A.D.M. COLLEGE FOR WOMEN (AUTONOMOUS), NAGAPATTINAM DEPARTMENT OF GEOLOGY PHYSICAL GEOLOGY II B.Sc. GEOLOGY UNIT-1 PHYSICAL GEOLOGY: Physical geology is the branch of geology that deals with the processes that change the physical landscape of the planet. Weathering: The rocks break and undergo decay under the influence of the atmospheric agencies like wind, sun, frost, water and organisms and produce soil. This phenomenon is called weathering. Wind, sun, frost, water and organisms Soil Rock decay breaks Weathering process: It includes two processes: • Disintegration • Decomposition Weathering: • Erosion • Transportation • Deposition Erosion: Erosion is a process which includes the destruction of existing rocks and removal for the product from the site of destruction. Denudation: The combined process of weathering and erosion is known as denudation. Transportation: The process through which the eroded materials are carried from one place to another is known as transportation. Deposition: The process through which the eroded particles get deposited in a place where it meets an obstacle or a basin is known as deposition. Types of weathering: There are three types of weathering. They are as follows: a) Physical weathering b) Chemical weathering c) Biological weathering a)Physical weathering: • Physical weathering is also known as mechanical weathering. • Physical weathering occurs when physical forces break a rock into smaller and smaller pieces without changing the rock mineral composition. • These forces are wind, water, waves and gravity. • This type of weathering happens especially in places where there is little soil and few plants grow such as in mountain regions and hot deserts. • It can occur due to temperature, pressure, frost etc. i)Frost wedging: When water freezes, it expands about nine percent of volume. In nature water enters into cracks of rocks. Upon freezing expands and exerts great pressure on the walls of cracks. As a result the rock breaks into pieces. This process is called frost wedging. ii) Exfoliation: • It is mainly a physical weathering process in which large sheets of rock peel of from an outcrop. • In exfoliation reduction in pressure due to removal of overlying rock plays an important part. • As each slab breaks off, it releases weight from the underlying mass. • As a result its outer layers expand and separate from the rock mass. iii)Thermal expansion: • It occurs due to the repeated heating and cooling of rocks. • It mostly occurs in desert environments. • In the rocks heating causes expansion and cooling causes contraction. b)Chemical weathering: • Chemical weathering is a process in which rocks are broken down by chemical decay of minerals. • Water is the most important agent of chemical weathering. • Two other important agents of chemical weathering are carbon dioxide and oxygen. i)Water: Although water in pure form is inactive, it becomes a powerful chemical agent when a small amount of oxygen and carbon dioxide are dissolved in it. Rain water usually contains these gases. The main reactions involved in the chemical weathering are oxidation, hydration, carbonation and solution. Oxidation: The oxygen present in the water in dissolved state oxidizes some minerals. When iron in rock reacts with oxygen it forms iron oxide, which weakens the rock. Limonite and hematite are very common products of oxidation. Hydration: In hydration water molecules combine chemically with minerals to produce new compounds. The formation of gypsum (CaSO2.2H2O) from anhydrite (CaSO4) is a good example of hydration. Carbonation: Carbon dioxide dissolves in water to form carbonic acid (H2O3). Carbonic acid is an effective weathering agent. Granite under the influence of carbonic acid it weathers into clay. ii) Organisms: Many dead organisms produce organic acids as they decay. These acids increase the solvent power of water. For example the solubility of silica alumina and iron is much greater in the presence of organic acid. c) Biological weathering: • Biological weathering is caused by plants and animals. • Plants and animals release acid forming chemicals that cause weathering and also contribute to the breaking down of rocks and landforms. Factors influencing rate of weathering • Rock structures- chemical/ mineral composition • Topography • Climate • Vegetation • Time Products of weathering: • The products of weathering and erosion are the unconsolidated materials that we find around us on slopes, beneath glaciers, in stream valleys, on beaches, and in deserts. • The nature of these materials ie their composition, size, degree of sorting, and degree of rounding is determined by the type of rock that is being weathered, the nature of the weathering, the erosion and transportation processes, and the climate. Products Of Weathering: • Regolith • Sediments • Dissolved ions Soil: Any solid unconsolidated material lying on top of bedrock is called regolith. A portion of regolith which supports the growth of plants is called soil. A-Horizon: Uppermost layer of the soil profile. It is also known as surface soil. It contains organic matter and micro-organisms. B-Horizon: Also known as subsoil and zone of accumulation. Materials leached in A- horizon are deposited here. C-Horizon: The lower horizon. It consists of partly altered parent rock material. WEATHER AND CLIMATE Sl.No. WEATHER CLIMATE 1 The day to day information of Climate is the statistical information of atmospheric changes of a particular the average weather condition of a area at a specific time is called specific region for more than 30years. weather. 2 The weather of a place includes the The climate of a country or zone short-term atmospheric condition. includes the long term average Also, these atmospheric conditions can atmospheric conditions. Thus, the change within a short period like climate is average weather information minutes, hours, days etc.. observed over decades. 3 The atmospheric elements of weather When the atmospheric elements of are air pressure, humidity, wind, weather are observed over the decades, temperature, rain, cloudiness, storms, those become the affecting conditions of snow, precipitation etc. These climate. These conditions can include conditions can affect the weather of the temperature, humidity, wind etc. place within a short time. 4 The weather of a particular location The climate of a country significantly can impact the day to day human life impacts industries, agriculture, the like occupation, transportation, livelihood of the inhabitants of that communication, agriculture etc. geographical locale. 5 Weather conditions change very Climate conditions change over a long frequently. period. 6 The meteorological department of a Institutes of climate studies observe and place observes the changes in weather predict the changes in climate. This conditions. The study of weather study is called climatology. forcasting is known as meteorology. Economic importance of weathering: • Produces unconsolidated material from which soil is formed. • Provides plant nutrients. • Results in the formation of secondary minerals, the most important group being the clay minerals. • It weakens the rocks making them easier for people to exploit. • Weathering of rocks and deposits helps in concentration of some valuable ores of manganese, aluminum, iron copper etc. Which have a great significance in the economy of the country. Atmosphere: The atmosphere is the blanket of air that surrounds the earth. Composition of air: • Nitrogen -78 • Oxygen -21 • Other gases -1 • Greenhouse gases –Carbon dioxide, methane, water vapor etc. Earth's atmosphere is divided into five main layers: the exosphere, the thermosphere, the mesosphere, the stratosphere and the troposphere. There is no distinct boundary between the atmosphere and space, but an imaginary line about 62 miles (100 kilometers) from the surface, called the Karman line, is usually where scientists say atmosphere meets outer space. Troposphere: • It is the layer closest to the Earths surface. • Its thickness is about 12km. • Temperature decreases with altitude. • Weather changes takes place. • Vertical air currents. • Contains 75% of air. • Composition- Oxygen and nitrogen. Stratosphere: • Second layer of atmosphere. • Extends upto 50km. • Horizontal air currents. • Temperature increases with altitude. • Contains the ozone layer in the upper part. • Jet planes travels here. • Contains 24% of air. • Uppermost part of stratosphere is known as stratopause. Mesosphere: • Third layer of the atmosphere. • Extends upto 90km. • Temperature decreases with altitude. • Coldest layer. • Meteors burn here. • Uppermost part of Mesosphere is known as mesopause. Thermosphere: • Fourth layer of the atmosphere. • Extends upto 800km. • Hottest layer. • Temperature increases with altitude. Uppermost part of the thermosphere is called thermopause. Exosphere: • Outermost layer of the Earths atmosphere. • It is composed of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide. Wind The air current in motion is called wind. Wind is an important agent of erosion, transportation and deposition. Its work is particularly seen in arid regions. AEOLIAN PROCESSES AND LANDFORMS: Wind erosion: Wind does erosion in three ways: a)Deflation b)Abrasion c)Attrition a)Deflation: • Lifting and removal of loose materials is known as Deflation. • By this process land surface is gradually lowered. • In many desert paces deflation produces hollows or basins with their bottom at water table. • Such basins