Why is natural erosion a beneficial process

Relief compensation through soil erosion

structure

1 Introduction

2. Introduction: What types of erosion are there?

3. Basics of soil erosion
3.1. Linen-like soil erosion
3.2. Extensive soil erosion
3.3 Aeolian soil erosion

4. The rules of geoecological-geomorphodynamic activity and stability
Stability rule (AS1):
Activity rule (AS2)
Anthropogenic partial activity rule (AS3):

5. General consequences of soil erosion

6. Consequences of soil erosion for the settlement, or rather for the settlers

7. Example of linen-like and extensive erosion

8. Heavy rain events in history

9. Current examples

10. Aeolian transport

11. Quantification of the runoff processes

12. Special cases - The settlement is relocated, the agricultural production areas are retained

13. Summary

14. Literature:

1 Introduction

When dealing with the topic of “relief compensation through soil erosion”, the general starting situation must first be considered. By and large, geologists see the state of Central Europe as relatively stable since the beginning of the Holozaen, with the exception of the Alpine zones. Excluding the alpine zones, no major erosive events are expected. By and large, this is also true; which means that, viewed from a bird's eye view, the relief still roughly corresponds to the relief in the early Holozaen.

The north German lowlands, for example, as part of the “Great European Plain”, have mainly been shaped by the major glaciation phases of the Pleistocene. This process of shaping can still be seen clearly in the landscape today and it is also possible in this landscape to assign the individual landscape-forming processes to the individual glaciation phases.

We can also clearly assign the mountains to the individual ore formation phases. In Germany and also in other countries these are the Caledonian, the Varizian, and the Alpine mountain building phases. From this it follows that the erosion was and is probably not so severe that a large-scale relief of the relief occurs. Nevertheless, due to the force of gravity, there is always a tendency to equalize the relief.

So there are many relatively small-scale events in which there is erosion and accumulation and thus, according to the laws of gravity, also to a relief compensation. It is precisely these relatively small-scale events, which have a major impact on archeology and are therefore of great importance for the subject, should be considered here.

2. Introduction: What types of erosion are there?

Erosion is the transport of material. There are basically three types of erosion. The transport of material through water, the so-called fluvial erosion, the transport of material through ice masses, the glacial erosion and the transport of material through the wind is referred to here as aeolian erosion (Murawski, 1957).

Since there were only minor temperature drops in the Holozaen, glacial erosion can be neglected in Central Europe, again with the exception of the alpine regions, since no large ice masses could form in the area considered here.

The precondition for fluvial and aeolian erosion is that the terrain offers sufficient attack surface, i.e. that it is exposed.

In these explanations, the erosion of the soils in the Holozaen should now be considered and its effects explained. For this purpose, the conditions and processes involved in soil erosion must be presented in more detail here.

3. Basics of soil erosion

It is about processes in which raindrops, flowing water or wind impacting the surface of the terrain trigger processes in which soil particles are detached, transported and deposited (Bork et all., 1998).

In the forested regions that are not influenced by humans, natural erosion does not and did not occur, or only to a small extent. In this way, the erosion influenced by humans in formerly forested regions or in regions that have been reforested after the abandonment of use can be clearly identified.

Human interventions cannot directly trigger soil erosion, but only enable, intensify, reduce or even prevent it.

A distinction is mainly made between extensive soil erosion and linear soil erosion.

3.1. Linen-like soil erosion

The runoff of water along bundling paths leads to soil erosion. Depending on the extent, a distinction is made between groove erosion on the one hand and notch erosion on the other.

In the case of groove erosion, heavy rain or snowmelt cuts into small grooves, which are, however, compensated for by the usual tillage measures.

With notch erosion, too, heavy rain or snowmelt only lead to the formation of small grooves. If the runoff continues, these grooves deepen and, as a result of receding erosion, deep notches are finally formed. These notches can no longer be closed by normal tillage.

3.2. Extensive soil erosion

Erosion is caused by raindrops hitting the soil surface or by water flowing on the soil surface. In the long term, the soil surface is more or less evenly deepened by the extensive runoff on the surface. In this context, one speaks of creeping soil erosion. Even with extensive soil erosion, there are many small drainage grooves, so there is linear erosion here as well. However, the grooves are always leveled out when the soil is tilled. Therefore, they are not noticed by the worker, in most cases the farmer, and the impression is of extensive removal of the soil.

3.3 Aeolian soil erosion

In addition to the two forms of soil erosion described above, which were associated with aquatic transport, there is a kind of special case, the aeolian soil erosion. Here, the sands are blown out by the wind on exposed sand surfaces, which were created, for example, by pest or overgrazing, and deposited again at another location. Here, too, extensive soil erosion occurs.

4. The rules of geoecological-geomorphodynamic activity and stability

Heinrich Rohdenburg (1969/1971) developed the rules of geoecological-geomorphodynamic activity and stability to understand the landscape development processes. These rules are of crucial importance for understanding the historical development of the holozene soils. They should therefore be mentioned again here and read as follows:

Stability rule (AS1):

Natural vegetation (in Central Europe almost without exception forests outside of the high mountain areas), which completely covers the soil surface, usually completely protects against erosion even in heavy rain (exceptions are in particular steep slopes at risk of landslides; see Bibus 1986).

Intensive soil formation marks geomorphologically stable times. In the soils of Central Europe, acidification processes dominate under the natural forest vegetation of the humid, warm-time stability phase. First of all, the topsoil is decalcified and browned; Sound shifting, podsolization and pseudo-glazing follow in many places.

Activity rule (AS2)

Gradual or abrupt, thermal or hygric (hygro - humid) climate changes can destroy large areas of the natural vegetation that protects the soil surface from erosion. The natural destruction or loosening of vegetation enables natural erosion, transport and accumulation processes, which are primarily triggered by heavy rainfall. The climate-related destruction of the natural, warm-period vegetation in humid and semi-humid regions of the earth and the subsequent natural erosion and accumulation change the conditions, functions, structures and processes of soils.

Anthropogenic partial activity rule (AS3):

The human influence interrupts or ends the natural geomorphological stability phase in previously completely vegetation-covered areas. Clearing of the natural Central European forest vegetation and subsequent arable farming changes the soil formation and enables soil erosion processes on the areas used in times of low vegetation cover.

Figure not included in this excerpt

Fig.1: The relationship between clearing, cultivation and soil erosion. (Drawing H. Grönwald, from Gringmuth-Dallmer, 1997, p.12)

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