Marine limit
The marine limit is the highest level the sea reached after the last ice age, about 10,000 to 12,000 years ago. If you plan to buy or build, the limit matters because quick clay can only be found below it.
During the ice age, the ice pressed the land down. When the ice melted, the sea therefore stood higher up in the terrain than it does today. The land has risen since then, and it still rises by a few millimetres a year. Old shorelines, terraces and deltas from that time remain in the terrain. The level varies a great deal: close to zero in some places along the west coast, around 220 m above sea level in inner Østlandet (Romerike and the Mjøsa area) and around 175 m in the Trondheim area. The marine limit is a line in the terrain that follows the old shorelines, not a single height for the whole country.
Below the marine limit there may be sea and fjord deposits of marine clay and silt. When fresh water has washed the salt out of the pore water, the clay can become quick clay. Much of the clay below the limit is still firm and stable, so a location below the marine limit does not automatically mean quick clay. Above the marine limit, no marine clay has been deposited, and quick clay does not occur there. The marine limit is therefore the first filter in any quick clay assessment. If the site lies above the limit, you can rule out quick clay and move on to other topics.
The Geological Survey of Norway (NGU) manages the Marine border dataset and the derived Possibility of marine clay (MML) dataset. MML combines the marine limit with the map of loose masses and identifies areas where marine clay may be found. The Norwegian Water Resources and Energy Directorate (NVE) manages hazard zones and susceptibility maps for quick clay. TEK17 § 7-3 in the building technical regulations sets requirements for safety against landslides, and NVE guideline 1/2019 describes the method for assessing area stability.
A site below the marine limit with fine-grained loose masses usually triggers a requirement for a geotechnical assessment before a zoning plan or outline permission can be granted. Stabilising measures can bring significant costs and change the project's finances. Earlier ground investigations in NADAG often give a first picture of the ground. A site above the marine limit can still have other challenges, such as bog, landslide risk or a great depth to bedrock, but not quick clay. The limit therefore belongs early in any site analysis.
In Placepoint, the marine limit appears as a separate map layer under Geology, supplied via Geodata AS. You can turn it on together with Possibility of marine clay, Loose masses and Quick clay to see the full picture at once. Report: Risk and climate risk covers quick clay, from the marine limit to loose masses.
How the dataset appears in the map
The dataset is part of the map layer Geology as Marine border:
From Placepoint's dictionary: Marine limit
More information: NGU: how the marine limit and the possibility of marine clay map work, Store norske leksikon: marine limit, NVE: natural hazards, quick clay guideline 1/2019
English: Marine limit (highest postglacial sea level).
Frequently asked questions
What does marine limit mean?
The marine limit is the highest level the sea reached after the last ice age, about 10,000 to 12,000 years ago. The ice had pressed the land down, so the sea stood higher up in the terrain than it does today. The land has risen since then.
How high is the marine limit?
It varies from place to place. In some places along the west coast it is close to zero, in inner Østlandet it is around 220 m above sea level, and in the Trondheim area around 175 m. You therefore need to check the map for the specific site.
Can there be quick clay above the marine limit?
No. Above the marine limit, no marine clay has been deposited, so quick clay cannot form there either. The site can still have other ground challenges, such as bog, landslide risk or a great depth to bedrock.
Does a site below the marine limit mean there is quick clay there?
Not necessarily. There may be marine clay below the marine limit, but much of it is firm and stable. If the site has fine-grained loose masses, you should still expect a requirement for a geotechnical assessment before zoning or outline permission.