Dolmens are not the only special remains from the Ice Age: in Drenthe there are also hundreds of pingo ruins and exhalation bowls. These have been misunderstood so far, but pingo specialist Anja Verbers hopes to change that. Her book Pingo Ruins: special Ice Age relics in the landscape will be published next week.
“You won’t see it until you realize it,” says the foreword to the book. It is a well-known statement by Johan Cruyff, which can be applied well to the Pingo ruins. The small peat bogs and lakes are hardly noticeable as you pass by, but Verbers has mapped dozens of them.
The physical geographer conducted research into pingo ruins for Landschapsbeheer Drenthe for ten years. “A pingo ruin is, as the word suggests, a ruin of a pingo. That is an ice mound that was created during the last ice age, more than 15 to 20 thousand years ago,” she says in the Radio Drenthe program Cassata.
The groundwater under such an ice mound tried to rise beneath the frozen ground. This is how an ice lens was formed. It continued to grow until the lifted ground cracked open. This allowed sunlight to reach the surface and melted the ice. This created a depression filled with meltwater and later groundwater.
These so-called lows could be very large and deep. In Drenthe the deepest is about seventeen meters. Not all pingo ruins are still filled with water. For example, some pingo ruins slowly silted up with organic material and peat was formed.
Where the peat has been extracted, small lakes have sometimes been created. In other places where the peat has dried out, groves have emerged, but there are also dry pingo ruins. “That is unique in Drenthe. They only occur between Gieten and Emmen and there are about thirty of them.”
In addition to pingo ruins, Verbers has also examined many exhalation bowls. “They were blown out by the wind. During the last ice age it was extremely cold. There was almost no vegetation, but a lot of wind. When the wind blows over a sandy plain, it can form dunes, but also depressions.” The largest exhaust basin is located near Annen and has a diameter of one kilometer.
Verbers retired in mid-December and has bundled all her research into the ruins and bowls in a book. She not only leaves behind a pingo book, but also a pingo ruin in her name.
When Verbers retired, colleagues surprised her by naming a ruin Verbersveen. “They were so sweet and crazy to arrange that. I couldn’t believe it, I thought it was a joke.”