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Researchers have mapped 10,000 years of avalanche history

At the bottom of a small lake in Norway, 10,000 years of avalanche history lies buried. Researchers have now mapped how many avalanches have occurred.

Johannes Hardeng has studied avalanches.

(Photo: Private)

Tori Pedersen Tori Pedersen Tori Pedersen Communications Adviser

Presented by: Presented by: Presented by: University of Bergen

Published 1 April 2026 - 00:01

How does climate change affect avalanche activity?

The answer lies 541 metres above the Hardanger Fjord. Not far from the glacier Folgefonna lies a lake called Vatnasetvatnet. Along one shore, the terrain rises steeply towards the mountain Vasslifjellet.

For 10,000 years, avalanches from this mountainside have transported loose particles such as sand, clay, and gravel out into the lake.

“By driving long plastic tubes into the bottom of the lake, researchers can extract layer upon layer of what at first glance looks like mud. But these metres of sediment tell a rich story about what has happened far back in time,” says Johannes Hardeng.

He is a former researcher at the University of Bergen who now works at the University of Oslo.

These sediment cores were the starting point for the research project.

A natural archive

The work builds on a master's thesis from 2009. That was when the first sediment cores were brought up.

In 2022, the researchers collected new sediment cores and used new methods to analyse the sediments.

Vatnasetvatnet in Hardanger. The photo was taken during field mapping around the lake in autumn 2022.

Here we see an avalanche that ran out into Vatnasetvatnet during winter.

On the way to Vatnasetvatnet in 2022 to retrieve sediment cores.

“The processes active around a lake shape the sediments that accumulate on the bottom. In this way, lakes function as natural archives where information about the past is preserved. Vatnasetvatnet is well suited for reconstructing past snow avalanches because the lake is isolated. It's not part of a large, complex river system and is therefore barely influenced by other processes than avalanches,” says Hardeng.

Mapping the area

To ensure that the water has not been influenced by other processes, Hardeng mapped the area around the lake. He lived up by the lake for about a week and carried out the necessary investigations.

This was to rule out that anything other than avalanches could have affected the sediments on the bottom of the lake.

By using dating methods, the researchers could determine that the the lowest layers in the sediment core were 10,000 years old. The lake formed when the ice retreated from the area after the last ice age, exactly 10,000 years ago.

Therefore, the researchers were confident that the sediment cores captured the lake’s entire history.

“This means we have a continuous history going 10,000 years”, Hardeng says.

A small coffee break during a mapping trip. The Alaskan husky Rago is enjoying the view.

This is how terrain mapping is carried out. The photo was taken on a different trip.

Various techniques were used

With the naked eye, the researchers could see that the otherwise dark, muddy material in the sediment core was interrupted by thin, lighter layers. The lighter colours are made of silt, sand, and gravel that has been transported into the lake by avalanches.

The researchers carried out a series of sediment analyses. Among these were high-resolution CT images and XRF scanning. XRF is a rapid analysis method used to determine the chemical composition of materials. They then found many more layers that were not visible to the naked eye. The researchers counted a total of 187 such avalanche layers.

“There have probably been a lot more avalanches than 187, but they must be big enough to reach the lake and leave remains,” explains Hardeng.

Important research

The methods used makes it possible to create a unique avalanche archive for the western part of Norway.

“It's the longest and most detailed record of its kind from the region. The work clearly shows how climate, storm activity, and winter conditions have varied throughout the entire Holocene, and how such changes have influenced the frequency of avalanches in steep mountain terrain,” says Jostein Bakke.

He is a professor at the University of Bergen and the Bjerknes Centre for Climate Research.

Bakke runs a research centre at the university that focuses on how the Scandinavian mountain environments respond to and interact with accelerated global climate change and increased human impacts.

He explains that this research demonstrates how natural archives in these mountain regions can provide knowledge that is directly relevant to today’s and future societal challenges – particularly those related to climate change and natural hazards in mountain landscapes.

“Hardeng’s work shows how crucial it is to understand the long-term development of mountain environments, and how these systems evolve and respond to climate over thousands of years,” says Bakke.

Map with data — 3D terrain model of the Vatnasetvatnet catchment (south-facing perspective), showing mapped avalanche tracks (1 and 2) and coring locations. The avalanche tracks are divided into accumulation and trigger zones (red) and colluvial fans in the runout zones. Elevation data from here imagery overlay from here.

Core sample segments laid out on a lab bench with tools and measurement scales — This is what the sediment core looks like when opened. You can see the layers as distinct bands.

Horizontal ice core segment with layered structure above a scale on black background — This is what the sediment core looks like on a CT scan.

High avalanche activity in recent times

The findings from the study show that the avalanche frequency is first and foremost controlled by winter ground temperatures and atmospheric circulation over the North Atlantic. Especially the North Atlantic Oscillation (NAO), which is a weather phenomenon caused by differences in atmospheric pressure between the Icelandic Low and the Azores High.

The researchers found that from 10,000 to 6,500 years ago, there were only 2 to 3 avalanche events. This was a period characterised by warm summers and cold, dry winters.

From 6,500 to 4,200 years ago, increasing winter precipitation and stronger westerly winds led to a marked rise in the number of snow avalanches.

However, the highest avalanche activity occurred from 4,200 years ago up to the present. During this time, there have been as many as 45 avalanches per 500 years. This coincides with the period when Norwegian glaciers expanded due to relatively cool summers and mild, precipitation‑rich winters.

"By understanding how climate change has affected the avalanche activity through thousands of years, we become better equipped to make good decisions in a changing climate", says Hardeng.

Reference:

Hardeng et al. 10 000 years of snow avalanche activity in western Norway: a multiproxy lake sediment record from Lake Vatnasetvatnet, Hardanger, Climate of the Past, 2026. DOI: 10.5194/cp-22-265-2026