Category Archives: landslides

Landslides in Norway and the Forest of Bowland.

On 3rd June 2020 a remarkable landslide occured in Norway when a slice of land complete with houses slid into the sea. The poor owner videoed it and I hope he got something for that. Later you can read a geological blog on it and see the whole video. It is both awesome and sad. Fortunately there was no loss of life.

Here is the house almost entering the sea.

Alta quick clay landslide

I live on the edge of the Forest of Bowland which I explore on foot and bike. It is a fascinating area and luckily many drive past without stopping! As a result it is not very crowded. I often don’t meet a soul on a walk.

My favourite cycle ride is over the Trough of Bowland, through Whitewell and Chipping and thus back to Garstang. There are several variants and when I did it this May I covered 40 miles. When I do it clockwise I always stop by Smelt Hill having done the major climb. A few centuries ago lead ore from the limestone anticline at Sykes was smelted here. Just above the old smelting area there is a bend with convenient stones. Thus I stopped here in May for my lunch. I just love the view.

But look carefully, a few hundred yards upstream you can see a tongue from the left sticking out towards the river.

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This shows it more clearly and it is the debris from a landslip many thousands of years ago. I suggest about 20000 yrs.

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To summarise the geology the area is of Carboniferous strata , with Bowland Shales capped by Pendle Grit as in the cross-section below ( which is for the area at bit further on.).

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This blog of the section of Bowland Shales on Pendle hill gives more detail

https://michaelroberts4004.wordpress.com/2014/09/15/namurian-succession-upper-bowland-shales-to-pendle-grits-forest-of-bowland/

The shales are soft and the grit hard. If the shale gets totally wet, in the right conditions, it will slip and cause a landslip. There are many examples in the Forest of Bowland and are marked on the Geological Survey 1 :50000 map.

Another example is between Parlick and Saddle Fell where the area now marked as Wolf Fell has slipped off the saddle! You can see that to the right of Parlick which is on the left of this photo. In the shadow you can see a cwm, which almost appears glacial, but is not.  An area of 1km by 1/2 km has simply slipped downhill. It is marked on the geological map. It must have been a dramatic sight.

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The slope is most irregular. This is the hummocly terrain between Parlick and Saddle Fell.

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This photo taken last september is looking across the landslip from Saddle Fell to Parlick. You can see where it lsipped off Parlick. It must have been dramatic to watch.

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Another dramatic example is Blue Scar up the Dunsop Valley from Dunsop Bridge. There a l;arge area had slump from near the top of the hill leaving a cwm with steep sides. The hill is capped with Pendle Grit overlying Bowland Shale.

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If you could go back in time, when that cliff was not there there was instead a smooth hillside of mostly shales.  Geologically this is the contact between to Bowland Shales and the Pendle Grit. Below the Pendle Grit there are alternate shale and grit bands, with some visible in the lower part of the photo.

A few years ago I went that steep slope to look at some of the Hind Sandstone which was deformed most oddly soon after deposition. It was not the wisest place to do field geology and I do not recommend it!!

 

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This is the “headwall” of the landslip, which I visited the previous year .

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Here the shale and grit are melded together, presumably before they solidified. It was a difficult photo to take as it was very steep and one step back to get a better shot would have resulted in a rapid descent of 100ft. Howver this is the geology of 300 million years ago rather than of today.

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There are many examples of landslips marked of the Geological Survey maps of Garstang and Lancaster;

  • On the north side of Grize Dale valley below Nicky Nook
  • On the north side of Langdon Brook by Langdon Castle
  • On the slopes of Wardstone north of Tarnbrook

Most of these are south facing, which may indicate that it was warmed sufficiently to slide at the end of the Devensian Ice Age, and   most of them were triggered by the melting of permafrost after the last ice advance – & some of them are still unstable, as in the Trough of Bowland.

To visualise  the speed and devsatation of what happened think of the disaster at Aberfan.

There are more landslips if you check the maps but these are the clearest.

As well as that there are an increased number small landslips, as on the minor road by Walmsley bridge, which was clearly due to the heavy rain earlier this year. There are considerable numbers round the country both in high land (I found a cracker on Y Garn two years ago)  and also near the coast as on the Isle of Sheppey tipping houses over the edge. In a sense, this is inevitable due to the change in weather patterns. Since 1980ish British weather has seen both longer wet and dry periods, rather than more broken weather, which is ideal for landslips and building subsidence.

Sadly, we can expect more landslips, and possibly not only small ones but even as large as those ancient ones in the Forest of Bowland.

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I’ll now give an American example, which we visited briefly on holiday in the American West some years ago. We were staying  (in a grotty place) in the Grand Teton National Park and apart from going up to 10,000ft by cable car we explored the area and thus went to the landslide at Gros Ventre some miles to the east. It is one of the biggest recorded landslips.

The top of the of the mountain is about 9000ft , 2000ft higher than the base. When th mountain gave it slipped and ran up the other side of the valley for 300ft. This cause a dam which resulted in fatalities when it broke.

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And so we come to the dramatic footage from Norway, which should remind us how unstable our planet is.

 

The remarkable video of a landslide at Alta in Norway yesterday is probably the finest recording of a quick clay landslide to date.

Source: Alta: a truly remarkable video of a quick clay landslide in Norway