So about five years ago there was a big earthquake that occurred in the Kaikōura region
and it affected several thousand square kilometers of this area.
One of the big impacts of that earthquake was the landslides. Over 29 000 landslides were
mapped by us and our team that were caused by that earthquake. Some of those landslides
were relatively small, just a few rocks that fell from the slope, some of them were big and this is
one of the biggest ones that was generated by the earthquake. This is called the Leader Landslide.
So the Leader landslide's in the order of about 10 million cubic meters in volume. The mass moved
from the top up there, so where we're standing now used to be all the way up there, and you
can see from the helicopter in the background the scale of this landslide. The landslide came down
and it actually blocked the Leader River which is down below us, and the dam formed. And over
the next few months after the earthquake the water level in the lake behind the dam started to rise
and eventually in several big rainstorms after the earthquake the dam breached and washed out a whole
load of material from below the landslide. So the the earthquake didn't just cause big landslides
it also caused a lot of cracking. And so what happens because the landscape is now cracked,
it means it's more vulnerable to future rain events. The water gets into the cracks, it loosens
the material and it fails. So one of the things that we're doing as part of our investigation
into the impact of the landslides is we have to understand how these landslides formed, and
this landslide is really interesting the Leader landslide because it forms on the junction of two
main faults. And these are geological faults that ruptured to the surface during the earthquake.
The purpose of what we're doing here is we're trying to characterize the materials that form the
landslide so that we can understand the different geological materials that are in the landslide,
and we can sample the slide surface. So this material that we're standing on this,
10 million cubic meters, moved along a surface that's several centimeters thick.
That's pretty impressive that an entire mountain can move on these little thin layers and that's
the purpose of our drilling. The reason we're trying to get the slide surface is so that we
can then take that material in its core as a sample, and we can put it into the laboratory
and we can test it. And it gives us the strength of the material. And what we're
doing then is we're numerically simulating the earthquake as it happened to try to understand
what processes caused the landslide to occur here. So when we have this information we
can combine it with other information from past earthquakes in New Zealand and internationally,
we can then use that knowledge to try to forecast where else in New Zealand
similar conditions may occur and where we may have the potential to cause damage to people, property,
pipelines, roads - you know the infrastructure that's really quite critical. So what we're
going to do next is we're going to show you how we actually investigate the landslide.
I'm the actual driller on there, so I actually operate the machine and stuff like that.
I've been in this game for a very long time and travel around the world. Obviously the setup and
all that's the main part to drilling your hole and stuff like that. If you don't get that part right
the rest of it's not going to go right for you either.
Quite often with hard solid rock soft ,stuff won't follow it up, so you've got to stop
and then restart but if you can actually get the drill running quite smoothly and stuff like that,
you can actually go through clays and rock and pick the whole lot up in one hit.
My name is James Chapman, iIm a drilling contractor. We're doing a series of holes through
this to try and understand the slide plane or how the surface failed. It's quite a unique drill
rig. It's a heli-portable machine and it fits together like a a rather large meccano set.
You can fly this thing into the bush pretty much anywhere, assemble it without roads or transport,
and go to work. So the landslide is around about 50 meters to the slide plane, so as far as diamond
drill holes goes these are quite shallow. So we're drilling using a method called wireline
diamond core and we're using one of these puppies which cuts a rather large round hole.
This spins, we cut the hole and we retrieve the material that we cut over the top and it comes
up the inner tube. We kind of find working with scientists they're a bit more intense
and a bit more on to what's happening, so it's pretty cool seeing these guys really fascinated,
looking at the core that's coming out of the ground. So you know
they're wrapped to see the material and we're about to get it out of the ground.
What we do is those samples come out of the ground and we clean them up and photograph them while
they're nice and fresh. So here's an example of one of these core boxes. This is from about 74
meters deep from the Leader landslide borehole. And what you can see here is just nicely wrapped,
this is a an example of the siltstone and this particular piece is from the intact ground
beneath the landslide. You can see it's a nice consistent piece of core, there's only a single
fracture in there. If we were to look at some of the material from within the landslide itself
it would be very broken up, there's lots of fractures, lots of clay and veining in there.
For the moment they're just going to stay stacked on site here and then in a few weeks time we will
take them down into a big shed where we'll open them up and we'll make detailed logs of the
material in the in the core. And then others are going to come along after that and they're going
to sample the interesting bits and do some tests on them to get some more information.
So this work is going to be combined with the geophysical survey and what we can do from there
is build models of these landslides that give us a really good idea of
how these things work mechanically, and how these materials fail in response to an earthquake. They
then run a series of tools down the hole which are the logging tools running behind me and they're
quite technical as to what data they recover so that assists these guys trying to understand why
these landslides occur, why they fail and how they fail.
So geophysics is essentially measuring the physical properties of the rock remotely. So
I can measure those properties with instruments on the surface, but what I really want to do is get
into the rock through a borehole and see them in situ. So the drilling is designed so that we get
our hands on the rock and we get a chance to look down into the hole by running these instruments.
Density - how much a rock weighs - that tells us a little bit about what type of rock it is
and what's happened to that rock. The other physical property that we look at is how
seismic waves propagate through them. So how will this hill respond if another earthquake happens.
So all this information is coming together in essentially a whole picture of what this hill
looked like before, what it looked like during it was sliding, and what it looks like now.
There are a lot of landslides that came down during the Kaikōura earthquake,
far more than we could possibly measure, so we looked at a few of them in detail. And the
idea is we chose a nice cross-section of ones - different rock types, different hillsides,
different sizes and we then have a catalogue that we can then compare other ones to.
This is the Stanton landslide. This headscarp up here is where you know the original
line of the land was up near the pine trees and all that has come down.
This hole is about 60 metres deep. The key thing is we drilled through the landslide then
we penetrated through the zone of the slide plane which we believe the rocks moved along when they
came down the hill. And we get below that so we're into what we call country rock or intact rock
below the landslide. Prior to the drilling we did some ground geophysical surveys on the landslide
where we laid out cables on the ground as a type of electrical survey where we inject electric
current into the ground and then we measure the voltage. And the resultant is 'resistivity'
which is a physical property of the earth. The bright red colours are high resistivity,
the greens at the bottom are rocks that are much more conductive, so they conduct electricity
really well, and it's a contrast the boundaries between these rock types that we are interested in
from the point of view of mapping the landslide. Now we get an idea of its complexity. So this
would be the landslide material and this would be the native material beneath the landslide.
All right so the drill rig is sitting on our line at about this location.
From our geophysical modeling we really don't know accurately how deep these boundaries really are.
So by drilling a hole down through this to about 60 meters we can then tag each of
those boundaries with the drilling. What's really important is that we cover the full depth range
so we understand where the big boundaries are but also that we get the detail from the borehole that
we can't see in the geophysics. By bringing all of these different pieces of the puzzle together it's
the only way we can really understand why this landslide occurred where it did. By investigating
these landslides we can then understand what caused them, why they are here, and we can
take that into other locations in the future to try to forecast where they they could occur.