CBSE Class 8 Social Science Disaster Management Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.
• Earthquake : An earthquake is a sudden release of energy accumulated in deformed rocks which causes the ground to tremble or shake.
• Seismograph : It is an instrument which measures and records vibrations of an earthquake.
• Richter Scale : Richter scale is the scale having 0 to 9 range used to measure the magnitude and intensity of an earthquake. One point increase represents 10 times magnitude of the earthquake.
• Landslides : Sliding of mass of rock, earth an debris which move down a slope of a mountain by their own force and weight are termed as landslides.
• Debris flow : Flow of debris in the Western Ghats of kerala down the slopes is called debris flow.
• Floods : Floods are temporary inundation of large areas due to an increase in reservoir or due to rivers flooding their banks because of heavy rains, cyclones etc.
• A Cyclone : A Cyclone is a violent storm, often of vast extent, characterised by high winds rotating about a calm centre of low atmospheric pressure.
• A Drought : A drought is an insidious natural hazard that results from a departure of precipitation over a season or longer period of time, insufficient of meet the demands of human, plant and animal activities.
• Watershed : Watershed is the geographic area where water flows to a common point.
8 There are several hazards.
8 Each hazard has its own characteristics.
8 We have to keep these characteristics in mind while taking steps for their mitigation.
8 Causes and effects of hazards help us to select strategies for mitigation of hazards.
• Several Types of Hazards :
Several types of hazards have widespread concern to us. For a simple understanding of hazards, we classify them as under
8 Sudden on-set Hazards : Earthquakes, tsunamis, volcanic eruptions, landslides, floods, tropical cyclones, avalanche, cloud burst etc.
8 Slow on-set Hazards : Drought, famine, environmental, degradation, pest infestation, desertification.
8 Epidemics : Water/food borne diseases, person to person diseases, vector borne diseases.
8 Industrial technological Accidents : System failures, fire, explosion, chemical leakage/spillage.
8 Wars and Civil Strifes :
The structure for common hazards and mitigation is described in the following sequence
8 On set type.
8 Hazard assessment.
8 Main mitigation strategies.
8 Elements at risk.
8 Community based mitigation
We should keep the following points in mind while taking steps to mitigate the impact of hazards :
(i) All disasters have different typical effects.
(ii) The mitigation strategies are to be taken up as per the local conditions.
(iii) Looking at multi-hazard zones in terms of possible combined effects. Example:
Heavy rains can cause floods and in certain regions it can even trigger landslides if the ground conditions are conductive to them.
(iv) The impact of the disaster depends on community preparedness, natural constraints, management and institutional mechanism.
• Definition : An earthquake is a sudden release of energy, which has accumulated in deformed rocks, causing the ground/earth to tremble or shake.
• Onset Type and Warning :
8 Earth quake onsets suddenly.
8 They occur at any time, day, night and at any time of the year.
8 They occur all of a sudden without any advanced warning.
8 Their impact is sudden.
8 Earthquakes cannot be predicted despite extensive researches and investigation in recent decades.
• Elements at Risk :
The following elements are at risk during earthquakes
1. Settlements :
8 Settlements in earthquake prone areas-built on alluvial and wind blown soil deposits.
8 Settlements built in landslide prone areas.
8 Settlements built along geological fault lines.
2. Buildings :
8 Weak and having high occupancy.
8 Traditionally built using earth, rubble, bricks by masons.
8 Buildings with heavy roofs.
8 Buildings with poor quality material.
8 Buildings with poor maintenance.
8 Buildings with weak and flexible storage.
• Typical Effects Of Earthquakes
1. Physical Damage :
8 Damage of building
8 Damage to service structure
8 Fires due to short circuit
8 Floods due to dam failures.
8 Landslides, in hilly and mountainous regions.
2. Casualties :
8 Very high near the epicentre
8 Very high in thickly populated areas.
8 In buildings. which are not earthquake resistant.
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