The Geological Wall is a geological monument in the Belgian municipality of As. The wall is about nine meters high and was created by gravel extraction. The wall is located in the former Groeve Hermans, part of the Hoge Kempen National Park, close to the entrance gate to Station As.
The wall is the first geological monument in Flanders and was recognized as a protected landscape in 1994. The wall shows about 900 000 years of geological history. The quarry wall consists of several packs where one pack is composed of a layer of coarse gravel at the base, which becomes finer towards the top, transitioning into a sand layer and in some cases even a clay layer. On top of the clay layer a new layer starts with coarse gravel at the base and then fine gravel, sand, silt and even clay.
This accumulation is the result of fluvial deposits in the middle Pleistocene, between 850,000 and 130,000 years ago. The flow rate of and the ensuing energy determined whether coarse or very fine material is present in the deposited package. This is typical of a braided river: small beds that cross each other and deposit different sediments, depending on place and time.
This river is the Meuse, now a rain river, but during the deposition period the flow increased enormously after the long winter period due to masses of snow melt water from the Ardennes. In 2021, the Maas will be 15 km further east and 56 m lower.
The orientation of the wall follows the longitudinal profile of the channel, which slopes down from the south to the north. The oblique stratification is visible in the finer sediment as well as in the gravel layers. The flattened gravels lie overlapping each other, which is also an indication of the direction of the current.
Source: Wikipedia