Go through these RBSE Class 11 Geography Notes Chapter 7 Earthquakes and Volcanoes contain important concepts so that students can score better marks in the exam.
Rajasthan Board RBSE Class 11 Geography Notes Chapter 7 Earthquakes and Volcanoes
- The crust of the earth is always changing due to endogenetic and exogenetic forces.
- Earthquake is a sudden natural disaster produced by endogenetic forces.
- Shaking of the earth’s surface is known as earthquake. Normally, earthquake refers to sudden shaking taking place on some part of the surface due to geological forces.
Reasons for Origin of Earthquake
- Faulting, volcanic activities, hydraulic weight, contraction of the crust, Isostatic adjustment, Elastic-Rebound Theory, discharge of gases along with plate tectonics, landslides, falling off of ceilings of cliffs and caves are considered responsible for the origin of earthquakes.
- Earthquakes also originate from nuclear explosions carried out by mankind, explosions in mining regions and from deep holes.
- The science which studies earthquakes is known as Seismology.
- An instrument known as Seismograph is used to record seismic waves.
- The place from where an earthquake originates is known as seismic focus and the place where the seismic waves are firstly experienced is known as epicentre.
- Shaking takes place in the rocks due to shock experienced at the seismic focus, due to which waves originate.
- Earthquake waves are of three types- P waves, S waves and L waves.
- P waves are the first to reach the earth’s surface. These waves travel through all the three mediums- solid, liquid and gaseous.
- S waves travel only through the solid part. They disappear in liquid part.
- L waves are surface waves. These waves cause maximum destruction.
Types of Earthquakes
- Earthquakes are classified on the basis of their nature and causes.
- Earthquakes are normally classified into artificial earthquakes, natural earthquakes and on the basis of their position.
- Natural earthquakes have been classified into volcanic earthquakes, tectonic earthquakes, isostatic earthquakes and plutonic earthquakes.
- According to their position, earthquakes are classified into land and oceanic earthquakes.
World Distribution of Earthquakes
- Most of the world’s earthquakes are experienced in newly folded mountains, volcanic regions and coastal regions.
- There are three belts of earthquakes in the world-(i) Circum-Pacific Ocean belt, (ii) Mid-Continental belt, (iii) Mid-Atlantic Ridge belt.
- World’s two-third earthquakes occur in the Pacific Ocean belt and 21 per cent earthquakes occur in the Mid-Atlantic Ridge belt.
Effects of Earthquake
- Earthquake is a natural disaster which produces extremely destructive conditions on the earth’s surface in a very short time period.
- Positive and negative impacts of earthquakes are visible on the surface.
- Loss of life and property, breaking of dams, disorganisation of transport routes, collapsing of buildings, evolution of Tsunamis, etc. are the negative effects of earthquakes. Emergence of submerged regions, information about the structure of the earth, sharpening of the depth of ports, increasing in groundwater level, etc. are the positive effects of earthquakes.
- Volcano is a sudden activity produced by geological forces in which gas, rocks, substances and hot magma erupt from the ridge or crack of the earth’s surface.
- Volcano is a form of vulcanicity.
Causes of Vulcanicity
- Vulcanicity is the result of isostatic disequilibrium, emergence of gases, increase in temperature inside the earth, decline in pressure and plate tectonics.
- A volcano erupts due to structural changes in the interior regions of the earth, condition of vapour, increase in volume, decrease in the pressure of rocks and due to the movement of plates.
Types of Volcanoes
- Volcanoes have been categorized on the basis of duration of emission and nature of emission.
- On the basis of duration of emission, volcanoes have been classified into Active, Dormant and Extinct volcanoes.
- On the basis of nature of eruption, volcanoes have been classified into volcanoes of central eruption and volcanoes of fissure eruption.
- Volcanoes with central eruption have been classified into Hawaiian eruption, Stromboli eruption, Volcanian eruption Pelean eruption volcanoes.
- Pelean eruption volcanoes erupt with the most violent explosion.
Substances emitted from Volcanoes
- Mainly gases and water vapour, solid substances, liquid substances are included in the substances erupted from volcanoes.
- Gases such as carbon dioxide, sulpher dioxide, carbon monoxide, ammonium chloride and solid substances such as rocks of minute to massive size are erupted from volcanoes.
- In the form of liquid substances, magma is produced under the surface and lava is erupted above the surface.
World Distribution of Volcanoes
- Volcanoes are mainly distributed in the Circum-Pacific Ocean belt, Mid-Continental belt, Mid-Atlantic Ridge belt and East African belt.
- The Circum-Pacific Ocean belt is also known as the Ring of Fire.
- The Circum-Pacific Ocean belt starts from Mount Erebus of Antarctica and passes by Andes, Rockies Mountains, turns from Alaska and joins the Continental belt while passing by the south-eastern coastal regions.
- Mount Barren, Popa, Elbrus, Etna, Visuvius are the volcanoes of Mid-Continental belt.
- The Mid-Atlantic belt is spread in ‘S’ shape in the Atlantic Ocean.
- East African belt proceeds in the south of Israel from the Red Sea and from the East African rift valley and joins up till Madagascar.
- Minor distribution of volcanoes is found in Hawaiian Islands, Mauritius and Kamero in the Indian Ocean.
Effect of Vulcanicity
- There are creative and destructive effects of vulcanicity.
- Formation of fertile soil, development of mineral belts, etc. are creative effects of vulcanicity.
- Loss of life and property, pollution of the environment, loss to cultural landscape, destruction caused due to submergence of regions in coastal areas, etc. are destructive (harmful) effects of vulcanicity.
Earthquakes and Volcanoes Notes Important Terms
→ Earthquake: A sudden trembling or movement on the earth’s surface, which originates in natural form under the earth’s surface.
→ Volcano: An opening in the earth’s crust from which hot liquid lava, gases, pieces of rocks, ash, water, etc. are erupted.
→ Endogenetic Force: Force which is originated under the earth due to which horizontal and vertical movements take place.
→ Exogenetic Force: Force which is produced or which is active on the earth’s surface which always remains active in levelling the earth’s surface.
→ Isostasy: The state of gravitational equilibrium between the Earth’s crust and mantle which is found between the elevated parts (mountains, plateaus, plains) and depressed parts (seas, oceans) of the earth.
→ Fault: A fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement as a result of rock-mass movement in which rocks get transferred from one place to another place, besides creating an edge on the earth’s surface.
→ Tension: Force which is exerted on the rocks due to pull from the opposite side of the rocks.
→ Compression: Force which is produced due to the pressure exerted from both sides in the form of horizontal force in a region.
→ Cracking: Breaking up of rocks due to action of intolerable force due to the process of exertive forces.
→ Rift Valley: A lowland between two parallel highlands whose breadth is extremely less but the length is more.
→ Vulcanism or Vulcanicity: Volcanic activity under which all the processes from the origin of hot liquid Magma inside the earth’s surface up to its emergence on the surface and the process of cooling down and solidification of the substances is included.
→ Dam or Embankment: A wide and high wall built of rocks or concrete on the estuary or bank of the water-flowing route of a river to stop its water flow, change its direction or to control the flow of water.
→ Radiation: That process by which a substance or object emits radioactive energy in the form of heat. The heat of that substance declines due to this and it gets cooled down.
→ Ocean Deeps: The deepest part of oceanic bottom which is found in a limited region of oceanic bottom and whose incline is extremely sharp.
→ Erosion: Weathering of earth’s surface or rocks by various natural forces. Flowing surface water, underground water, oceanic water, wind, glaciers and ice are the major factors of erosion.
→ Deposit: Deposition is the geological process in which sediments, soil and rocks are added to a landform or landmass.
→ Plate: Fixed landforms are called plates.
→ Divergent Boundaries: When two plates move towards the opposite direction from each other then a new crust is formed which are called divergent boundaries.
→ Convergent Boundaries: When one plate is suppressed under another plate and where the earth’s crust is destroyed, it is known as convergent boundary.
→ Subsidence: Subsidence is the motion of a surface (usually, the earth’s surface) as it shifts downward relative to a datum such as sea level. The process of gradual descent of a large volume of wind or its settling down.
→ Cliff: A cliff is a vertical, or nearly vertical, rock protuberance which is found on a seashore or on hills.
→ Seismology: The science which studies seismic waves on the basis of graph drawn by instrument which records earthquakes.
→ Seismograph: The instrument which is used to record seismic waves.
→ Seismic Focus: The centre which is situated under the earth’s surface from where the earthquake originates.
→ Epicentre: A point situated on the earth’s surface which is right above the centre of the origin of earthquake or seismic focus.
→ Seismic Waves: Waves of energy that are generated by an earthquake or other earth vibration and that travel within the earth or along its surface. This wave firstly reaches the epicentre from where it is transmitted in various directions.
→ Longitudinal Wave: Those seismic waves which vibrate in the same direction as the wave travels, just like sound waves, and the vibration of their molecules takes place to or fro in the direction of their travel.
→ Surface Wave: That seismic waves which travels along the surface of the earth.
→ Artificial Earthquakes: Earthquakes which originate due to man-made activities.
→ Isostatic Earthquakes: Such earthquakes which originate due to distortion in the balancing process of the earth’s surface.
→ Plutonic Earthquakes: Earthquakes which originate in extreme depth inside the earth are known as plutonic earthquakes.
→ Continent: An extended land part is known as continent. Generally, it is marked by naturally separating physical boundaries.
→ Transform Faults: A special type of fault which determines the boundary between two moving plates.
→ Dormant Volcano: Such volcanoes which remain inactive for some time and then erupt again are known as dormant volcanoes.
→ Extinct Volcano: Those volcanoes which have not erupted for a significant time period are known as extinct volcanoes.
→ Peninsula: That part of a continent or mainland which extends towards the reservoir or sea and is surrounded by water from three or most of the sides.
→ Cultural Landscape: Landform or landscape which originates due to the change in natural conditions effected by mankind.