The Bingham Canyon mine
landslide of a few weeks ago is an unusual mass movement. Kennecott Utah have put a set of very high
resolution images on their flickr site and have provided permission for me to
use them here (with due acknowledgement to them). I thought it would be interesting to take a
little time to examine this landslide in more detail. There is a great deal to
discuss here, so I am going to break this down into three posts over the next
few days.
So lets start by looking at
the site from a Google Earth image. This
is a vast mine – the excavation is 970 m deep for example.
This image shows the slope that failed before the collapse event. Note the machinery on the haul road for scale.
copyright
Kennecott Utah - used with permission
The landslide source area
This Kenncott Utah image shows the source area very clearly.
copyright
Kennecott Utah - used with permission
There are a
couple of really interesting aspects of this.
First, the headscarp has an unusual structure – I have annotated this as
point 1 in the image below. This
layering looks like a sedimentary structure.
I wonder if this might be waste material that has been dumped on the
slope? If you compare this with the before image above though this looks to be
just a small portion of the headscarp, so was probably not a key factor in the
failure event.
copyright Kennecott Utah - used with permission
Second, the
base of the landslide (2 in the photograph) is a comparatively planar
surface. This would suggest a
pre-existing weakness of some sort – maybe a fault? The orientation of this surface would have
made the kinematics of failure quite interesting. The landslide could not initially more down
dip because of the constraint from the valley wall, such that it would have had
to travel slightly along strike, making this a sort of hybrid wedge
failure. This structure could provide a hypothesis for the
two recorded failure events – the first was a detachment of a lower block,
which then released the upper block.
This is shown quite nicely from a zoom is on the upper portion of the
landslide from the fabulous overview image.
copyright
Kennecott Utah - used with permission
It is
clear from this that the trajectory of the landslide was controlled by this
basal structure. However, a comparatively small amount of material
spilled over the lateral boundary as well.
Sem comentários:
Enviar um comentário