Wijstgronden in de maashorst
The Maas once flowed through the primeval area. But due to a fracture in the earth’s crust, the ground rose more and more. This pushed the Maas to the east and the land became higher. That high piece of land is called a horst. Hence the name Maashorst. The lower area is called a slenk.
Nowadays you can no longer see the difference in height, but the ground still shows traces of the fault. On the horsten you can see gravel and sometimes large boulders. In the ice age these were deposited by the then still wide meandering Maas. The gullies can be recognized by fine cover sand.
On the west side of the primeval area lies one of the largest faults: the Peelrand fault. A fault that has been active since the Miocene that began approximately 23 million years ago. Along the Peelrand fault there are many wijgronden: high, marshy areas where the iron-rich groundwater rises as seepage. A rare phenomenon that only occurs under very specific circumstances and is nowhere in Europe as visible as here in De Maashorst.
Heigh and wet
The grounds are high and wet. A striking combination. How does that work?
It all starts at the Peelrandbreuk. This fault marks the transition between the Peelhorst and the lower Centrale Slenk. The high-lying horst consists of coarse-grained sand and gravel through which groundwater easily seeps. The low-lying slenk, on the other hand, consists of fine-grained, poorly permeable sand. Just like the slenk, the fault itself also forms a barrier for the groundwater.
If that water seeps down from the high side and encounters the fracture there, it can no longer go anywhere and moves as seepage water to the surface. Contrary to what you would expect, the high grounds are wet and the lower grounds remain dry. This rare form of seepage is called wijst.
is the fracture still visible?
Not really. That is because the upward moving horst has been worn away by the wind over time and the gully has been filled with sand and gravel. As a result, a large part of the subsidence has been removed. The original height difference of about two hundred meters has disappeared everywhere. Except at Uden. There, a height difference of about five meters is still visible. It is therefore the most visible remnant of the original steep slope. Special to see.
iron-rich water
Groundwater flowing towards the fault is rich in iron. When this water appears on the surface, it oxidizes. This gives the water its special rust-brown color. Beautiful to see!
more about the wijst
In the video below, Godert Verbeek, advisor at Waterschap Aa en Maas, tells more about the wijst and the Geopark. The images you see were recorded at the Annabos, the place in nature reserve De Maashorst where the wijst is clearly visible.
the natural highlights
De Maashorst is full of special nature