Enormous icebergs have scraped along the bottom, and made deep furrows.

Around 10 - 15.000 years ago, towards the end of the last Ice Age, mainland Norway was covered by a kilometre-thick ice sheet. Enormous icebersg calved from the glaciers, like we see in Antarctica today. Some of these icebergs were so huge that they scraped the seabed, when they drifted with currents and wind. These iceberg ploughmarks may be several kilometres long, over 100 m wide, and 10 - 15 m deep.