Quick clay
Quick clay is a special type of marine clay that can lose its structure and turn almost liquid if it is overloaded or disturbed. You can build on ground with quick clay, but it requires thorough geotechnical surveys and often costly measures. Awareness has increased sharply since the Gjerdrum landslide in 2020, and the authorities have tightened the requirements for mapping and documentation since then.
Mineralogically, quick clay is a fine-grained clay deposited on the sea floor after the last ice age. The salt ions in the pore water bound the mineral particles together in a stable card-house structure. When the land rose and the areas came above sea level, fresh water gradually washed out the salt, and the structure became vulnerable. Loading, changes to the terrain or erosion along a stream can trigger a collapse where the clay behaves like a liquid and can move several kilometres in minutes. The deposits follow areas below the marine limit, and in Norway they are especially widespread in Østlandet, in Trøndelag and parts of Nord-Norge.
Events such as the Verdal landslide in 1893, the Rissa landslide in 1978 and the Gjerdrum landslide in 2020 have each time tightened the requirements for mapping and control. The current methodology is set out in NVE's guide 1/2019 on quick clay and area stability, and awareness maps and hazard zones are published by NVE on Geonorge. NGU manages the datasets for the marine limit and superficial deposits in parallel. The Planning and Building Act, section 28-1 requires the building ground to have sufficient safety against hazards, and TEK17 section 7-3 "Safety against landslides" sets this out in detail for quick clay and other landslide types. The section divides buildings into safety classes (S1-S3) with matching requirements for hazard probability and geotechnical safety factor, and the guidance to section 7-3 refers directly to NVE's methodology for assessing area stability. In practice, this means that a quick clay hazard zone triggers a requirement for a geotechnical expert assessment before a zoning plan, framework permit or construction start permit can be granted.
In the early acquisition phase, it is worth checking several sources at the same time: NVE's awareness maps for quick clay, existing ground surveys in NADAG (the national database for ground surveys, held by NGU), and the municipality's zoning provisions. A hazard zone is not a building ban zone, but the cost picture for foundations and area stabilisation measures (piling, soil replacement, drainage, counterfill) can change the project economics significantly.
In Placepoint, NVE's awareness maps and known hazard zones for quick clay are shown as a risk map layer over the map, and you can find known ground surveys in the geology map layer.
How the dataset appears in the map
The dataset is part of the map layer Geology as Quick clay:
From Placepoint's glossary: Quick clay
More information: NVE: quick clay landslides, NGU: marine limit, Store norske leksikon: kvikkleire
English: Quick clay (sensitive marine clay prone to landslides).
Frequently asked questions
What is quick clay?
Quick clay is a special type of marine clay that can collapse and turn almost liquid if it is overloaded or if the water content changes. It represents a significant geotechnical risk and is especially widespread in Norway and Scandinavia.
Can you build on ground with quick clay?
It is possible to build on ground with quick clay, but it requires thorough geotechnical surveys and often costly ground reinforcement measures. The scope of the measures depends on the stability assessment for the area.
How do I know whether there is quick clay on a site?
You can check NVE's awareness maps for quick clay at nve.no, or use Placepoint, which shows geotechnical hazard maps directly in the map interface. A reliable assessment always requires geotechnical ground surveys on site.
What happened in Gjerdrum, and what does it mean for developers?
The quick clay landslide in Gjerdrum in 2020 sharply increased awareness of quick clay risk. The authorities have since tightened the requirements for mapping and risk assessment for development in quick clay areas.
What does it cost to secure a site against quick clay?
Costs vary enormously depending on the ground conditions and the scope of the measures. Anything from drainage and soil replacement to pile foundations may be relevant, and prices can range from a few hundred thousand to many millions of kroner.