Today we're going to talk about a geological formation called a butte . These are formed by erosion and are usually found in flat areas. I consider them evidence of the passage of time, of the retreat and evolution of a slope or plateau. They have several characteristics worth knowing about, as they explain a bit about the dynamics of the Earth's crust.
In this article we are going to tell you what a witness hill is, its characteristics and how important it is for geology.
What is a witness hill
This is a geological formation resulting from soil erosion over many years. We are speaking on a geological timescale , so it cannot be evaluated on a human timescale. The butte reveals the evolution of a plateau or platform on a flat surface. This surface is formed by horizontal layers of soft and hard rocks where the constant wind has caused erosion that has modified the terrain.
Erosion occurs more frequently in the softer soil layers. Rivers cause erosion, forming hills and other landforms, as can be seen on the central plateau . If the plateau is eroded on all sides, it forms what are known as buttes. These buttes have occupied these locations for millions of years.
How it is formed
These geological formations are sculpted by erosion and are called buttes because they bear witness to the former extent of a horizontal platform that has become isolated. Differential erosion caused by rivers and ravines has resulted in alternating layers of harder and softer sedimentary rock. These buttes are defined by the erosional slope, characterized by a steeper section of hard rock and a gentler section of soft rock. The harder section is called the cornice, and the softer section is called the slope.
The witness hill has a convex-concave profile and varies depending on the resistance provided by the hard and soft rock layers. When erosion by rivers increases, the witness hill appears flat on all sides. Therefore, they are evidence of a platform that existed in that same place millions of years ago. The remaining relief is a set of hard and soft layers arranged horizontally, which erosion may have sculpted.
Where are the witness hills
They are quite common in the sedimentary basins of the different rivers. These formations can be found in the Pilot mountain, in North Carolina, in the Cerro de la Teta (Guajira Peninsula) and in the Dori plateau (Burquina Faso). In our country we can also find it in different tabular reliefs such as the Ebro river depression and in the sedimentary basins of the central plateau. In Madrid we have the Cerros de la Marañosa, in the Cerro de los Ángeles and the Buenavista, and in the province of Palencia, the Cerro del Otero.
We will describe the characteristics of Cerro de los Ángeles (Hill of the Angels). It is located approximately 10 kilometers from Madrid, in the municipality of Getafe. It has been considered the geographical center of the Iberian Peninsula. Therefore, it holds great importance despite the lack of scientific measurement to confirm this. On the esplanade at the summit of this hill stands the well-known hermitage of Our Lady of the Apostles. Dating back to the 14th century, it is a remarkably well-preserved monument.
On the slopes of this hill are holm oak pines, playgrounds, a soccer field, trails, and a picnic area. This has made Cerro de los Ángeles a pleasant tourist attraction in close contact with nature. Its base is 610 meters high and it reaches a height of 666 meters. At its highest point is a first-class geodesic vertex. It offers excellent views of Getafe, Madrid, and the surrounding countryside.
Key features
These isolated hills can be classified as inselbergs. Their main characteristic is their preservation after erosion that has dismantled the surrounding materials. These inselbergs have remained protected from erosion thanks to a more resistant lithology . They are quite useful for geological studies since they are the only remaining remnants of other geological formations that previously covered the region. To map the evolution of the Earth's surface over time due to erosion, it is important to understand the morphology of the landscape at that time. The presence of these isolated hills allows us to do so.
These erosion and sedimentation processes are characteristic of our planet's external geodynamics. These witness hills are also characterized by having been surrounded by water, which is why they are located in areas near rivers that have an outlet to the ocean. According to some studies, these reliefs must have formed between the Early Miocene and Early Middle periods.
This formation is not usually covered with red sediments, as these are already present in the Miocene sedimentation. If you do encounter any reddish sediments, it will only be in the first 3 or 4 meters of the hill.
The páramo is distinguished from the páramos primarily by their size. Páramos tend to extend across the territory and are much higher. Their main difference is that the páramo is found alone and is much smaller. Furthermore, a páramo encompasses an entire ecosystem, with a predominance of shrub vegetation. This leads it to be classified biogeographically as a grassland due to its vegetation type. However, the páramo is not categorized as an ecosystem.
I hope that with this information you can learn more about the witness hill.