Factors controlling weathering

Presentation on the different factors controlling weathering. In this we discuss the basic concepts is weathering and explain in breif the various factors controlling them.

1. FACTORS CONTROLLING WEATHERING SHARIK SHAMSUDHIEN ROLL NO: 183104008

2. Content Weathering Factors Controlling Weathering Endogenetic And Exogenetic factors Different factors Controlling Weathering References

3. Weathering The process of disintegration and decomposition of rocks insitu is generally called weathering. It means weathering is a static process. According to C.D. Oilier (1969) ‘weathering is the breakdown and alteration of minerals near the earth’s surface to products that are more in equilibrium with newly imposed physico -chemical conditions.’ Weathering is essentially the breakdown of rocks due to chemical and mechanical processes at their places. Weathering is the breaking down of rocks and other materials on the earth’s surface 


4. Factors Controlling Weathering The nature and magnitude of weathering differs from place to place and region to region. Weathering of rocks is affected and controlled by the agents of weathering, lithological and structural characteristics of rocks, height and slope factors. Besides, climatic conditions, topography and reliefs , flora and microfauna also affect different processes of weathering to greater extent. For example, disintegration of rocks is more effective in hot and dry region and in the regions where frost action is more dominant while chemical decomposition is more prevalent in hot and humid and temperate humid regions .

5. The Geological Weathering factors which are related to the rock characteristics are called as Endogenetic , Such as Mineral composition Rock Structure Particle size The factors other than rock characteristics; pertaining to the external environment are called Exogenetic , Such as Climate Water Gravity Pollution And other Weathering factors 


6. CLIMATE This is the most important factor affecting weathering of rocks. The extent of weathering is dependent on the average atmospheric condition prevailing in a region over a long period of time. There are two factors that play in weathering, they are :- Temperature and Precipitation . Warm climates affect by chemical weathering while cold climates affect by physical weathering (particularly by frost action). In either case the weathering is more pronounced with more moisture content. At higher temperatures chemical reactions are likely to take place faster. Because of abundance of moisture and high temperature leaching process and solution of rocks are more effective in the humid tropics .

7. Biological activities are supported by hot moist climates. In fact a hot moist climate provides the most ideal environment for fast chemical weathering . The rocks in dry temperate climates are more susceptible to mechanical weathering than chemical weathering because alternate expansion and contraction of cracks, fractures and joints of rocks due to alternate freeze and thaw of water accumulated in these cracks and fractures weaken the rocks . Physical weathering by frost action is most likely in cold climate where freeze and thaw occur alternately during the cold weather. In this case again precipitation is the main factor. In the absence of water ice cannot form and frost action is not possible. Hence an effective frost action occurs in the cold moist climate.

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9. PARTICLE SIZE Most weathering occurs on exposed surfaces of rocks and minerals. Rate of chemical weathering is affected by size of rock particles . If the rock pieces are smaller , the weathering is faster. This is because if the rock pieces are smaller, the surface area exposed to weather action is greater. The more surface area a rock has, the more quickly it will weather. When a block is cut into smaller pieces, it has more surface area. Therefore weathering is faster than a large block of rock .

10. MINERAL COMPOSITION AND STRUCTURE OF ROCKS Since weathering involves disintegration and decomposition of rocks and hence mineral composition, joint patterns, layering system, faulting, folding etc. largely affect the nature and intensity of weathering . For example, carbonate rocks (e.g. calcium carbonate, magnesium carbonate etc .) having more soluble minerals are easily affected by chemical weathering . Well jointed rocks are more subjected to mechanical disintegration. Rocks having vertical strata are easily loosened and broken down due to temperature changes, frost action, water and wind actions . On the other hand, the rocks having horizontal beds are more compact and are less affected by the mechanisms of disintegration and decomposition .

11. We know, the chemical properties of a rock depend on the mineral composition to a great extent. Mineral in a rock may readily react with acids, water or oxygen causing considerable weathering. For example limestone can get severely acted upon by even very mildly acidic rainwater. Limestone caves, underground caves, cavern, or Karst topography are a result of this kind of weathering. Karst topography usually forms sinkholes . Granite on the contrary mostly containing silica remains unaffected by such agents Some minerals resist weathering. Quartz is a mineral that weathers slowly. Rocks made up of minerals such as feldspar, calcite, and iron, weather more quickly

12. Honeycomb Weathering Sandstone Oregon coast, U.S

13. EXPOSURE The extent of exposure i.e. the extent to which the rock comes into contact with the agents of weather is an important factor affecting the weathering. In some situations, vegetation , soil, ice, etc. may cover a rock , thereby reducing the area exposed to weather action . Such rocks so protected weather slowly compared to rocks whose surfaces are wholly exposed to weather. Slope of the region is also a factor affecting weathering. Where the slopes are steep, loose materials are displaced downhill either by gravity or by erosion resulting in continuous exposure of the fresh rock.

14. NATURE OF SLOPE/GRAVITY Ground slope controls mechanical disintegration of rocks and mass movement of weathered products down the slope. The rocks in the regions of steep hillslope are easily disintegrated due to mechanical weathering and the weathering materials are instantaneously moved down the hillslope in the form of rock-fall, debris fall and slide, talus creep etc. Instantaneous removal of weathering products allows continuous exposure of rocks to atmospheric conditions for further weathering . The regions of gentle and moderate ground slope are less affected by mechanical disintegration

15. Force of gravity can pull rocks and sediment towards the Earth. The rocks falling and colliding with other rocks. Oddiecombie , UK

16. FLORAL EFFECTS The nature of weathering is largely determined by the presence or absence of vegetation’s in a particular region . It may be pointed out that vegetation is partly a factor of weathering and partly a protector of rocks . In fact, vegetation’s bind the rocks through their network of roots and thus protect them from weathering and erosion but the same time the penetration of roots weakens the rocks by breaking them into several blocks. Dense vegetation’s protect the ground surface from the direct impact of sun rays. The microorganisms associated with the roots of plants and trees encourage decomposition and disintegration of rocks through physiobiochemical weathering.

17. TIME AND POLLUTION The process of weathering is a time taking process . The duration of time for which a rock is exposed to weather determines the extent of weathering. Very strong rocks, however strong they might be will severely undergo weathering in hundreds of years. Pollution speeds up weathering. Factories and cars release carbon dioxide and other gases into the air. These gases dissolve in the rainwater, causing acid rain to form . Acid rain contains nitric and sulfuric acid , causing rocks and minerals to dissolve faster.

18. References The Earths Dynamic surface by K. Siddhartha Weathering of Rocks : Meaning, Controlling Factors and Types- Sirisha P._Geography Notes.com http://www.geographynotes.com/rocks/weathering-of-rocks-meaning-controlling-factors-and-types-rocks-geography/2350 http ://www.yourarticlelibrary.com/geology/weathering-of-rocks-5-factors-geology/91154 http://the-gneiss-blog.tumblr.com/post/125917254829/factors-affecting-weathering 


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