Find in Text 6 English equivalents for the following words and expressions and memorize them.

1) материнская порода

2) подстилающая порода

3) торф

4) рыхлые обломки породы

5) одновременно

6) сцементированный песчаник

7) раздробляться, измельчаться

8) растворимое вещество

9) нерастворимое вещество

10) отлагаться, оседать

11) аллювиальные отложения

12) морские отложения

13) оледенение

14) обнаженная горная порода

15) крутой склон

16) ледниковые отложения

17) морена

18) иметь общее происхождение (быть генетически связанным)

19) почвенный горизонт

20) почвенный профиль

 

Translate the text from English into Russian.

TEXT 6

SOIL AS A NATURAL BODY

THE PARENT MATERIAL OF SOILS

Soil formation, or the development of soils that are natural bodies, includes two broad processes. First is the formation of a parent material from which the soil evolves and, second, the evolution of soil layers. Approximately 99 percent of the world's soils develop in mineral parent material that was or is derived from the weathering of bedrock, and the rest develop in organic materials derived from plant growth and consisting of muck or peat.

Bedrock Weathering and Formation of Parent Material

Bedrock is not considered soil parent material because soil layers do not form in it. Rather, the unconsolidated debris produced from the weathering of bedrock is soil parent material. When bedrock occurs at or near the land surface, the weathering of bedrock and the formation of parent material may occur simultaneously with the evolution of soil layers. This is shown in Figure 2.2, where a single soil horizon, the topsoil layer, overlies the R layer, or bedrock. The topsoil layer is about 12 inches (30 cm) thick and has evolved slowly at a rate controlled by the rate of rock weathering. The formation of a centimeter of soil in hundreds of years is accurate for this example of soil formation.

Rates of parent material formation from the direct weathering of bedrock are highly variable. A weakly cemented sandstone in a humid environment might disintegrate at the rate of a centimeter in 10 years and leave 1 centimeter of soil. Conversely, quartzite (metamorphosed sandstone) nearby might weather so slowly that any weathered material might be removed by water or wind erosion. Soluble materials are removed during limestone weathering, leaving a residue of insoluble materials. Estimates indicate that it takes 100,000 years to form a foot of residue from the weathering of limestone in a humid region. Where soils are underlain at shallow depths by bedrock, loss of the soil by erosion produces serious consequences for the future management of the land.

Sediment Parent Materials

Weathering and erosion are two companion and opposing processes. Much of the material lost from a soil by erosion is transported downslope and deposited onto existing soils or is added to some sediment at a lower elevation in the landscape. This may include alluvial sediments along streams and rivers or marine sediments along ocean shorelines. Glaciation produced extensive sediments in the northern part of the northern hemisphere. Four constrasting parent material-soil environments are shown in Figure 2.3. Bare rock is exposed on the steep slopes near the mountaintops. Here, any weathered material is lost by erosion and no parent material or soil accumulates. Very thick alluvial sediments occur in the valley. Very thick glacial deposits occur on the tree-covered lateral moraine that is adjacent to the valley floor along the left side. An intermediate thickness of parent material occurs where trees are growing below the bare mountaintops and above the thick alluvial and moraine sediments. Most of the world's soils have formed in sediments consisting of material that was produced by the weathering of bedrock at one place and was transported and deposited at another location. In thick sediments or parent materials, the formation of soil layers is not limited by the rate of rock weathering, and several soil layers may form simultaneously.

SOIL FORMATION

Soil layers are approximately parallel to the land surface and several layers may evolve simultaneously over a period of time. The layers in a soil are genetically related; however, the layers differ from each other in their physical, chemical, and biological properties. In soil terminology, the layers are called horizons. Because soils as natural bodies are characterized by genetically developed horizons, soil formation consists of the evolution of soil horizons. A vertical exposure of a soil consisting of the horizons is a soil profile.

(H.D. Foth, Fundamentals of Soil Science)

Answer the questions.

1) What is parent material? How does its formation occur?

2) What is bedrock?

3) What is the difference between parent material and bedrock?

4) What is the difference between weathering and erosion?

5) What is a soil horizon?

6) What is a soil profile?