This is the track that climbs up to the Mueller Hut above Mount Cook Village.
And if you don't have mountaineering skills and if you've not got a helicopter ride available
it's probably the easiest way to access the alpine environment above the plants where
there's just bare rock and snow and ice. So today we're going to come up here and have a
look at some of the processes that are going on in these high mountains the spectacular peaks of
the Southern Alps. So we're nearly up at the top and we're going to take a closer look from here.
How good is that! The weather forecast is really bad for this afternoon so we're just up here for
the morning. And we could of course stay in the bad weather to show you what that looks like but
I think we're going to go downhill instead and avoid it. So let's take a closer look.
So we are just below the Mueller hut and that's several hundred metres up above
Mount Cook Village. And really it doesn't get more spectacular than this view that you can see behind
me. This is Mount Sefton and this is the East Face of Mount Sefton. And so the edge that you can
see - the skyline edge there is the Main Divide of the Southern Alps, Kā Tiritiri o te Moana.
Why are these mountains here? Well that's because we have a plate boundary
which is a massive faultline just to the west of these mountains.
And that is the Alpine Fault. it is several hundred kilometres long, it's an enormous fault
and it creates Great earthquakes - often greater than magnitude 8 - roughly every 300 years.
And so the Alpine Fault - if we average out the movement along that fault - it averages
at about three centimetres horizontally and one centimetre vertically per year and that
vertical movement has built up these mountains over the last five or ten million years.
So the rocks that we see here have been uplifted from kilometres deep in the Earth.
There are metamorphic rocks they're made of schist because they've been heated under great pressure.
And they've been lifted up along the Alpine Fault to create these mountains.
And the reason that they're not kilometres higher than they are now is because of the erosion that's
been happening while they were created. So the Main Divide runs along approximately at a right
angle to the main air streams coming across the South Island from the west, and these air streams
are very moist - it's air that has come off the Tasman Sea - and the mountains are pushing that
air up and over the top of them. So as the air rises the pressure decreases, as the pressure
decreases the temperature goes down, and as the temperature goes down the moisture in the air
can't be held as vapour anymore so it precipitates as snow on these high mountains.
The snow falls down, it piles up year by year and these piles of snow turn into ice and become the
rivers of ice, the glaciers, that you can see all over that mountain face behind me.
So the glaciers are incredibly heavy. They're picking up rocks
at the bed of the glacier and grinding like a great big rasp carving away at the bedrock below.
So all of this rock material comes down with the ice and piles up at the foot of the mountain and
either gets pushed further along by bigger valley glaciers, or when they've all melted away it just
simply eroded by river erosion. So right where we are now is an environment where, if you like,
the erosion is dictated by the temperature, the moisture in the air, the ice and the snow and also
the steepness of the slopes. So they're unstable and we occasionally get enormous rock falls coming
down as well as the ice avalanches that are pretty much daily pouring off these slopes as well.
So all of this is a highly active erosion zone. Everywhere we look around here,
that's what we're seeing - we're seeing rocks that are fragmented, they've been broken apart
by processes of heating and cooling, by water getting into the cracks, freezing,
expanding and wedging those cracks further apart until rocks can be split in half by this process.
We have a forecast for today of 120 kilometre winds up here which is not unusual,
so as the wind picks up grit that's another force of erosion up here. We have thunderstorms, and
when lightning strikes a rock the lightning strike will preferentially follow the ice into cracks
in the rock so it literally can just you know cause an explosion and blast the rock to pieces.
We've got these rocks that have just been scoured out by ice and then as the ice retreated it
just left these boulders scattered all over the surface here. And in places we can see
glacial striations where as the ice was moving and dragging rocks with it, it it sort of carved
out grooves into these surfaces as well. So this is a very typical glacial environment.