11 March 2015
In the last few days a video has emerged, via the Everett Herald, of the aftermath of the Oso landslide in Washington State, USA almost a year ago. The video, which has been uploaded to Youtube, was shot by Elizabeth Honnerlaw, who was driving on Highway 530 shortly after the landslide, and came across the aftermath. She shot the footage via her mobile phone – it runs for about three minutes:
The video is interesting at a number of levels I think. First, the video of the behaviour of the rear scarp of the landslide, which is the main feature of the video, is notable. The rear scarp was popping off small failures every few seconds. This is not particularly surprising – other videos have shown the same effect, caused by the over-steepening of the rear scarp and the loose, wet material from which it had been formed. It might be interesting to look at the location on the slope from which these landslide originated – I wonder if there is a consistent pattern in terms of the stratigraphic level? If so this might tell us something about the strength and degree of saturation of the various layers:
And the lack of dust in the air is interesting too. It doesn’t appear to be windy, suggesting that this was probably because the landslide did not generate huge amounts of dust, supporting the idea that the landslide was very wet at the time of the failure.
But the most interesting aspect really is the sense of calm. You might think that in the aftermath of the landslide everything was very chaotic, but this video shows a shockingly tranquil scene. There is a news report about the video on K5, which includes some additional footage, in particular showing the rescue efforts that were going on at the time. The small number of fire fighters, survivors and passers-by had started to try to rescue people caught on the edge of the landslide. Of course at this point the main rescue teams had not arrived. Apart from these well-organised rescue attempts – I have massive admiration for these first responders, who had to deal with a dreadful situation, and coped wonderfully – it would be impossible to know that the landslide had just occurred.
10 March 2015
27th February 2014 San Leo landslide
on 27th February 2014 a large landslide affected the historical town of San Leo, in the Montefeltro area of northern Italy, which I reported at the time. In a paper in the journal Landslides, Lisa Borgatti and colleagues (Borgatti et al. 2015) provide an overview of the San Leo landslide, including a historical perspective on large failures of the massif. There is no doubt that San Leo is both a spectacular location and somewhat prone to slope failures:
The town dates from Roman times; the churches were built in the 12th Century, as does the castle. Unfortunately, the spectacular setting means that landslides are inevitable – the limestone / sandstone block that forms the citadel is underlain by varicoloured clays, which provide a poor foundation, allowing movements to slowly develop in the main block.
The collapse on 27th February 2014 occurred on the flank of the limestone block, and fortunately did not destroy any buildings or strike any people. The best view of the landslide is from drone footage captured in a Youtube video:
Seismic data suggest that it occurred in two distinct events about 90 seconds apart. Borgatti et al. (2014) postulate a progressive failure followed by a topple event and rapid disintegration of the block:
But perhaps the most interesting aspect of the paper is this image, which compares a watercolour painted in 1626 by Francesco Mingucci with a modern day photograph from the same perspective:
Even allowing for artistic license the degree to which landslide has removed sections of the massif is very clear. In 1737 it is reported that a landslide from the block killed up to 100 people . These landslides will have profound implications for the preservation of this important historical site.
Borgatti, L., Guerra, C. Nesci, O. Romeo, R.W., Veneri, F., Landuzzi, A., Benedetti, G., Marchi, G., Lucente, C.C. 2015. The 27 February 2014 San Leo landslide (northern Italy). Landslides. Doi: http://dx.doi.org/10.1007/s10346-015-0559-4
9 March 2015
The online news agency Eleven Myanmar is reporting another serious jade mine landslide at Hpakant in Burma on Friday. The report suggests that a spoil heap 1000 feet (c. 300 metres) tall collapsed, burying a group of miners at the foot of the slope. As usual there is huge uncertainty about the number of people buried, but locals indicate that between 50 and 100 might be likely. It is probable that we’ll never know.
This is a Google Earth image of the area around Hpakant:
The devastation inflicted by the mining activities is clear to see. Al Jazeera has a very good article about the terrible social and natural cost of these jade mines, from which these two photographs are taken. Both show the slope conditions in which the miners operate:
This is the second major mining related landslide in Hpakant this calendar year, and there have been many before. That frequent landslides occur in such an environment is unsurprising; indeed I suspect that there are many small landslides that kill a few miners but are never reported. Managing slopes in mines is a huge challenge, but the expertise exists to do this properly. These landslide losses are absolutely unnecessary and deeply tragic.
7 March 2015
The work of excavator drivers in clearing rockfalls and landslides never ceases to amaze me. This is very dangerous work that requires high levels of skill, a deft touch and fast reactions to move out of the way of mobile debris. The work that these machine operators did clearing debris after the Kashmir earthquake in Pakistan in 2005 was impressive:
I’m not sure as to the origin of this video, which appeared on Youtube in the last few days. The video is on the Youtube channel of Abilitiazone Attrezzature, an Italian machinery company, but they seem to have many videos on there. Anyway, the video shows a large excavator trying to clear a very extensive rockfall:
It must have been a terrifying experience for the operator, who did a pretty good job of getting out of the way. The arm of the excavator was probably ruined, but at least the machine (and so the driver) was not buried and crushed.
4 March 2015
The last few days have seen unusually heavy rainfall across parts of the Himalayas and associated mountain ranges, resulting in reports of two valley-blocking landslides. The first occurred in the Reshun Valley of Chitral in northern Pakistan, and is very well reported in the Pamir Times, who have included the following images (amongst others):-
But this is a really odd one as the lake is quite large already, and the dam appears to have water flow over the top. I wonder therefore when this happened. Nonetheless, the volume of water trapped behind the blockage is substantial, so at least on the face of it there appears to be a substantial risk here. This shows the approximate location of the Reshun Valley, although the position of the landslide itself is not clear:
Meanwhile in Nepal there are reports of another valley-blocking landslide, this time in Humla in the west of the country. There is much less clarity as to the situation here. Republica carried the story yesterday, including some river gauging station data. Note though that as this station is a long way downstream it is not likely that the gauging station would show a signal of the landslide. But other reports suggest that the potential landslide is as yet unidentified, and that the main concern is a dramatic fall in the river level, which could be due to a variety of reasons:
Thousands of people living in the downstream villages of Karnali River Basin were put on high alert on Tuesday morning after the water volume in one of the two tributaries of the country’s longest river dropped significantly, raising fears of possible damming upstream.
Locals along with authorities in Humla district rang alarm bells after Limi Khola, which flows into the Karnali, recorded a dramatic 80 percent drop in water levels since Tuesday morning. Limi and Muchu rivers feed the Karnali.
“We have suspected damming of the river in the high altitude region along the Nepal-China border after the water level dropped significantly in the rivers flowing in Humla. However, we are yet to ascertain whether the river is blocked due to an avalanche or has frozen,” said Keshab Adhikari, deputy inspector general of police in the mid-western region, who is updating the situation in Humla.
The authorities are of course right to be very cautious as the water is being stopped by something, and will inevitably be released sooner or later. There clearly is an urgent need to find out what is going on upstream as soon as possible. I believe that this is the Limi Khola, the valley affected by the landslide:-
There is a nice description of the valley on this trekking website. The good news is that the catchment of the river looks to be very small, suggesting that the rate of inflow behind the blockage should be slow.
Of course the valley-blocking landslide in Zanskar in northern India is also unresolved so we may now be in a situation of having two or three serious landslide dams simultaneously.
2 March 2015
Gazost is a tiny village located high in the Hautes-Pyrenees region of France (43.031N, 0.007E if you want to find it on Google Earth). On Friday afternoon a reasonably large and quite mobile landslide removed 150 m of the only access road to the village, leaving the 20 or so inhabitants stranded. Reports suggest that the landslide occurred after a period of heavy snow in February and then rainfall more recently. France-3 has a nice gallery of images and a video of the site. This image provides a nice overview of the landslide:
This is quite an interesting landslide in that the debris appears to have been quite mobile. France-3 also has this image of the lower part of the track of the landslide:
The upper part of the landslide appears to be rotational, with a reasonably large displaced and back-tilted block:
Whilst the lower part seems to have been a mobile flow, judging by the materials at the toe:
27 February 2015
George Monbiot is a renowned writer and commentator, primarily on environmental and social justice issues, who pens a regular article in the UK newspaper The Guardian. I admire his work greatly – The Guardian is my newspaper of choice – primarily because he has an ability to see through clarity through complex issues. Interestingly, earlier this week he wrote an article focused primarily on the Harbury landslide, entitled “Our government’s big green idea: let’s subsidise natural disasters“. The point of the article is good and sound – he is making the argument that poor slope management in the uplands of the UK is increasing the occurrence of land degradation and landslides. I have no issue with this – indeed I welcome the observation. Upland catchments in the UK should be managed much more proactively to mitigate erosion, landslides and downstream flooding, rather than to the benefit of a small number of wealthy land owners. This will become more acute as the climate changes over the next few decades.
But, George Monbiot’s linkage of this issue to the Harbury landslide looks to be wide of the mark. He notes that in the years prior to the landslide Network Rail cleared the embankments of vegetation, most notably the larger trees. George Monbiot links this to the increase in landslides along the line:
“The Harbury cutting is one of the deepest and steepest in the UK. The satellite photographs show that in 2006 the slope was heavily forested. The next image, captured in 2010, reveals that the trees had been removed and it had been scraped from top to bottom. By 2012, when the most recent Google Earth image was taken, it remained bare and grey.
“Network Rail, which carried out this work in 2008, says it did so to protect the track. But grubbing out the trees, leaving the soil bare and scouring it vertically, without at least greatly lengthening the slope to reduce its angle, looks to me like a spectacular act of folly.”
And indeed George Monbiot is correct that Google Earth images do show the removal of vegetation from the slope during this period. This is the Google earth image from 2006:
And this is the 2012 image:
But look carefully at the images and you will see that this is much more complex than simple tree removal. It appears to me that the slope has been deliberately reprofiled, with the top layers having been removed, presumably to increase stability. In addition, it is very clear that drains have been installed. So this is self-evidently not a case of simple removal of trees, but rather a concerted effort to improve the stability of the slope.
And incidentally, it is quite reasonable and indeed sensible for Network Rail to remove trees from embankments. In the UK the embankments were frequently constructed well over a century ago. Stability in these cuttings is dependent on the drainage system, which is sophisticated (the Victorians were very good engineers) but vulnerable to disturbance. Large trees damage the drains, so it is sensible to remove them before this happens. Broken drains focus water at particular points, greatly increasing the likelihood of failure. And of course large trees can also fall onto the line, which represents a hazard in its own right.
And then of course we should take a look at the 2015 landslide. On Youtube there is a very nice video of the landslide taken from a drone:
What is clear from this video is that the landslide was very deep-seated – indeed, it was far too deep to have been affected in any significant way by the presence or absence of trees. So, the suggestion that this landslide was the result of removal of the vegetation is not correct, and is somewhat unfair on Network Rail, who face a very difficult challenge in maintaining this infrastructure at a time of falling budgets.
However, the more general point that George Monbiot makes about better management of the countryside in the UK is spot on.
23 February 2015
Fauquier Golf Course
The interesting Fauquier Golf Course landslide, about which I wrote over the weekend, does not appear to be a one-off event, although the most recent movement may well be far more damaging and significant than early events. This Google Earth image is dated January 2005:
Note the linear features running sub-parallel to the shoreline just below the clubhouse. These appear to me to be tension cracks and rear scarps. The other (less good) Google Earth image is from April 2009. Take a look at these features in this image:
The low sun angle does exaggerate the effect, but it is clear that four years on the landslide had developed substantially. The tension cracks and rear scarps below the clubhouse had become larger and more pronounced, and they had extended down towards the shoreline, especially on the right hand side. The landslide block is very clearly delineated.
Some of the Panoromio photographs give the game away. This one, by Kuschk, is entitled “Hill slumping on hole no. 4, Fauquier & District Golf Club”. It was taken in June 2010, and does very clearly show very large, fresh scarps:
Whilst this one, by the same person, shows one of the tension cracks and scarps that has extended across the fairway:
As is so often the case, this landslide event has been developing over a decade or more.
21 February 2015
Fauquier Golf Course
Fauquier Golf Course is located near Nakusp in West Kootenay, British Columbia in western Canada,on slopes above Lower Arrow Lake. This is the setting in Google Earth:
In recent days a large landslide has developed at the site, severely damaging some of the holes in the course. This news report describes the problem; there’s not much doubt that this is a landslide. There is a nice set of photographs of the landslide on the Daybreak South Facebook site, including these two:
The news reports suggest that the key opening time for the golf course at Faqquier is early April. Even if the movement has ceased getting the course playable by this time will be a challenge. The course appears to be an important source of revenue for the local community, so the effects of this landslide go far beyond the loss of a few rounds of golf.
19 February 2015
Paglajhora landslide video
There is an interesting video on Youtube from Paglajhora showing the collapse of a section of road:
Whilst this is not a new video (the accompanying text indicates that it occurred on 15th July 2010), I don’t think I’ve seen it before. The landslide apparently occurred at Paglajhora, on the Hill Cart Road connecting Siliguri and Kurseong in Darjeeling, northern India.
Paglajhora is described in a paper (Sarkar 2011) that is available online (NB PDF). This section of the Shiv Khola river is, according to Sarkar (2011):
“notorious for its slump/subsidence history that was initiated during the 1950 landslips in Darjeeling Hills…Since 1980, the incidences of slumping have become regular phenomenon, and by 1990 the Paglajhora slumps caused complete disruption of transportation and communication. The situation has deteriorated further in recent years”
The Paglajhora area is shown in the Google Earth image below; the yellow line is the Hill Cart Road:
The very extensive mass movement problem on this section of road is very clear, and indeed a closer view gives a better perspective on the serious nature of the problem at Paglajhora:
Sarkar (2011) suggests that the landslide problem at Paglajhora is the result of very weak colluvial materials, the origin of which is attributed to much older and much larger landslides. The nature of these postulated landslides is intriguing and deserves further study. These deposits were then reactivated by low quality construction and maintenance of the road and railway line, with poor management of the slope continuing to play a major role in the problems. The image above, from April 2014, suggests that the problem is not going to get better soon without proper management, and indeed the inevitable retrogression of the crown of the landslide is going to threaten settlements upslope soon. Perhaps the most shocking aspect of this is a comparison with the Google Earth image from January 2003:
The deterioration of the stability of the site in 12 years is remarkable. The morphology of the slopes in the 2003 image above would ring alarm bells to any competent geomorphologist or engineering geologist, and with good slope management it should have been possible to prevent this slope problem from developing. But, now that the instability has been initiated it will be extremely difficult, and expensive, to stop.
Sarkar, S. 2011. Evolution of the Paglajhora slump valley in the Shiv Khola Basin, the Darjeeling Himalaya, India. Geographia Polonica, 84 (2), 117-126.