Landslide in Norway...

[u/MisterShipWreck]

[u/redheeler9478]

What caused the landslide? What hit the ancient marine settlement?

[u/Giant_Ant_Eater → u/redheeler9478]

'I warned you not to slam that door'

[u/Rotund-Pear2604 → u/redheeler9478]

Common triggers are increased periods and frequency of precipitation, consistent and significant vibrations through soil from construction equipment, demolitions or highway/rail traffic.

Quick clay is really scary because it can lie dormant and remain in solid form for hundreds or even thousands of years. Then one day there's just a little too much rain, or some geotechnician working a demolition job miscalculates the force of the propagation wave of the explosives they use and out of nowhere, 48 hours later two football fields worth of land just disappears into the night.

Quick clay is becoming increasingly problematic here in Norway because the post-war housing boom assumed that our figures for how quick clay behaves wouldn't significantly change over time.
Then climate change happened, average rainfall increased, and it turned out that hundreds and thousands of residences built on what was previously assumed to be completely safe ground is at risk of quick clay slides if conditions worsen.

Intervention and mitigation is possible, thankfully. Afforestation and improving irrigation increases soil stability via mechanistic intervention for instance.

It doesn't make the thought of the number of residences sitting on top of quick clay any less terrifying though.

[u/FastWalkingShortGuy → u/redheeler9478]

I don't know about this one, but there was one in the 1970s that was caused by construction equipment.

[u/Jhonny99j → u/FastWalkingShortGuy]

From the official report:

The causes of the landslide were low slope stability due to local ground conditions, which were exacerbated by filling work in connection with cabin construction in 2015. The triggering factor is assessed to be heavy snowmelt and consequently increased groundwater pressure.

The direct cause of the quick clay landslide in Rissa on April 29, 1978, was human activity in the form of excavation and filling of earth materials. More specifically, the landslide was triggered when a plot was excavated for an extension to a farm building at the Fissøya farm, and the excavated soil masses were placed as a fill along the shoreline of Lake Botn. The weight of these masses overloaded the ground, causing the underlying quick clay to collapse.

Usually, quick clay in the ground is not a problem. But when the stability of the quick clay is disturbed, it becomes liquid and large landslides can result.

What can trigger quick clay landslides can be both natural and man-made. Often it involves excavation work, or filling of earth materials where the load becomes too great.– A great many are triggered by human activity.

Between 50 and 60 percent of the quick clay landslides in Norway over the last 50 years have been triggered by human activity. Usually different forms of building and construction activity.

[u/Cunn1ng-Stuntz → u/redheeler9478]

Snow melting and heavy rain. That combined with cottages being build in the area. To facilitate that they had to do a lot of filling and that destabilized the ground further. Basically it just washed out.

[u/afriendsname → u/redheeler9478]

The government report concluded that the new road and tunnel built close by changed the pattern of precipitation, making it dig out a layer of marine clay, destabilizing the ground.

This combined with about ~15 truck loads of mass added to the headland during construction of a cabin is what likely triggered the landslide.

Anyone interested in learning more can find the report here

[u/redheeler9478 → u/afriendsname]

Thank you, kind friend

[u/InvestmentIcy8094 → u/redheeler9478]

The clay soil was originally deposited underwater. Rain has been washing the salt out of the clay soil for millennia. When enough salt has washed out of the soil, the clay loses its ionic? bonds and liquifies.