every year by a centimetre, it means nothing's been happening
for a long time for 250 or 300 years and then suddenly in an abrupt earthquake there's been
perhaps a metre or two of uplift and then it's been quiet for the next 250 or 300 or 350 years.
So the rocks have come from very very deep in the Earth where the temperatures and pressures are
incredibly high. These greenish grey rocks right on the fault are called cataclasite. It's really
soft and mushy - that's why fault lines tend to be eroded out of the landscape as a very clear
feature in New Zealand - lots of our valleys are along fault lines. We have straight valleys like
the Hutt Valley near Wellington, it's eroded along a fault line. So very soft rock has come
from great depths and the plate boundary or the fault line is dipping down at this steep angle.
So on the other hand this material that's underneath the cataclasite is very young. This is
actually glacial gravel that has been overridden by the deep material coming over on top of it.
So this stuff was laid down in the ice age when there were huge glaciers around here.
And the material has been sort of washed off by melt water off the glaciers and so it's a
kind of gravelly glacial deposit, about maybe 15 or 16 or 17 000 years old, something in that
range. So very very young compared to these much older rocks. What we're going to do now
is we're going to walk around the side of this outcrop and now if you come up to where I am:
We're looking at the fault that's been cut through at a different angle. So instead of going up on a
slope we're seeing it if you like from the front and it looks like almost a horizontal line.
Here's the gravelly Australian Plate, the the ice age gravels, here's the Pacific Plate
that's come out from depths and being pulled up by movements of the Alpine Fault.
You can really see this gravel quite well but it's all of these rocks have been
really crushed through these earthquakes. And if we look up the valley here, if you look up there,
you can see that the line of the fault kind of gets buried a bit by gravel and stuff
but the cataclasite forms a really nice little cliff which we can follow up in the distance.
What I'm going to do now is I'm going to get the drone out and just get a little bit of an
aerial view to explore what the fault looks like from above from a bit of a wider view.
And you can see Marty walking up the bottom of the cataclasite outcrop so he's pretty much
on the line of the Alpine Fault as he walks up the gully. And when we go right back like this
you can see that there is a horizontal line going across to the right of the screen. That horizontal
line is the Alpine Fault with gravels underneath with the mossy coloured planty vegetated area and
above that you can see the rocks of the Pacific Plate overlying the Australian Plate there.
What I'd like to do now is go and explore in the next gully around to the right because
that gully has been washed out quite recently and I don't think many people or
maybe even nobody has been up there to have a close look to see if they can find the fault
there. So that's what we're going to do next and we'll take the drone
and have another look as well with that to get an overview of the situation.
We're coming up into the gully on the right which has been quite freshly exposed over the last year
or two and straight away we can see at the bottom of the wall of the gully. You can see the gravels
and above them the blue grey rocks so the fault is cutting across horizontally across that gully.
And what we'll do now is we'll take a quick look inside the gully just to see what we can find
in as much as it's fairly accessible, we'll have a look. It kind of goes without
saying that we don't want the Alpine Fault to rupture right now - I think we'd be toast.
But here you can see it! A fresh exposure of the Alpine Fault possibly never seen before since it
was eroded by big storms in the not too distant past. And if we go right up close to this wall
you can actually see a crack line. So if we were to see the surface of that fault
it would be really interesting. I wonder if we can find a place
we can actually see a flat surface of it. We should have a look. ...some Pacific Plate to find
the slip surface at the top of the Australian Plate which is right there.
There you go - those lines there might be slickensides so if I find that on this surface
in situ...
It looks like it's going in this direction which is pretty much north - south. If you
can come in close I think we've got some lines in this direction which is the
top surface of the Australian Plate on the Alpine Fault. There it is.
So we're going to go back down to the relative safety
of away from these cliffs and maybe use the drone one more time to take a look around.
So here we go.
"take off"
And up we go! Now we're coming into the gully. You can see the fault there in the gully.
We were in the gully down there.
Okay what I'll do now is I'm going to fly straight back and up into the sky.
So I hope you've enjoyed watching this video and learnt a few things about the Alpine Fault.
What do you think Marty any comments so far? More than I've ever hoped to learn today I must
say! - Great stuff - awesome! Thanks for watching the video I look forward to seeing the next one.