Geomorphic Processes - 2 Class 11 Geography

Mass Movements

• Mass Movements: These are situations where rocks and debris move downhill because of gravity. Unlike some other processes like wind, water, or ice, gravity is the main force causing the movement. However, the debris can pick up things like air, water, or ice as they move.
• Weathering: This is when rocks break down over time. While not necessary for mass movements, it does make them more likely to happen, especially on slopes where the rocks have already broken down a bit.
• Not Erosion: Mass movements are different from erosion, where materials are worn away by things like water and wind. In mass movements, the materials mostly stay in one place but shift around due to gravity.

• Causes of Mass Movements: There are several things that can trigger mass movements:
  • Removing support from below the materials above (like digging underneath).
  • Making the slope steeper or higher.
  • Adding more weight to the slope, either naturally or by adding stuff.
  • Heavy rain can saturate the soil and make it slippery, causing movement.
  • Removing material from the slope.
  • Things like earthquakes, explosions, or machinery can also trigger movement.
  • Too much water seeping into the ground.
  • Draining a lot of water from lakes or rivers can lead to slow movement in riverbanks.
  • Removing plants from the area can make the soil more prone to movement.
• Types of Movements: There are three main ways that mass movements happen:
  • Heave: This is when the soil moves upward because of things like frost.
  • Flow: It's like a slow, downhill movement of soil, almost like a thick liquid.
  • Slide: This is when a big chunk of soil or rock slides down the slope.

So, mass movements are basically when rocks and debris move down slopes because of gravity, and there are various reasons why this can happen. It's not the same as erosion, and weathering can make it more likely to occur.

Slow mass Movements

• Creep:
  • Creep is a very slow movement of soil or rock debris down a hillside.
  • It happens on moderately steep slopes that are covered with soil.
  • The movement is so slow that you can't see it happening unless you observe it for a long time.
  • You might notice things like fence posts or telephone poles leaning downhill because of this slow creep.

• There are different types of creep, depending on the material involved, like soil creep, talus creep, rock creep, and rock-glacier creep.
• Solifluction:
  • Solifluction is another slow movement of soil or fine-grained rock debris, but it's like a slow flow downhill.
  • This usually occurs in places where it's moist and temperate (not too hot or cold).
  • It happens when the ground is frozen deep down, but the top part thaws, and there's a lot of rain.
  • The upper part of the soil gets wet and flows downhill because the lower part can't soak up the water.
  • It's like a slow, muddy river of soil moving down the slope.

In simple terms, both creep and solifluction are very gradual movements of soil and rocks down a hill, but they happen for different reasons and can affect things like poles and fences by making them tilt downhill.

Rapid Movements

• Earthflow:
  • Happens in places with a lot of moisture in the air (humid regions).
  • Occurs on slopes that can be gentle or steep.
  • It's like wet, muddy earth sliding down a hill.
  • Sometimes, the earth piles up in steps and leaves a curved mark at the top and a bulge at the bottom.
• Mudflow:
  • Occurs when there's a lot of rain and the ground is not covered with plants.
  • Layers of soil that have been weathered (broken down by natural processes) get filled with water and flow like a river of mud.
  • It can be very dangerous because it can cover roads, bridges, and houses when it reaches flat areas.
• Debris Avalanche:
  • Happens in places with a lot of moisture, with or without plants.
  • It occurs in narrow paths on very steep slopes.
  • This kind of movement can be even faster than a mudflow.
  • It's similar to when a lot of snow rushes down a mountain.
• Bedrock Slide:
  • This happens when the hard, solid rock beneath the soil starts sliding down a steep slope.
  • This can occur in slopes made of soft rocks like shale or rocks that have been weathered a lot.
• Volcanic Mudflows:
  • Occur on the sides of volcanoes, especially when they're erupting or have just erupted.
  • Volcanic ash, dust, and other bits mix with rain and flow down like a stream of mud, causing a lot of damage to homes and other buildings.

These movements can be dangerous and cause a lot of damage to the environment and human structures. It's important to be aware of these natural processes, especially if you live in an area where they might occur.

Landslides

• Rapid Movements: These are quick movements of materials on a slope.
• Perceptible Movements: These are movements that we can see or notice.
• Dry Materials: The materials involved in these movements are not wet or liquid; they are dry.
• Size and Shape Depend on: The size and shape of the materials moving depend on:
  • The type of rock involved.
  • How much the rock has been affected by weathering (breaking down over time).
  • How steep the slope is.
• Slump: This is when a chunk of rock or debris slips and rotates backward on a slope.
• Debris Slide: This is when earth debris (like soil and rocks) quickly rolls or slides down a slope without rotating backward.
• Rockslide: This is when individual pieces of rock slide down a slope along their natural layers, cracks, or fault lines.
• Rock Fall: This is when big blocks of rock fall freely down a steep slope without sticking to the slope.

Erosion and Deposition

• Erosion:
  • Erosion is the process where rocks and soil are gradually worn away and moved to other places.
  • This happens when big rocks break into smaller pieces due to various factors like weathering, and then natural forces like water, ice, wind, and waves remove and carry away these pieces.
  • These natural forces are called "geomorphic agents" and include things like rivers, groundwater, glaciers, wind, and ocean waves.
  • These agents can also cause abrasion, which means they can further wear down rocks and surfaces as they move.
  • Erosion essentially makes the land and landscape slowly wear down and change over time.
• Deposition:
  • Deposition is what happens after erosion. It's like the opposite of erosion.
  • When the erosional agents like water or wind slow down, they can't carry the rocks and soil as effectively anymore.
  • So, they start to drop or settle the materials they were carrying.
  • This usually happens on gentler slopes or in places where the erosional agents lose their energy.
  • Over time, this settling of materials leads to the formation of new landforms and changes in the landscape.

So, erosion is the process of rocks and soil being removed and transported, while deposition is when these materials settle down in a new location. Together, these processes shape and change the Earth's surface.

Soil Formation

• Soil is the collection natural bodies on the earth’s surface containing living matter and supporting or capable or supporting plants.
• Soil is a dynamic material in which many chemical, biological, and physical activities go on constantly. It is the result of decay, it is also a medium of growth. It is changing and developing body. Characteristics are changing from season to season.
• Too cold, too hot, and dry areas biological activity stops. organic matter increases when leaves fall and decompose.

Process of Soil Formation

• Weathering is basic process for soil formation.
• The weathered material is transported and decomposed due to bacteria lichens and moss.
• The dead remains increases the humus of the soil. minor grasses and ferns can grow. Bushes, trees also grow. plants roots and burrowing animals help the soil formation.

Soil Forming Factors

Five basic factors control the formation of soils:

• Parent material
• Topography
• Climate
• Biological activity
• Time

1. Parent Material

• Parent material is a passive control factor in soil formation. Parent materials can be any in- situ or on-site weathered rock debris (residual soils) or transported deposits (transported soils).
• Soil formation depends upon the texture (sizes of debris) and structure (disposition of individual grains/particles of debris) as well as the mineral and chemical composition of the rock debris/deposits.
• Nature and rate of weathering and depth of weathering mantle are important considerations under parent materials. There may be differences in soil over similar bedrock and dissimilar bedrocks may have similar soils above them. But when soils are very young and have not matured these show strong links with the type of parent rock. Also, in case of some limestone areas, where the weathering processes are specific and peculiar, soils will show clear relation with the parent rock.

2. Topography

• Topography like parent materials is another passive control factor.
• The influence of topography is felt through the amount of exposure of a surface covered by parent materials to sunlight and the amount of surface and sub-surface drainage over and through the parent materials.
• Soils will be thin on steep slopes and thick over flat upland areas. Over gentle slopes where erosion is slow and percolation of water is good, soil formation is very favourable.
• Soils over flat areas may develop a thick layer of clay with good accumulation of organic matter giving the soil dark colour. In middle latitudes, the south facing slopes exposed to sunlight have different conditions of vegetation and soils and the north facing slopes with cool, moist conditions have some other soils and vegetation.

3. Climate

• It is an active factor in soil formation.
• Climatic elements are:
  •  moisture in terms of its intensity, frequency and duration of precipitation - evaporation and humidity;
  • temperature in terms of seasonal and diurnal variations
• Precipitation increases the biological activity.
• Excess of water helps to transport the dissolved particles to downward (eluviation).
• Deposition of these particles is called ‘Illuviation’.
• Heavy rainfall removes the calcium, magnesium, sodium, potasium along with silica.
• Removal of silica is called desilication.
• In dry areas excess of evaporation leads to deposition of salts on the surface of the soil.
• These salt layers are called ‘hard pans’ in the hot deserts.
• In tropical climates, under moderate rainfall conditions calcium carbonate nodules are formed.

4. Biological Activity

• The vegetative cover and organisms that occupy the parent materials from the beginning and also at later stages help in adding organic matter, moisture retention, nitrogen etc.
• Dead plants provide humus, the finely divided organic matter of the soil. Some organic acids which form during humification aid in decomposing the minerals of the soil parent materials.
• Intensity of bacterial activity shows up differences between soils of cold and warm climates. Humus accumulates in cold climates as bacterial growth is slow.
• In humid tropical and equatorial climates, bacterial growth and action is intense and dead vegetation is rapidly oxidised leaving very low humus content in the soil.
• Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation. Rhizobium, a type of bacteria, lives in the root nodules of leguminous plants and fixes nitrogen beneficial to the host plant.
• The influence of large animals like ants, termites, earthworms, rodents etc., is mechanical, but, it is nevertheless important in soil formation as they rework the soil up and down. In case of earthworms, as they feed on soil, the texture and chemistry of the soil that comes out of their body changes.

5. Time

• Time is the third important controlling factor in soil formation. The length of time the soil forming processes operate, determines maturation of soils and profile development.
• A soil becomes mature when all soil-forming processes act for a sufficiently long time developing a profile.
• Soils developing from recently deposited alluvium or glacial till are considered young and they exhibit no horizons or only poorly developed horizons.
• No specific length of time in absolute terms can be fixed for soils to develop and mature.