Kettle holes - witnesses of the last ice age
Basic information about the last glacial period can be found in this blogpost.
A characteristic element of the post glacial landscape are the so-called kettle holes, which were formed at the end of the last glacial period.
Active glaciers are in a sense alive because the glacial ice generally is in motion. During the last glaciation of Scandinavia, the entire subcontinent was covered by ice masses of about 2,000 meters thickness. At the end of the last ice age, a little more than 10,000 years ago, the ice began to melt and with it began the retreat of the continental ice sheets towards the north. At the southern end, more or less large blocks of ice broke off during this process, remaining in the open landscape until they’ve finally melted as well.
Such blocks, separated from the active glacier, are called dead ice because they are no longer in motion and remain in place until they've completely melted. Depending on the size of the dead ice block, however, melting can take up to several decades. Meanwhile, sediments, transported by the meltwaters of the retreating glacier, are deposited around and on top of the ice block and may even cover it fully. This slows down the melting process even further. Eventually, the melting of the dead ice block leads to the subsidence of the deposited material and a so-called dead ice hole or kettle hole is formed.
Since dead ice holes are formed by the influence of both glacial ice and meltwater, they are scientifically called glaciofluvial or fluvioglacial landforms. Hereby the terms glacial (created during the last ice age) and fluvial (created by flowing water) are combined.
Today, many kettle holes are water-filled and have thus developed into kettle lakes. In Sörmland, however, there are several dead ice holes that are not filled with water. These are often located in forest areas and it takes attention and the necessary background knowledge to discover them. Here and there, however, you will find an information board that will enlighten even the layman about these geomorphological forms and their origin.
An easily accessible dead ice hole is located along section 15 of the long-distance hiking trail Sörmlandsleden. I offer a 9.5 km guided hiking tour, with Skottvång as the starting point. On this hike, I not only tell about the kettle hole but as well about other directly visible landscape forms and characteristic animal species in the ecosystem of the three Marvikarna lakes, which is a protected nature reserve.
For more information and guided tours, please contact me directly.
(title image: kettle hole; Tiia Monto; CC BY-SA 4.0)
Post sources:
- Kettle (landform) Wikipedia: https://en.wikipedia.org/wiki/Kettle_(landform)
- Lexikon der Geowissenschaften: https://www.spektrum.de/lexikon/geowissenschaften/fluvioglazial/5093
- Dead ice Wikipedia: https://en.wikipedia.org/wiki/Dead-ice
- Toteis Wikipedia: https://de.wikipedia.org/wiki/Toteis
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