2 December 2016

The North Canterbury Landslide Dams website

The North Canterbury Landslide Dams website

The aftermath of the Kaikoura Earthquake last month is increasingly becoming focused on the impact of the very large number (possibly over 80,000) landslides generated by the seismic event.  In common with other major earthquakes in mountainous areas, the immediate concern is focused upon valley blocking landslides – also known as landslide dams or quake lakes.  A small proportion of these can collapse rapidly, allowing the generation of a major flood / debris flow that can be devastating downstream.  Unsurprisingly, the Kaikoura earthquake has generated a large number of landslide dams, although none pose an immediate high level of risk.  The potentially more dangerous dams are being monitored by Environment Canterbury and GNS Science.  My old friend Sally Dellow is providing much of the technical coordination; I know of no-one better to play this vital role.

Canterbury Maps have now put together a wonderful web resource to provide information about the landslide dams – North Canterbury Landslide Dams – this is exemplary risk communication.  The site provides an interactive map of the location of the landslide dams, with the key dams being highlighted in red:

North Canterbury Landslide Dams

The North Canterbury Landslide Dams map of the major valley blocking landslides after the Kaikoura earthquake

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The site provides a table of information about the status of the key landslide dams as well, which will be updated as each reconnaissance flight is completed.  For example, one of the dams, Linton 340, is described as follows:

Dam remains intact, but face starting to erode. High chance of failure. Could affect some areas around Inland Road.

This is the image of the dam that the site has provided:

North Canterbury Landslide Dams

The Linton 340 landslide dam as photographed on 18 November 2016. Image via North Canterbury Landslide Dams

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These landslide dams are being managed in a very measured way.  Unfortunately they will present a substantial challenge for some time to come.

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30 November 2016

Earthquake induced landslides in the Himalayan mountains – new evidence for earthquake potential in Bhutan

Earthquake induced landslides in the Himalayan mountains – new evidence for earthquake potential in Bhutan

In terms of large earthquakes Bhutan has always been something of a conundrum.  The ongoing collision between the Indian and Eurasian plates that has generated the Himalayas occurs along a huge set of faults that run through the frontal range of the mountains and then dip below them.  It is this fault that generated the 2015 earthquake in Nepal.  Considerable work has been done to understand the palaeoseismology of this fault system, which has yielded a long history of large earthquakes – except for the Bhutan segment. There has been some very slender evidence of an earthquake in the early 18th Century, but nothing very detailed. This has led to speculation that this section of fault might behave differently in some way – perhaps that it undergoes slow slip to release the stress.

Bhutan

Google Earth image of Bhutan

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When I was in Bhutan a few years ago I raised the issue of earthquake triggered landslides with a range of people, to be told that there was no problem as Bhutan does not get large earthquakes.  I found that this troubling.  The country is very landslide prone, and the problem is becoming worse as the country develops.  Everything about the landscape suggests that earthquake triggered landslides would be a big problem during a large seismic event, and issue that has been emphasised by the Nepal and New Zealand earthquakes.  So understanding whether Bhutan suffers major earthquakes really matters.

I am glad to say that this problem appears to have been resolved at last.  In a paper published last month, Hetenyi et al (2016) reported archive and field work, and resultant modeling, that they have undertaken that has unearthed details of a large earthquake, likely to have been approximately M=8.0 (the range is 7.5-8.5), in Bhutan in 1714 AD.   The evidence includes a series of documentary accounts of the damage caused by the earthquake, and data from trenches across the fault that provide evidence of the movement.  From this information Hetenyi et al (2016) have modeled the earthquake to get an estimate of its likely magnitude.

To me this feels like a really important study.  We now know that the entirety of the Himalayan Arc has the potential to generate devastating earthquakes, and thus to suffer earthquake-induced landslides.  The implications for hazard management in Bhutan are clear.

Reference

Hetényi, G., R. Le Roux-Mallouf, T. Berthet, R. Cattin, C. Cauzzi, K. Phuntsho, and R. Grolimund (2016) Joint approach combining damage and paleoseismology observations constrains the 1714 A.D. Bhutan earthquake at magnitude 8 ± 0.5, Geophysical Research Letters, 43, 10,69510,702.

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28 November 2016

A revised landslide map for the M=7.8 Kaikoura earthquake

A revised landslide map for the M=7.8 Kaikoura earthquake

Valkaniotis Sotiris of the Earthquake Geology Research Group and the Aristotle University of Thessaloniki has posted a revised map of the landslides triggered by the M=7.8 Kaikoura Earthquake in New Zealand on his blog.  This map is available as a high resolution download:

M=7.8 Kaikoura earthquake

Map of Co-seismic ruptures and landslides from the M=7.8 Kaikoura earthquake in New Zealand

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To generate this map, which shows 5,875 landslides is a remarkable effort.  The maps of the density of landslides is particularly interesting to me:

M=7.8 Kaikoura Earthquake

Map of landslide density from the M=7.8 Kaikoura earthquake, via Valkaniotis Sotiris

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I noted in my earlier post that a reasonable first order estimate of the landslide locations can be obtained from the coincidence of the topography and the aftershock sequence.  This is a map of the aftershocks from the earthquake, mapped as a KML by Geonet.

M=7.8 Kaikoura earthquake

Geonet / GNS data showing the locations of the aftershock sequence triggered by the M=7.8 Kaikoura earthquake, mapped on Google Earth

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The coincidence between the two is not perfect of course (we would not expect it to be)  but the aftershocks are a surprisingly good predictor of the landslide distribution.  It would be interesting to know whether the aftershocks are a better predictor than the ShakeMap peak ground acceleration data.  The map produced by Valkaniotis Sotiris hints that this might be the case.

Other posts that might be of interest:

 

 

 

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21 November 2016

Siirt in Turkey: a desperate race to save the lives of miners buried in a landslide (with a video)

Siirt in Turkey: a desperate race to save the lives of miners buried in a landslide

Somewhat lost in the focus on the landslides triggered by the earthquake in New Zealand has been an ongoing landslide tragedy at Siirt in Turkey.  Here, a landslide on Thursday at the copper mine at Madenköy buried 16 miners.  To date the bodies of six men have been recovered, and operations continue to recover the other ten.  The authorities have admitted that their prospects are not promising. Heavy rainfall may have been a factor in the landslide, but to date six people have been arrested under suspicion of negligence, including the field operations manager of the mine and the owner of a subcontracting firm.

Remarkably, it appears that the landslide was captured on video.  This recording is on Youtube.  The panic and confusion of the person making the recording is clear:

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There are few images that show provide a decent view of the aftermath of the landslide, allowing a proper indication of the nature of the collapse.  This is the best that I can find to date, from the Haber Yerin news site (in Turkish):

Siirt

The location of the mining landslide at Siirt, via Haber Yerin

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Based on this image this appears to be a large, reasonably shallow rockslide in a heavily benched slope.  This image shows the debris pile at the foot of the slope, including the heavy equipment that was caught up and buried in the landslide, via Adana Kent:

Siirt

The heavy equipment caught up in the landslide at the foot of the slope at Siirt, via Adana Kent

 

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Unfortunately this is just the latest in a long line of mine related accidents in Turkey (this example remains one of the most remarkable landslides of the last decade), and of course I have highlighted previously the terrible toll that mine related landslides exact in some parts of the world.

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20 November 2016

Geonet commentary on landslides triggered by the Kaikoura Earthquake

Geonet commentary on landslides triggered by the Kaikoura Earthquake

Geonet has now posted an initial commentary on the landslides triggered by the Kaikoura earthquake in New Zealand a week ago.  I won’t seek to reproduce what they have stated, but the headlines are:

  1. There are between 80,000 and 100,000 landslides over an area of about 7,000 square kilometres.
  2. Based on an initial analysis of a new Worldview-2 satellite image there are 12 valley blocking landslides (landslide dams).

Many of these are likely to have breached naturally already, but all need assessment to this end, Geonet state that:

GNS has also started systematically flying landslide affected areas to visually identify landslide dammed lakes. The southeast flank of the Seaward Kaikouras, was flown on the 16th November and seven landslide dams were found. These flights will continue over the next three or four days. The purpose of these flights is to systematically cover affected areas where no data is currently available. The second purpose is to photograph the landslide dams to allow assessment of the hazard at each site.

The have provided a map of some of these landslide dams:

Geonet

Geonet map of some of the landslide dams following the Kaikoura Earthquake.

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Meanwhile, Environment Canterbury is now posting a series of videos showing aspects of the damage caused by the earthquake.  The Youtube channel can be found here.  Some of the landslides are impressive.  I particularly recommend the Waipapa Landslide video:

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This is a very deep seated slump on an unusually large scale:

Geonet

The unusually large large slump at Waipapa, via Environment Canterbury

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There is also a nice video of a large, complex and quite long runout landslide on the Leader River:

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Again, this appears to be a deep-seated slump.  Interestingly, in both cases the landslides have a very planar rear scarp:

Geonet

A deep-seated slump on the Leader River, via Environment Canterbury

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But the finest image is in the Geonet report that I cited above.  This is an image of the valley blocking landslide on the Hapaku River:

Geonet

The Hapaku River landslide, via Geonet

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As well as the very large scale of this valley blocking landslide, this image shows the vast number of additional landslides triggered by the earthquake.  Experience from elsewhere suggests that this number will increase in the first very heavy rainfall event after the earthquake.

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17 November 2016

Hapuku River: a major landslide dam after the earthquake in New Zealand

Hapuku River: a major landslide dam after the earthquake in New Zealand

With each passing day the impact of the Kaikoura earthquake becomes more clear.  Whilst human losses in this sparsely populated area were low, the major legacy appears to be the landslides, of which there are very many.   Resources are becoming available that provide detail, I would highlight the following as being particularly interesting:

  1. Canterbury Maps have put online a GIS map that provides details of their reconnaissance flights, and a large set of georeferenced photographs of the impacts, mostly landslides.
  2. The ESA has placed online a Sentinel satellite image that, though cloudy, allows many of the landslides to be seen.  The implication from this image is that landsliding is very extensive.
  3. The Research Group on Engineering Geology in Greece has posted a provisional landslide map, again using the Sentinel image.  This is not complete because of the cloud cover, but it starts to give an indication of what an extraordinary event this has been in landslide terms.  I think we can now safely say that this is the largest landslide events since the 2008 Wenchuan earthquake in China:
Hapuku River

Preliminary Map of Co-Seismic Landslides for the M 7.8 Kaikoura, New Zealand Earthquake, prepared by the Research Group on Earthquake Geology in Greece

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The landslide dam on the Hapuku River

At the moment the site that is causing the greatest concern is a landslide dam on the Hapuku River, which has completely blocked the flow and is about 150 m high.  This landslide was witnessed and photographed by a local resident, Neil Protheroe.  The Civil Defence has been circulating this photograph of the dam, and has advised those living downstream to relocate.

Hapuku River

The landslide dam on the Hapuku River as posted by Civil Defence

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There is a set of images on the Canterbury Government web server that I highlighted above, of which these are two:

Hapuku River

The landslide dam on the Hapuku River, image from Canterbury Maps

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Hapuku River

The landslide dam on the Hapuku River, image from Canterbury Maps

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The dam appears to be tall, narrow and, at least on the surface, comparatively fine grained.  The concern about the threats posed by this river blockage are not misplaced. More detailed analysis is urgently required, and will undoubtedly be underway.

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15 November 2016

Kaikoura earthquake landslides: the picture slowly emerges

Kaikoura earthquake landslides: the picture slowly emerges

As parts of New Zealand continue to reel under the combined effect of the ongoing aftershocks and the effects of very heavy rainfall, the effects and extent of the Kaikoura earthquake landslides are slowly emerging.  Much of the focus has been on the coast, and in particular the major landslides that have blocked SH1 and left Kaikoura itself isolated.  New images have appeared online of these landslides, which are undoubtedly dramatic.  This image was collected by Sargeant Sam Shepherd of the Royal New Zealand Defence Force:

Kaikoura earthquake landslides

One of the Kaikoura earthquake landslides by Sgt Sam Shepherd of the Royal New Zealand Defence Force

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Meanwhile some of the most impressive landsliding may well be inland in the Kaikoura Range of hills.  The landslide on the Dart Stream that temporarily blocked the valley drew some attention, and this is the first image that I have seen that gives a wider perspective.  It suggests extensive landsliding in the range:

Kaikoura earthquake landslide

A first image of Kaikoura earthquake landslides in the Kaikoura range

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I suspect that this is the location on Google Earth:

Kaikoura earthquake landslides

Google Earth image of one of the largest of the Kaikoura Earthquake landslides

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There will now be a great deal of interest in the extent of the landslides triggered by this earthquake.  You can get a reasonable first order estimate of this by comparing the location of the aftershocks to the topography.  As a very approximate estimate, the area with steep topography within the area defined by the main aftershocks will have been at a high risk of significant landslides.  This is GNS / Geonet aftershock data plotted on Google Earth, with the location of the valley-blocking landslide above shown:

Kaikoura earthquake landslides

The location of Kaikoura earthquake aftershocks plotted on Google Earth

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The map suggests that a substantial upland area may have been affected by landslides.  Of course this sort of approach is extremely rough and ready, and needs to be replaced quickly with proper field data, but it does give an indication of the magnitude of the problem facing New Zealand.

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14 November 2016

First news of landslides from the Kaikoura Earthquake sequence in New Zealand yesterday

First news of landslides from the Kaikoura Earthquake sequence in New Zealand yesterday

The large sequence of earthquakes in the northeast of South Island in New Zealand, the first of which was the M=7.5 Kaikoura Earthquake (this may actually have been a  pair of events), occurred in a mountainous but sparsely populated area.  New Zealand is highly landslide prone at the best of times, so it is unsurprising that there are initial indications that the Hamner earthquake sequence has triggered substantial numbers of landslides.

The first images of these landslides are now starting to appear.  The coastal region in the area of Kaikoura, seems to have suffered from a number of large landslides, blocking the state highway and railway line that run down the east coast.  These are key lifelines linking the Cook Strait ferries that go from Picton with most of the population of the South Island, including the city of Christchurch:

Kaikoura earthquake

Google Earth image of the northeastern portion of South Island

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There is an alternative road route, but it is a huge detour and crosses the Southern Alps in a pass.  But State Highway 1 is blocked with some substantial landslides, as this image, tweeted by Marlborough Emergency, shows:

Hamner Earthquake

Landslide on State High 1 near to Kaikoura, triggered by the Kaikoura Earthquake, as tweeted by Marlborough Emergency

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This is by no means the only landslide of this type blocking the coastal road.  This image was tweeted by SkyAlert:

 

Kaikoura earthquake

A landslide on SH1 near to Kaikoura triggered by the Kaikoura Earthquake and tweeted by SkyAlert

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Whilst this landslide has caused remarkable deformation to the railway line:

Kaikoura earthquake

Remarkable railway line deformation in New Zealand, via ABC News

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I wonder also whether these images are showing vertical uplift of the land surface, based on the shoreline platform.

There also appears to have been substantial landsliding inland.  One landslide is reported to have blocked temporarily the Dart River, although water is now flowing once more.  This image appears to show the landslide:

Kaikoura earthquake

A landslide blocking the Dart Stream in New Zealand, via the NZ Herald

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There appear to be other landslides in this image as well.

Finally (for now) there are some screenshots or remarkable landslides from footage broadcast by NewsHub.  This tweeted image appears to show a very large landslide:

Kaikoura earthquake

A screenshot of footage of landslides triggered by the Kaikoura earthquake, as tweeted

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This landslide appears to have left some very bemused cows:

Kaikoura earthquake

Cows left stranded by a landslide triggered by the Kaikoura earthquake

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Please post links to further images in the comments below.  In the meantime I suspect that the Landslide team at GNS Science are going to be very busy for the next few months.

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13 November 2016

Asakveien: a deadly quick clay landslide in Norway on Thursday

Asakveien: a deadly quick clay landslide in Norway on Friday

On Friday I posted about a dramatic quick clay landslide in Canada at the end of last week, which fortunately did not lead to loss of life.  Sadly, late on Thursday afternoon another event occurred, this time at Asakveien in Sørum municipality in Norway, with a much higher cost.  Aftenposten has a detailed article about the landslide, and its consequences, in Norwegian, but Google Translate does a pretty good job (with some minor edits by me):

At 5:45 pm on Thursday afternoon, the police received police notification that a mudslide had occurred in Asakveien in Sørum municipality, near a climbing park.  The landslide has a width of 400 meters and was almost 300 meters long.  Six forestry workers who work on a nearby farm were in the area where the landslide occurred.  Three of them escaped and reported to the police that three colleagues are missing.

It has now been accepted that the three missing men, all from Lithuania, have lost their lives, although the most recent reports suggest that their bodies have not been recovered as yet.

The newspaper images show that this is another classic quick clay landslide:

Asakveien landslide

The quick clay landslide at Asakveien in Sørum municipality, Norway, courtesy of Aftenposten and Hans O. Torgersen

 

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There is also some excellent drone footage on Youtube:

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There are suggestions, without any real evidence as far as I am aware at this point, that the landslide might have been triggered by construction, possibly associated with the road near to the toe.  This of course would not be the first case in which a quick clay landslide has been triggered in this manner.  There is a very interesting still from the video below:

Asakveien landslide

A still from a Youtube video of the quick clay landslide at Asakveien in Norway

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To the right of the landslide are both earth moving equipment and what appear to be cut slopes.  It would be most interesting to know if this activity extended into the area that failed.  Inference from the image above suggests that this might be the case.

Acknowledgement

Thanks to Odd Are Jensen for pointing this one out to me.

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11 November 2016

St-Luc-de-Vincennes: a spectacular quick clay (?) slide in Quebec

St-Luc-de-Vincennes: a spectacular quick clay (?) slide in Quebec

A spectacular landslide occurred yesterday (Thursday) morning at the village of St-Luc-de-Vincennes in Quebec, Canada.  Reports suggest that an area about 200 m wide was affected, and as a result several houses have had to be evacuated.

The best image of this landslide that I have seen is on Twitter, courtesy of Elizabeth Laplante, a journalist at YVA Nouvelles:-

St-Luc-de-Vincennes

The landslide at St-Luc-de-Vincennes in Quebec, Canada courtesy of Elizabeth Laplante on Twitter

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That is an impressive slide.  Xania News has this less good in terms of resolution but incredibly interesting image too:

St-Luc-de-Vincennes

The landslide at St-Luc-de-Vincennes in Quebec, Canada via Xania News

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And this is the debris trail, via Mireille Roberge on Twitter:

St-Luc-de-Vincennes

The debris trail of the landslide at St-Luc-de-Vincennes via Mireille Roberge on Twitter

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The shape of the landslide, with the narrow outlet and large bowl, plus the high mobility of the very wet, muddy debris, suggests to me that this might be a classic quick clay landslide.  It would be interesting to know whether works had been undertaken on the slope to cause destabilisation.  This is a Google Earth image of the site from 2013:

St-Luc-de-Vincennes

Google Earth image from 2013 showing the site of the quick clay landslide at St-Luc-de-Vincennes

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There is no sign of instability in the field, but note right at the toe of the failure, where the debris has entered the stream, there is an active landslide in the imagery:

St-Luc-de-Vincennes

Google Earth image of the toe of St-Luc-de-Vincennes landslide in Quebec

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It is possible that this landslide retrogressed, and then triggered the runaway quick clay (?) landslide.

Previous posts about quick clay landslides

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