Three landslide-induced railway incidents in a single day

News today of three different incidents from around the world:
1. New Zealand
NZ Herald reports that a milk train hit a landslide in Manawatu Gorge.  Fortunately there were no injuries, or even a need to cry over spilt milk...



2. India
Bangalore Mirror reports that three coaches of the Thiruvananthapuram-Mangalore Express train were buried by a landslide in a narrow cutting at Mulunthurthy.  Three people were injured, plus there were some minor injuries during the evacuation.

3. Canada
Various Canadian newspapers report that there was a serious landslide-induced derailment of a freight train at St-Lazare in western Quebec.  The accident trapped the injured train crew in their cab, requiring that they were rescued by firefighters.  Heavy rainfall was reported to be the trigger.  The images of the site, from the Montreal Gazette, are impressive:

 

 Landslides represent  an important risk to railways in upland areas, and where extensive earthworks have been used.  Railway companies expend huge amounts of resource mitigating the threat, usually with success.  Incidents are quite rare, but previous examples described on this site include:
May 2010: 19 killed when a train struck a landslide in China;
April 2010: Nine people killed when a train was struck by a landslide in northern Italy;
July 2009: Four people killed when a train struck a landslide from a cutting in China;
Dec 2008: A train was struck by a flowslide formed from power station ash in Tennessee, USA;

Images of the Meager Creek landslide in Canada

The Meager Creek landslide in British Columbia, Canada on Friday was a very large and very energetic event.  The latest estimates suggest that it had a volume of about 40 million cubic metres, making it one of the largest slides in Canada in recent decades.  Indeed, the Vancouver Sun quotes Rick Guthrie in stating that the slide travelled at 30 metres per second over a distance of 10 km.

Some good images of this event are now available, despite the smoke-filled air (the smoke is from local forest fires).  Worth a look is the Global Winnipeg gallery of the slide here, from which these images are derived:

This image shows the location at which the slide entered the main valley and then spread.  Note the way that the trees on the far valley wall have been stripped off by the flow.  This is called super-elevation and is an indication of the speed of the flow.  To generate this degree of super-elevation the flow must have been moving very quickly.

This is a view from the opposite side of the valley looking up the main flow.  Note the small lake forming upstream of the blockage.  This problem has now apparently been resolved.

This image shows the flow path of the slide down the valley.  Again, note the stripping of vegetation up the valley walls, suggesting a very considerable flow depth.

This is the upper reaches of the main slide, giving a great perspective on the magnitude of the flow.

The very best images of the slide are available on the Flickr page of DBSteers, a member of the Search and Rescue team that flew over the slide.  The images are explicitly copyrighted, so I will not reproduce them here, but I strongly recommend that you take a look.  The page is here:


http://www.flickr.com/photos/dbsteers/

Take a look - you won't regret it!

Landslide at Meager Creek, British Columbia, Canada

Thanks to Robin Beech for the heads-up on this one.  CBC News is reporting a large landslide at Meager Creek, a hot springs area north of Pemberton:

"A two-kilometre-wide landslide has been reported near Meager Creek Hot Spring, about 95 kilometres north of Pemberton, B.C. The flow of rock and soil debris has covered a river in the area, causing water to become dammed upstream of the slide.  Authorities say an unknown number of people are trapped in the area, but there is no word on injuries."


This appears to be the Meager Creek area:

Image from here.  CTV has a very poor quality image of what appears to be a large slide:

 Even the most cursory look at the Google Earth image for this area shows that this is certainly not the first large, valley-blocking landslide in Meager Creek:

The strange similarity between the Attabad and the landslide in Oliver

Yesterday I posted in both the ongoing situation at Attabad (and I am glad to say that it now seems likely that the reported landslide at Shimshal was a false alarm) and the mud and debris flow at Oliver in Canada.  It is now reported that the Oliver slide was caused by the failure of an embankment retaining a small irrigation lake.  If that is the case then I assume that the lake is this one:

The damage, shown below in an image from the Vancouver Sun, does serve to demonstrate the destructive potential of lake collapses, and thus our ongoing concerns about Attabad:

Has anyone seen any decent images of the path that the flow took between the lake and the valley floor?

Impressive mud and debris flow in Oliver, British Columbia

Thanks to a number of people for bringing this one to my attention.  The community of Oliver in British Columbia yesterday suffered an impressive mud and debris flow that is reported to have destroyed five homes (images from the Vancouver Sun):

The flow has clearly come out of a deeply incised gully in the mountains:

A perspective view of the excellent Google Earth imagery of this area is rather helpful:

Two things to note here (the flow hit the area just above the "97" on the image above).  First the community that has been hit by this flow is located on a small fan that has been formed by this type of flow.  Second, the very narrow, deeply-incised channel mouth is the classic location for this type pf flow, where a blockage allows debris and water to accumulate, before collapsing to generate a flow.  It is interesting to note that this area has reportedly experienced unusually heavy rainfall this spring and early summer.

Possible pre-failure ground deformation at the St-Jude quick clay landslide in Canada

Sadly, it has been confirmed that the family reported missing in the landslide at Saint-Jude in Canada yesterday were killed in the basement of their house.  Interestingly, the area of road on the north side of the slide looks like this (this view is looking north, effectively standing on the slide looking across at ground that did not move):

Note the two large, very recent tarmac repairs extending right across the road.  The nearer of the two is very suspicious given its shape.  There are also other hairline cracks in the road - right in the foreground for example.  This one may have a small amount of displacement across it (the line is slightly offset) although this may well be just an artifact of the image.  However, compare the two repairs with the Montreal Gazette aerial view of the slide - in this case looking from the north towards the south (i.e. in the opposite direction to the Google Earth image:

 The larger of the two repairs is clearly visible in the image, which means that the lateral margin (edge) of the landslide is almost exactly where the other repair is located.  It may well be that slide was creeping prior to final collapse, although this is clearly no more than speculation at this time.

I am glad to see that the media reports are now calling this a landslide rather than a sinkhole!

Possible flowslide (not a sinkhole) in St Jude, Canada

The Canadian media is reporting the case of a "sinkhole" that developed in St Jude, 77 km to the north of Montreal, last night.  The sinkhole included a family house, with four people inside.  At the moment these occupants are reported to be missing. 

The Montreal Gazette has a photo gallery of the site.  One of the photos is this one:

Based upon this image this does not look like a sinkhole but instead to be a quick clay slide, probably in Leda Clay.  Such slides are not uncommon in this area.  I have covered a previous example in Norway on this blog.  The famous Rissa quick clay landslide in Norway is available as a video here if you want an idea of the extreme end of this type of failure.Quick clay slides often occur on very low angled slopes, and can be triggered through ground disturbance which causes the clay to restructure, allowing it to flow.

At the moment I am unsure of the exact location of this event, but St Jude is at 45.77 N, 72.99 W.

Hat-tip to Peter Weisinger for highlighting this one.

The Burgess Shale - its all down to landslides!

The Burgess Shale is probably the World's most famous assemblage of fossils, made famous in particular by Stephen Jay Gould's book Wonderful Life. In a nutshell, the shale contains an extraordinarily well-preserved collection of Cambrian marine fossils, now generally considered to be 505 million years old. The morphology of the animals is generally somewhat extraordinary:





Walcott Quarry, the site at which the Burgess Shale is exposed, is located in British Columbia in Canada. Whilst studies over the last century have, understandably, focused on the fauna of the deposit, in recent years there has been a growing level of interest in trying to understand why this assemblage of fossils has survived in such a remarkable state of preservation. Earlier this year, Gabbott et al. (2008) published a paper that examined the mudstone in which the fossils are located in order to try to understand better the conditions in which the fossils were able to survive. Interestingly, a key factor appears to the occurrence of "mud-rich slurries" that buried the fossils rapidly.

Preservation of intact marine fossils requires that a number of conditions are met. First, of course, the organism needs to be buried in order for it to be preserved. This burial cannot be too dynamic or the organism will be broken up, but must be rapid to avoid decomposition. Once buried, the conditions must prevent decomposition. Finally, the material must survive intact the long geological time period to the future - this will probably include burial to considerable depths, where there are both high pressures and high temperatures - the Burgess Shale is thought to have reached depths of 10 km below the sea bed, in which temperatures would have been in the order of 250-280 degrees C! In many ways it is amazing that so many fossils survive.

Gabbett et al. suggest that in the case of the Burgess Shale, burial occurred in a series of fluid debris flows that came down from the slope, which is thought to have been about 160 m tall. These mud slurries buried the fauna almost instantaneously, smothering them without causing them traumatic damage, although some movement during the landslide is likely. Burial was sufficiently deep (tens of centimetres) that they did not float free as gases formed during decay accumulated and were also below the surface layers of sediment, in which large amount of bacteria are active.

Gabbett et al. conclude that it was this rapid but non-traumatic burial that allowed such remarkable levels of preservation of the fossils, rather than chemical processes that inhibited decay. An interesting case in which landslides have proven to be a good thing (apart from the organisms themselves of course).

Reference:
S.E. Gabbott, J. Zalasiewicz, D. Collins (2008). Sedimentation of the Phyllopod Bed within the Cambrian Burgess Shale Formation of British Columbia Journal of the Geological Society, 165 (1), 307-318 DOI: 10.1144/0016-76492007-023

Highway 97 reopens

Highway 97 in Canada reopens today having been closed for 19 days. The construction teams have blasted 34,000 cubic metres from the crown of the landslide and have moved it to the toe. In consequence the slope has effectively stopped moving. The contractor will continue to monitor it to check that it remains stable, but the prognosis is probably good.

There is a terrific image gallery of the works here:


Well done to all involved.

Recent landslide updates

A few updates on landslide events over the last few days:
1. Highway 97: various newspapers now report that the teams trying to stop the movement of the slope are making headway. The rate of movement has now slowed to about 8 mm per day (half of the rates measured early in the crisis). The drilling and blasting crews have now moved 5,000 cubic metres per day from the crown to the toe of the slope. There are hopes that the road might be reopened within a week.
2. Pitrap, Poot District, Kenya: Two landslides struck this small village on 7th November, killing a total of eleven people, most of whom were women and girls who had gathered to celebrate the birth of a child. Heavy rain was the trigger.
3. Landslides in Yunnan Province, China. Xinhua has now published some images of the landslides in China last week that left at least 83 killed or missing:

Xinhua image of Dasongshu Village of Xishelu Township in Chuxiong Yi Autonomous Prefecture

Xinhua image of landslides in Yunnan Province. Note that a number of the landslides, which are all shallow, have started on or by the road

Xinhua image landslides in Yunnan Province.

4. Landslide in Hunan Province, China: Xinhua reports that six people were killed by a landslide in a landslide on 7th November in Huanxin Village, Pingjiang County. The landslide was triggered by heavy rainfall.
5. Landslide in Burma (Myanmar): This is a location in which I suspect that I do not manage to record all of the landslide events that occur, given the news black-out imposed by the Burmese authorities for much of the time. However, reports have emerged that a landslide on 28th October in Mongton Township, Southern Shan state killed 13 workers on a tea farm. The cause was heavy rainfall.

Highway 97 update

Blast on the problem slope on Highway 97 (from CBCnews)

Attempts to deal with the slope problem on Highway 97 in Canada continue in a quietly controlled manner, and there are now some signs of success. The focus continues to be upon small blasts at the head of the slope to remove material, which is then transferred to the toe to support the mass and to protect the highway. The size of each blast is now reportedly 2000 cubic metres. The result of this work is that the rate of movement has slowed from over 10 mm per day to 8 mm per day now. However, care is needed in interpreting these movement data as the reduction could be caused natural variation or response to another stimulus (the slope could be draining for example).

Meanwhile the road is still closed indefinitely, and Houdini the goat appears to be in good health!

Did you hear the one about a goat in a landslide?

A bit of light relief over at the Highway 97 site in Canada, which continues to slip. Arthon have a pictorial report on their website of the rescue of a mountain goat that had fallen down the tension crack and become wedged 10 m below the surface (all images from the Arthon website):



Fortunately, the goat (now named Houdini) was spotted and a rescue was put in place. Enter the gallant abseilers (you wouldn't mess with these guys on a dark night):


They abseiled down and tranquilised the goat, who was then hauled back to safety:


Meanwhile the slope is still moving 10-15 mm per day and as a result the road is still closed. A water taxi has starts on Saturday morning to allow people to get around the blockage.

Hat tip - Andrew Giles again.

Highway 97: test blast

The latest report on the Highway 97 problem in Canada (see earlier posts here, here and here) is as follows:

• The contractor, Arthon, released a statement to the press yesterday, the key points of which stated that "Highway 97 remains closed north of Summerland until further notice due to an unstable rock mass above the highway. The slope continues to move, therefore the highway is not safe to reopen. Safety is our top priority. The ministry is doing everything it can to reopen the highway as quickly as possible, but we won't open it until it's safe. We've built access roads to enable heavy equipment to reach the slope.
  Our first test blast took place this afternoon to help assess the stability of the rock mass.
  The geotechnical experts will now analyze the results of the blast and will have an update tomorrow afternoon. The results of the blasting will help the ministry finalize the work plan."
• The tension crack extended by 8 millimetres overnight Tuesday-Wednesday, giving a displacement of 3.3 cm since Sunday.
• The plan to move material from the crown to the toe of the landslide now appears to be the favoured solution. It is not clear how this will affect the road.

The cautious approach beiung adopted by the authorities is quite correct in my opinion.

Highway 97 latest update

The latest update on the Highway 97 landslide in Canada (see here and here) is as follows:

1. The slope is still moving. Between 19:00 on Monday and 14:00 on Tuesday the mass moved about 15 millimetres (i.e. about 0.8 mm per hour). This is quite high for a large mass. The rate of movement is described as being constant;
   
2. The mobile volume is now estimated to be 200,000 cubic metres;
3. The road remains closed (unsurprisingly!);
4. There are provisional plans to remove material from the top of the unstable slope and to move it to the toe. The aim here is to reduce the mass that is driving the movement and to increase the mass that is supporting it.

I am sure in the background there is an enormous amount of work going on. Analysis of the pattern of movement in time and space, especially by looking at vectors of movement and accelerations and decelerations will give a pretty good idea of what is happening in the slope. This gives a potential for providing a short term warning of an impending collapse, but does not really tell us how likely this is in the medium term.

Highway 97 update

Arthon have posted an update on their website of the situation at Highway 97 in Canada:

"Slight movement in Rock Mass overnight. Road likely closed until Thursday at a minimum. Options being considered for removal of rock"

There is also quite a nice news report with footage here. In the report there is a good description of the use of precursor indicators that can be used to warn of a large-scale failure. They are quite right that movement data, sounds, the opening of cracks and the occurrence of small falls can be used to indicate that a large slip might occur. However, they will need to understand the slope quite well before this option is adopted, and they will need to be particularly cautious when it rains or there is snow melt.

Arthon have published some excellent pictures, including a couple of aerial shots, here. The picture below is the best of them to give an oversight of the problem:

Click on the image for a link to the full size version. Note that a few metres below the main crack there appears to be a smaller tension crack running across the slide, perhaps suggesting that it is starting to break up a little.

Interesting slide on Highway 97 in Canada

Thanks to Andrew Giles for bringing this one to my attention. Highway 97 in British Columbia is currently being upgraded through the Okanagan Valley (Fig. 1). This project is being undertaken by Arthon - their project website describes this as:

"Four lane roadworks and 1,000,000 m3 rock removal over a 7 km section of BC's main north-south highway corridor. The B.C. Ministry of Transportation awarded Arthon Contractors Inc. a $38.6 MM contract to complete roadway construction by summer 2009".

Fig. 1: Google Earth image of the location of the problematic slope on Highway 97.

The rock removal appears to be a widening exercise in which a substantial amount of rock has been removed to create a platform. Unfortunately, last Friday the contractors noticed that a crack had appeared in the slope above the works at the location shown on Fig. 2.

Fig. 2: Google Earth perspective view of the area of the unstable slope before the slope cutting had commenced.

The crack in question is not insubstantial. I must note here that I am very impressed with the openness of those involved - the contractor has placed images on their website of the nature of the problem (Fig 3.), even showing comparison views of the crack opening.

Fig. 3: Arthon Ltd image of the crack on the slope (from the Arthon Ltd web page)

The block of rock that is moving is large - about 300,000 cubic metres (Fig. 4), with the crack at the rear extending downwards for at least 10 m.

Fig. 4: Arthon Ltd image of the mobile block (from the Arthon Ltd web page)

Unsurprisingly, the authorities have stopped both the work on the slope and the traffic on the road, and now it is a game of wait and see. One possibility is that the slope will collapse completely, it may keep creeping or it may stop. Whatever happens the authorities have quite a challenge on their hands to know how to deal with this slope. The pattern of displacement against time is one tool that could be used in this case.

I'll post again as this develops. In the meantime, congratulations to all for their transparency in this case.

A follow up to the Sea to Sky Highway landslide

Back on 1st August I posted about a landslide that had blocked the Sea to Sky Highway (Canadian Highway 99), which links Vancouver to Whistler, venue of the 2010 Winter Olympic Games. The road was blocked for a few days, but has now reopened.

Two sets of colleagues in Canada have very kindly provided follow ups to that post. First, Frank Baumann, who is a geotechnical engineer in Squamish has very kindly sent an image (Fig. 1) of the landslide for inclusion on the blog. This very nicely captures both the scale of the problem and the topographic setting of it.

Fig 1: Photograph (copyright Frank Baumann) of the Highway 99 (Sea to Sky Highway / Olympic Corridor) landslide in Canada.

Second, Steve Evans and Keith Delaney from the Landslide Research Programme at the University of Waterloo in Canada have very kindly provided the following explanation of the landslide, including this excellent comparison image:

Fig 1: Illustration (provided by Steve Evans and Keith Delaney from the University of Waterloo) showing the site of the 29th July 2008 landslide. The main image shows the site before the failure, the smaller image the site after. Inset is a stereographic projection plot of the failure surface and joint sets. Click on the image for a better view.

Steve and Keith write:
"The site of the July 29^th 2008 Sea to Sky rockfall/rockslide was examined in 1997. The main photograph in Figure 2 shows the site at that time. The photo at the lower right of Figure 1 was taken soon after the 2008 event by Canadian Press. The slope consists of resistant Coast Plutonic Complex granite but as seen on the 1997 photograph (and on the cover of the book “Rock Slope Engineering” by Hoek and Bray) the rock mass is characterized by more-or-less planar stress relief (sheeting) joints that dip west (downslope) towards Howe Sound (pole concentration is red dot on the stereonet in figure 2). Undercutting of the slope during construction of highway in 1958 resulted in the sheeting joints daylighting in the rock slope (pole concentration is red dot on stereonet). The location of the 2008 rockfall is known as Porteau Bluffs, they run for just under 1 km along Howe Sound (49 33 52.15N; 123 14 01.44W), and the rock slopes along this section of highway exhibit similar rock mass characteristics to those involved in the July 2008 event."

Frank Baumann has kindly also provided a couple of other images of another landslide at the north end on Highway 99 - this time an incipient failure (Figs 3 and 4). It clearly shows that there are other potential problems on this road - although it is also important to stress that, surprising though this might seem, cracks like this do not mean that collapse is imminent or even likely.

Fig 3: Photograph (copyright Frank Baumann) of an ongoing failure on Highway 99 in Canada

Fig 4: Photograph (copyright Frank Baumann) of an ongoing failure on Highway 99 in Canada

Thanks to Frank, Steve and Keith for their contributions to this - I very much appreciate their input.

Rockslide on the Sea to Sky Highway in British Columbia

Hat tip to Scott McDougall, Erik Eberhardt and Andrew Giles, all from Canada, for this one.

Many readers will be familiar with the classic book "Rock Slope Engineering" by Evert Hoek, which still represents the bible for understanding the mechanisms of failure of hard rock slopes. The cover of the original version featured a photograph of a 1965 rock slope failure on the so-called "Sea to Sky" highway in British Columbia, western Canada:

This highway is the subject of some scrutiny at present as it represents the main transportation link between Vancouver and Whistler, which in 2010 will be hosting the Winter Olympics. The road, which has a history of being landslide prone, is currently undergoing a US$780 million upgrade. In Canada the national, and indeed now the international, press are quite exercised by a failure that occurred on this same road on the night of 29th July. Intriguingly, as Erik Eberhardt has pointed out, this rockslope failure occurred directly next to the 1965 failure featured on the cover of Evert Hoek's book:

Photograph, courtesy of Erik Eberhardt of the University of British Columbia, of the rockslide on the Sea to Sky highway. Used with permission.

This failure, which has a reported volume of about 16,000 cubic metres, has completely blocked the road and the railway. It appears to have occurred on a set of pre-existing and somewhat unfavourable joints:

Photograph, courtesy of Erik Eberhardt of the University of British Columbia, of the debris pile left by the rockslide on the Sea to Sky highway. Used with permission.

The scale of the landslide can be judged from this Reuters image taken from a helicopter. Note the workers on the debris - some of the blocks are rather large:

Xinhua / Reuters image of the landslide debris. Note the block sizes compared with the workers.

The inevitable media jamboree appears to be focused on two elements:
1. At the time of the landslide there was a bus passing by that was fortunately not buried but was hit by some of the debris. This has given the media the opportunity to run the traditional story line of a narrow escape. This from the Toronto Star (who incidentally have a great image of the slide taken from a helicopter, plus a video):

Peter Skeels's bus was lumbering up the highway that winds through British Columbia's breathtaking coastal mountains when he heard a roar that sounded like violent hail. He drove through and it wasn't until a few minutes later, when Skeels pulled over and saw the bus covered in dents and its windows shattered, that he realized a massive pile of rocks and boulders had rained down onto the road. "There was suddenly an unbelievable noise. It sounded like a hailstorm – you didn't really know what to make of it," said Skeels.

2. The inevitable concerns regarding access to the Olympic Games should such an event occur at the wrong moment. So, for example, Vancouver 24 Hours have run this:

Does VANOC have a backup plan to get spectators to and from Whistler venues if a rockslide closes the Sea-to-Sky Highway during the 2010 Winter Olympics? 24 hours requested an interview yesterday with VANOC vice-president of services and transportation Irene Kerr but instead received prepared statements via e-mail. The responses credited to Kerr said VANOC was deferring comment to the Ministry of Transportation.

"Where is the contingency plan? What would they do in the event of a major accident or a landslide as we see here today?" said B.C. NDP Olympics critic Harry Bains. "When we are inviting the world, we need to assure them that they will be able to watch the Games, that they will not be stuck on some highway for hours."

In the meantime, the clearance crews are working hard to deal with the debris and the obviously unstable portions of the cliff. CBC News has posted this terrific sequence of images of an unstable block being blasted. This is accompanied by an impressively sensible analysis of the situation on the ground.

Update: The Vancouver Sun has printed some rather interesting statistics about the hazards of this highway:

• "Prior to the improvement project the stretch of highway between Vancouver and Whistler averaged 405 rock falls, slides and debris torrents of varying size and severity each year"
• "Since 1906, at least 50 people have been killed in more than 13 debris torrents, 16 floods and two events of unknown cause that have been recorded on 13 of the 23 creeks along the route."

Notable events have included:

• "Oct. 28, 1921: A heavy Lower Mainland rainstorm triggered a washout that killed 37, injured 15 and flattened 50 houses at Britannia Beach.

• March, 1964: Six motorists and passengers missed death by seconds when tonnes of granite thundered on to the highway.

• Aug. 25, 1976: A rockslide near Lions Bay knocked the engine of a BC Rail freight train off the tracks and buried 30 metres of road under seven metres of rock and mud

• Oct. 28, 1981: Sixty years to the day since the Britannia Beach tragedy, nine people were killed as heavy rains brought down debris that knocked out a bridge at M Creek. Unsuspecting motorists drove over the ripped edge of the bridge into the raging creek below.

• Dec. 4, 1981: One person was swept away and drowned when a debris torrent buried a concrete bridge at Strachan Creek.

• Feb. 11, 1983: Two teenaged brothers were killed when Alberta Creek, flooded with rain, overturned a small trailer in which they slept and buried it under mud and debris at Lions Bay. A highway bridge and three houses were destroyed."

The Frank Landslide, 29th April 1903

As today is the 105th anniversary of the Frank Landslide in Canada, it seems appropriate to revisit this most interesting event. The town of Frank is located at about 49 degrees 35 minutes North and 114 degrees 24 minutes West at an elevation of about 1300 m in Alberta, Canada. The town on the back of coal deposits at the foot of Turtle Mountain to the west of the town (Figure 1). These were exploited by coal mines at the foot of the hill.

Figure 1: Google Earth image of the Frank landslide, Turtle Mountain, Alberta, Canada.

The landslide is fairly easy to see on Figure 1. The first signs of problems came in the weeks leading up to the collapse, when the coal tunnels started to show signs of movement. The final collapse occurred at 4:10 am when a block of about 650 m in height, 900 m in width and with a maximum thickness of about 150 m thick broke off the hillside and thundered into the valley below. The failure, which had an estimated volume of 30 million cubic metres, apparently took about 100 seconds, killing 76 people. Most of the victims were killed in their beds and their bodies could not be recovered as they were buried to a depth of about 30 m. Figure 2, from Natural Resources Canada, captures the scale of the event quite well. The landslide deposit extended over about 3 sq km, blocking the river and flooding about 2 km of the railway line. Seventeen coal miners were buried in the coal mine by the landslide but were able to dig themselves out over a 14 hour period.

Figure 2: Natural Resources Canada photograph of the Frank landslide, Turtle Mountain, Alberta, Canada.

The Frank landslide remains of great interest for a number of reasons:

1. There has been considerable controversy over the cause of the landslide. Initially the blame was pinned squarely on the mining activities, but more recently it has been increasingly accepted that in fact the geological structure, which was unfavourable for stability, was probably the primary cause. The mining probably did not help, and other factors such as rainfall may have also had a role.
2. There has also been a great deal of speculation over the the rate at which the landslide debris spread itself over such a large area. This very rapid runout behaviour is a somewhat enigmatic process in many large rockslides. Theories have abounded over the role of air entrainment, reduced basal friction, etc. The jury is still out - this remains one of the great questions in landslide science.
3. Parts of the mountain are probably still potentially unstable. In 1911 part of the town was relocated over fears about the stability of the slope. Today, real time monitoring is undertaken by the Alberta Geological Survey using a wide range of sensors. The aim is not to prevent a failure event but to provide a warning that it might occur. This is fine for a progressive failure or for one triggered by rainfall, but it offers little if there should be a large earthquake. Nonetheless, this is important work that is undertaken to a world leading standard. The work is described exceptionally well here