This blog provides a commentary on landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings. The blog is written on a personal basis by Dave Petley, who is the Wilson Professor of Hazard and Risk in the Department of Geography at Durham University in the United Kingdom.

This blog is a personal project that does not seek to represent Durham University.

Thursday, 27 March 2008

UPDATE 3 (1st April 2008): Landslide in Alesund, Norway

Over the last thirty years or so there have been a series of nasty landslides under apartment blocks on the edge of cities. Examples that spring to mind include:

1972: Po Shan Road, Hong Kong - 67 fataltities
1993: Highland Towers, Kuala Lumpur, Malaysia: 48 fatalties
1997: Lincoln Mansions, Hsichih, Taiwan: 28 fataltites

On 26th March 2008 there was an interesting landslide in the picturesque town of Alesund in Norway, once again on a slope under an apartment block. The slide is well captured in this EPA image:

EPA Image of the landslide in Alesund, from the Monsters and Critics website

The impact on the apartment block is evidently devastating, as this image shows:

EPA Image of the aftermath of the landslide in Alesund, from the Monsters and Critics website

According to reports, the landslide has moved the building forward by about 6 metres, triggering collapse of the bottom two floors. About 20 people were in the building at the time, of which 15 escaped by five are believed to be buried in the rubble. Given the collapse of the lower floors and a propane tank fire, which was still burning 24 hours later, their chances of survival are negligible .

The timing of the landslide is interesting as there was no significant rain recorded. This is however the snow melt season, so perhaps the slide was triggered by this. The presence of that large hillock behind is slightly intriguing. I would be very interested to see what stabilisation measures were in place on the steep slope above the apartments. Unfortunately the Google Earth imagery is too low resolution to see.

This type of slide does illustrate the hazards of building on sloping ground on the edge of urban areas, something that humans are doing increasingly often. If catastrophic landslides like this can occur in a country with a high level of regulation and expertise, such as Norway, the hazards in less developed countries should be clear.

Update:
Aftenposten has an interesting article on, and a revealing of, the landslide here. This picture is this one:

Aftenposten image of the aftermath of the landslide in Alesund, taken from the air

The image shows that the slope was indeed very steep and that the building has indeed been pushed forward. The article indicates that a row is breaking out over who is to blame:

"Speculation over the cause of the landslide continued to rage. One geologist said he'd warned that the hill behind the building, completed just four years ago, could give way. Others, however, said it had been secured and the building's developer and contractor claimed all regulations and re-enforcement measures had been followed. City officials had issued building permits after approving plans submitted."

I would suggest that there is a clear need for a genuinely independent investigation of this event, with an emphasis being placed not on blame but on learning the lessons in order to prevent future accidents like this.

Update 2: 28th March
Aftenposten has a second article about this slide here. A few issues emerge:
1. The land owners upslope from the landslide are now understandably concerned for their safety
2. Apparently "Parts of [the hillside] had been blasted away six years ago to make room for the building at Fjelltunvegen 31, and questions are being raised over whether that weakened the ground and contributed to the landslide." I am not sure that the blasting would have weakened the ground, but it was certainly have been over-steepened.
3.
"The blasting experts, developers and builders of the complex all have been quick to contend that they followed all rules and regulations for such projects, which are common in Norway. They also point out that they had reinforced the hillside behind Fjelltunvegen 31 with as many as 123 bolts." So it appears that rockbolts had been used to stabilise the slope. Given the size of the failure, I wonder how long they were? There is certainly no evidence of pulled out rock bolts on the photo, which suggests that they didn't reach the surface that failed. The first picture above shows that sliding has occurred on a remarkably planar surface - this is surely a pre-existing discontinuity?

Update 3: 1st April 2008
Aftenposten has now published another image of this landslide:

Aftenposten image of the aftermath of the landslide in Alesund showing the material and the block

This picture is very helpful as it shows that:
  1. The landslide has occurred in bedrock;
  2. The failure has occurred on a pre-existing joint that is inclined towards the building;
  3. The joint surface appears to have either weathered material or gouge on it. The strength of this is certainly much less than that of the intact rock mass;
  4. The lateral boundary of the slide is another joint;
  5. There is little evidence of the rock bolts on the joint surface




Monday, 17 March 2008

A nasty landslide in India

News reports from India this evening suggest that there has been a very nasty landslide in Himachal Pradesh. The Indian newspaper The Tribune reports that:
"At least six persons were killed and eight injured when a huge rock rolled down from the Nehru Kund hill on the Manali-Rohtang highway, about 5 km from here, this evening. The death toll could be higher as the debris brought down by the slide was spread over a large area."
and
"According to eyewitnesses, the hillock came down with thunder, which rattled the doors and windows of buildings, located far away...Rescue operations were on to retrieve the vehicles and any other victims buried. The sub-divisional magistrate Vinay Singh, assisted by a team of police, was supervising the operations. Rescue operations were hampered due to the darkness, though search light had been being used to continue search for victims...The famous Nehru Kund water spring was buried along with the temple. Local people informed that some tourists might also have been buried under the debris. Hundreds of vehicles, mostly of the tourists who were away towards Rohtang for sight seeing, were stranded as the landslide blocked the road.

Unfortunately Nehru Kund is a popular tourist destination, as this description on Maps of India shows:
One of the many exciting Manali Tourist Attractions, the Nehru Kund is only a 6 km journey from the heart of the Manali Town towards Keylong. The Nehru Kund is actually a spring which was named after the first prime minister of India - Late Pundit Jawaharlal Nehru. The serenity of the place will please any mortal on earth. The respected prime minister loved visiting the place and drink the crystal clear water from the spring when he used to stay in Manali. The graceful clean water spring is said to have its source at the Bhrigu Lake. The sound of the bubbling water amidst the peaceful silence of the place will play like music to your ears. The Nehru Kund is conveniently located on the National Highway on the way to Leh. It has emerged as a must visit for the tourists in Manali.

I fear that the deathtoll in this event could be rather higher than six.

Sunday, 16 March 2008

The Ecuador oil pipeline landslide

This is a good time to review the impact of the recent landslide in Ecuador that affected the lives of all of us. Once again, there appears to have been little recognition that a landslide was the cause.

The landslide in question occurred on 28th May in Amazonia as a result of heavy rain. Such landslides are not uncommon, but the significance of this one is that it severed 80 m of the Sote oil pipeline, through which the state oil company Petroecuador exports about 400,000 barrels of oil per day. The following day the Ecuador government declared force majeure. The impact of this was to push up global oil prices, which reached a record $103.05 per barrel on 29th February.

Fortunately, the pipeline was quickly restored and oil started to flow again on 4th March, when the Force Majeur was lifted. However, the legacy of this landslide is set to continue. Canada.com reports that Petroecuador has stated that the damage to the environment caused by the leak could take a year to clean up. About 4,000 barrels of oil were spilled, into the swamps of the Coca River. Although Petroecuador has said c.30% of the spill was recovered, the rest will need to be dealt with.

I do wonder sometimes why it is that the oil companies, whith some notable exceptions, don't invest more in good quality landslide assessment for pipelines. The costs of this must be tiny compared with the potential losses from a breakage and spillage.

Sunday, 9 March 2008

Strange landslide in the UK

Farmers Weekly Interactive carries a rather strange report and some excellent photos of a landslide that occurred near to Widnes in NW England on 29th February:

"Tractor Driver James Fletcher who works for Chester-based contractor Mike Harley, had a lucky esacpe when the field he was ploughing gave way beneath him. He was on the final run of a sloping field near Alvaney, Widnes, when the bank he was on collapsed, sending an estimated 15,000 tonnes of soil sliding down the slope. Mr Fletcher's tractor and plough was carried a quarter of a mile, through 360 degrees, crossing two fields and ended up being half buried in soil. Amazingly, the tractor started again once dug out, but had to be taken away on a low-loader."

IC Cheshire Online carries a rather more detailed report:

A wave of mud and rocks carried a tractor through three fields with its driver trapped helplessly inside. James Fletcher was ploughing a potato field at Teuthill Farm, Alvanley, at around 12.30pm last Friday when the ground gave way around him. He was trapped at the wheel as his tractor was dragged on its side through three fields and only escaped when the tractor hit two trees, smashing the windows so he could jump free. James, 45, of Bates Lane, Helsby, said: “I got there at about 9am and this was my last run up the field. “The next thing I knew, I was still moving forward but I was going backwards as well. The tractor was still ploughing and I just thought I was getting stuck. “Then the ground opened up and spun the tractor around. It smashed me into an oak tree which knocked the tractor over onto its side.“I was trying to open the door but it was too high above me. I was frightened to death.“I hit another oak tree on the other side which righted the tractor.“At the last minute I saw the house and I thought: ‘It’s time to get off now’. “If I hadn’t got out that would have been it.”

From what one can work out, the key facts are:

  1. The landslide was triggered by a tractor with a large plough;
  2. About 15,000 tonnes of material failed, travelling for about 500 m down a fairly gentle slope;
  3. The rate of motion was sufficiently fast to prevent the driver from escaping (the driver was very lucky by the way - if the tractor had rolled completely over, rather than righting itself, he might well have been killed.
This landslide is intriguing because of its exceptional mobility and speed of motion. In many ways it appears to be similar to a quick clay failure, but this is unlikely. Data from an amateur weather station at nearby Widnes suggests that there was not an exceptional of rainfall that day (2 mm), or indeed for the preceding few days. Thus, the nature and cause of this landslide is somewhat perplexing.

I am trying to find out more about it.



Friday, 7 March 2008

February 2008 landslide map

The map below shows the distribution of fatal landslides for February 2008.

The statistics are:
Number of fatal landslides: 24
Number of fatalities: 85

Thus February was well below the average for 2003-2007, which is 336 fatalities per annum. Note thiat this figure is skewed somewhat by the impact of the 2006 Leyte landslide. Without this event the average is 113 fatalities, suggesting that 2008 was a below avaerage year. Given the comparatively cold global temperatures (probably associated with La Nina), which implies relatively low levels of atmospheric energy, this is perhaps unsurpising.

February 2008 fatal landslide locations

The 2008 map to date is as follows:

2008 fatal landslide locations for January and February

There are a couple of things to note here:
1. The cluster that occurs along the southern edge of the Himalayas is not evident as yet. January and February are dry and cold [eriods in this region. There is usually a wet phase in March, so this should start to appear next month
2. The clusters in the Philippines and Java are now evident. The philippines is particularly badly affected this year - is this the effect of La Nina?

I would welcome any comments or questions.