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Wednesday, 7 December 2016

Landslide Dam

Seaward Slide, J.Thomson @ GNS science
Rockfalls and landslides were one of the dramatic consequences of the M7.8 Kaikoura Quake. This first photo shows one that is actually so huge that you might not at first recognise it for what it is. The white cliff in the distance is the landslide scarp and the huge green capped pile of grey in the middle distance is the debris that fell away. This landslide was of course made famous on TV by the cows that became trapped on an isolated hummock in the debris pile.

SH1 and Railway, Steve Lawson @ GNS Science
A large number of coastal cliffs collapsed, causing spectacular damage to the coastal transport infrastructure. In this image you can see how the raiway line has been lifted up and dropped across the road and across the beach.

J.Thomson @ GNS Science

Another example of rockfall damage along the coast:

Hapuku Landslide, Steve Lawson @ GNS Science

In the Canterbury ranges, a short distance inland, a number of landslides have blocked river valleys and created landslide dammed lakes that are now filling up. This image shows the massive Hapuku landslide, which has buried the valley in over 150 metres of debris, weighing many millions of tonnes. The grey coloured lake in the centre of the image is a couple of hundred metres long

Hapuku landslide, J. Thomson @ GNS Science

This is a close up view of the lake taken a few days later. The lake is now near to the point of overflowing the dam. The problem with these dams is that they can fail catastrophically, sending a debris flow of water, mud and rock down the valley with potentially very destructive consequences.

Linton landslide survey, J.Thomson @ GNS Science

In this image you can see another landslide, this time in the Linton Valley. It has also dammed a small river. The team here are surveying the debris and the shape of the valley in order to calculate the possible downstream consequences of a breach of the dam.

Linton landslide, J.Thomson @ GNS Science

This photo shows the size of the landslide.  A large section of forest has slid down with it with many trees still standing. The debris has again blocked the valley to form a lake.

Linton landslide dam, J.Thomson @ GNS Science

The lake level is still about 10 metres below the rim of the dam:

Linton landslide dammed lake, J.Thomson @ GNS Science

In order to measure the lake's water level safely, Chris Massey took a GPS reading from the helicopter whilst it hovered just above the water surface.

Linton landslide, J.Thomson @ GNS Science

Meanwhile at the base of the dam, some water is percolating through the debris, although the flow in the stream bed is much less than usual:
Linton landslide, J.Thomson @ GNS Science

This photo shows the toe of the landslide - a mass of rock debris and damaged trees.

Linton landslide, J.Thomson @ GNS Science

By the end of a few hours, we had lots of data in the form of laser scans of the slip from different locations, as well as hundreds of drone and aerial photos, which are combined to make a 3D digital image that can be used to model the possible consequences of the dam breaching in different ways.

This video made by Steve Lawson is a virtual 'fly through' of the digital model:


And here is a short video about these landslide dams:

Finally, there is more information about landslides on the GeoNet website here


Anonymous said...

Thank you for posting this information. It is very helpful in understanding the ongoing consequences of earthquakes.

Anonymous said...

At 0:39 - 0:40 in the Linton landslide video, the landscape still looks fairly dynamic. Clearly some courage required to be there even as earthquakes continue. Fascinating technology and information gathered. Thank you!

j4d3 goat said...

What amazes me is remembering that Lake Waikaremoana is a "landslide-dammed" lake! It must have been a *MASSIVE* landslide to have created that (and a HUGE quake to have triggered it!).

Anonymous said...