Drumlins generally consist of an accumulation of glacial debris – till – and are found in areas that were covered by ice sheet. As the ice advanced, it moved rocks, gravel and sand and created tear-shaped raised ridges running parallel with the movement of the ice.

“Until now, scientists have been divided on how drumlins were created,” says Mark Johnson from the Department of Earth Sciences at the University of Gothenburg. “Because they are formed under the ice, it’s not an observable process. Drumlins are common almost everywhere the Ice Age ice sheets existed, but they’re almost unknown with modern-day glaciers. Now, though, we’ve found a new drumlin field by the Múlajökull glacier on Iceland. It’s quite unique.”

The melting of glaciers as a result of climate change has helped the researchers to study this geological phenomenon. The drumlin discovery on Iceland has presented unique opportunities to study their structure.

“One of the drumlins we found was sliced through by erosion. This gave us an opportunity to study it layer by layer, and it was clear that it had been built up only recently. In other words, the glacier has not just retreated to reveal old drumlins, but is continuing to create new ones.”

There are currently multiple theories about the origins of drumlins. The Gothenburg researchers’ discovery shows that they can form within two kilometres of the edge of the ice.

“A surging glacier can move 100 metres a day, as opposed to the more normal 100 metres a year. If we can link drumlins to fast-moving glaciers, this would mean that the ice sheet advanced much more quickly than scientists currently believe.”

The link between drumlins and rapid ice movements is important for climate research. When modelling climate change, we need to know how high and how cold a glacier was in order to understand the last Ice Age. A glacier that moves quickly will not be as thick. This discovery could therefore affect how scientists approach climate modelling.

Solving the riddle of the drumlin is a longstanding dream for Mark Johnson:

“We discovered the drumlin field while flying in towards the edge of the glacier to do a completely different study. It was the most exciting thing I’ve been involved in during my research. All geologists know about drumlins, and when I began to study geology in Wisconsin in the 1980s, many people would come there to study the drumlins in the area. Coming up with a theory for how they formed was a big question even then.”

The discovery of the new drumlin field was made by Mark Johnson from the Department of Earth Sciences at the University of Gothenburg in collaboration with researchers from Iceland, Norway and the UK.

The study “Active drumlin field revealed at the margin of Múlajökull, Iceland: A surge-type glacier” was published in the journal Geology.

Where to find drumlins in Sweden:

Sandsjöbacka: The drumlin is clearly visible as a ridge to the side of the E6 highway south of the service station at Sandsjöbacka.
Latitude 57.54434, longitude 12.03921.

Dössebacka: The waterworks have been built on a drumlin – water from the Göta River is filtered through the drumlin’s sediment to become drinking water.
Latitude 57.91095, longitude 12.04391.

Äskhult: The old village and its farmland lie on top of a drumlin, as is clear on the map.
Latitude 57.42715, longitude 12.28311.

Drumlins are very common throughout Norrbotten in northern Sweden, especially in the triangle between Arvidsjaur, Luleå and Jokkmokk, and along Luleälven River and highway 97 northwest of Boden.
Latitude 65.98687, longitude 21.05763.

Drumlins are also an important part of the landscape in much of Småland in southern Sweden. For example, there are many drumlins parallel with the lakes south of Eksjö, and highway 40 passes over a drumlin between Nässjö and Eksjö.
Latitude 57.63379, longitude 14.89638.

Caption 1: The edge of the Múlajökull glacier on Iceland. The ridges between the lakes are drumlins. Photo: Ívar Örn Benediktsson.

Mark Johnson, Department of Earth Sciences, University of Gothenburg
+46 31 786 28 08