Geophysical phenomena

• Urban floods
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• Indian urban landscape is undergoing a rapid transformation owing to mega urban schemes viz. Smart Cities Mission, Atal Mission for Rejuvenation and Urban Transformation (AMRUT) and Housing for All.
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• cities and towns ‐ high concentrations of people and infrastructure; vulnerabilities based on geographical location and climatic conditions, ranging frequent flooding and water logging to heat and cold waves, sea level rise, and storm surges.
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• According to National Institute of Disaster Management, floods are the most recurrent of all disasters. The Ministry of Home Affairs has identified 23 of the 35 Indian states as floodprone. India loses a little over $7 billion to floods every year, according to a United Nations report.
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• National Disaster Management Authority (NDMA) distinguishes urban floods from riverine floods as the cause of each is different and each needs a different control strategy. The common thread that connects various urban flooding incidences is “poor Urban Planning”.
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• The various factors which leads to urban flood :
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• • Inefficient drainage systems and poor planning, particularly in the country’s overcrowded metropolises (Mumbai, Chennai, Bengaluru etc.)
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• • Ever‐growing population squeezing into cities such as Mumbai and Bengaluru, which depletes natural flood barriers like wetlands; new buildings frequently rise over storm drains
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• • Climate change and resultant extreme events‐ The urban heat island effect and global climate change has resulted in episodes of high intensity rainfall events occurring in shorter periods of time. For example, the average rainfall for kerala.
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• • Increasing population leads to increased waste and the urban water bodies turn into dumping grounds for municipal solid waste, as is the case with Chennai’s Pallikaranai marshland.
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• • Encroachment of water bodies‐ for example of the 262 lakes recorded in Bengaluru in the 1960s, only ten have water at present.
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• • Storm surges can also affect coastal cities/ towns.
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• • Sudden release or failure to release water from dams can also have severe impact. Coastal cities are also facing threat from sea‐level rise.
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• develop resilient cities as per report prepared by the World Bank on “urbanization in South Asia” which enlist 4 recommendations for the same:
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• • Identify risk by using urban risk assessment framework (Urban risk assessments aim to identify critical infrastructure and develop early warning systems.)
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• • Mitigate risk by planning critical and multipurpose safe and resilient infrastructure (Mitigating risks call for developing both structural and non‐structural measures. While structural measures include dams, wave barriers and retrofitting of buildings etc., the non‐structural measures comprise policies and laws, practices, and agreements such as building codes, land‐use planning, public awareness and information.)
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• • Develop a risk financing scheme to provide immediate liquidity in the aftermath of disasters and to build financial resilience
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• • Build strong institutions and collect, share, and distribute disaster data.
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• It is also important to identify the vulnerabilities of communities and potential exposure to disasters.
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• As the government embarks upon developing infrastructure across cities, it should take care to build the transport, water, sanitation and power infrastructure with optimum physical resilience.
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• Also, since many cities are densely populated, it is not realistic to relocate millions of people away from their homes and jobs. Hence, cities should revisit urban design and ensure enforcement of building codes and land‐use plans to minimise or prevent further building in risk‐prone areas and to reinforce structures so that they are resilient to various hazards.
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• Smart city as outlined by the government includes “making Areas less vulnerable to disasters” which is a step in the right direction. Substandard construction practices should be stopped.
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• The government‐appointed Parliamentary Standing Committee formed after the Chennai floods demanded strict action against encroachments, improve drainage networks and develop vulnerability indices by creating a calamity map.
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• Flood:
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• According to the National Flood Commission of India over 40 per cent of Assam is flood‐prone. Various factors for flood in Bhramaputra valley Geographic Factors
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• • Brahmaputra is the fourth largest river in terms of flow and has multiple tributaries in the region.
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• • The region has high annual rainfall.
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• • The valley topography consists of elongated narrow plain bounded by hills in the north, east and south.
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• • Presence of low lying inhabited river islands (e.g. Mazuli island)
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• • Steep slope of hills causing frequent course change of tributaries.
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• • High silting ‐ huge deposits of silt causes Brahmaputra‘s bed to rise. This leads to a highly braided river which shifts its channel frequently.
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• • Landslides, particularly in Arunachal Pradesh from where come down most of the Brahmaputra‘s major tributaries adds to the sediment load.
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• • Climate change and extreme rainfall events: the above normal rainfall in upper Assam and Arunachal Pradesh is aggravating the problem of floods.
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• Anthropogenic Factors:
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• • Settlements in low lying areas aggravated by inward migration from porous borders.
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• • Environmental Degradation: Deforestation in Assam and its neighbouring states.
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• • Lack of Effective Administrative Measures for Flood Control: Despite the setting up of various Flood Management Committees and bodies such as the Central Water Commission in 1945, Brahmaputra Board in 1980, Ganga Flood Control Mission in 1972 and the National Disaster State Management Authority in 2005, an effective flood control strategy remains unclear.
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• • Programmes such as Flood Early Warning system seem to have been ineffective in securing the response to floods.
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• Mitigating measures:
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• 1. Afforestation and discouraging agricultural practices like Jhum.
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• 2. Mandatory EIA to prevent unsound infrastructure activities in the upper reaches.
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• 3. Removal of encroachment from river channels and depopulating the flood plains.
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• 4. Construction of reservoirs; better management of embankments through community participation.
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• 5. Advanced hydrological data sharing between China and
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• India may help in better flood preparedness.
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• 6. Use of technology like GIS for flood plain mapping and analysing and collecting data.
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• 7. Flood control in Brahmaputra valley is a key to development of North East.
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• EarthQuake
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• 1. Body waves

   

• • generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. There are two types of body waves.
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• P‐waves/Primary waves
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• • They move faster and are the first to arrive at the surface.
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• • The P‐waves are similar to sound waves.
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• • They vibrate parallel to the direction of the wave.
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• • They travel through gaseous, liquid and solid materials.
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• S‐waves/Secondary waves
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• • They arrive at the surface with some time lag.
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• • They vibrate perpendicular to the direction of propagation.
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• • They can travel only through solid materials.
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• 2. Surface waves
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• • The body waves interact with the surface rocks and generate new set of waves called surface waves. These waves move along the surface.
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• • These are the last to report on seismograph.
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• • They vibrate perpendicular to the direction of propagation.
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• • These waves are more destructive. They cause displacement of rocks, and hence, the collapse of structures occurs.
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• • Surface waves in earthquakes can be divided into two types. The first is called a Love wave. Its motion is essentially that of S waves that have no vertical displacement; it moves the ground from side to side in a horizontal plane but at right angles to the direction of propagation.
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• • The second type of surface wave is known as a Rayleigh wave. It can move both vertically and horizontally in a vertical plane pointed in the direction in which the waves are travelling.
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• Shadow Zone
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• While recording earthquake waves in seismographs, there exists some specific areas on Earth where the waves are not reported, such a zone is called the ‘shadow zone’.
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• • The entire zone beyond 105° from epicenter does not receive S‐waves which is the shadow zone for S waves
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• • The shadow zone of P‐waves appears as a band around the earth between 105° and 145° away from the epicenter
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• (as shown in the figure below).
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• • The shadow zone of S‐wave is much larger than that of the P‐waves.
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• Volcano
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• Molten magma‐ 2 types ‐ on basis of composition of silica.
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• • Basic magma or basaltic lava ‐ less in silica, mobile quiet Eruptions
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• • Acidic magma or andesitic lava , higher silica, viscous, early solidification, violent eruptions.

    

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• The gaseous constituent of ejected matters relates to the intensity of ejection. Type of volcanoes ‐ depends upon the way lava gets ejected through the vent, the composition of lava material plays predominant role.
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• 1. Shield Volcanoes‐ less steep, made up of very fluid, basaltic lava. ex. Hawaiian volcanoes
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• 2. Composite volcanoes‐ viscous, cooler lava with pyroclastic materials & ashes. accumulates in the vicinity of the vent openings leading to formation of layers.
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• 3. Caldera‐ explosive due to trapped gasses ‐ tend to collapse on themselves on erupting ‐ no structure
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• 4. Flood Basalt Provinces‐ outpour highly fluid lava ‐ flows long distance forming sheets of lava. Ex ‐ Deccan trap
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• Intrusive Volcanic landforms‐ lava cools in the crust itself is called plutonic rocks and they assume different forms. These forms are called intrusive forms.
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• • Batholiths‐ large domes ‐large magmatic material at deeper depth of the crust‐ large area, depth (upto km )
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• • Lacoliths‐ large dome‐shaped‐ with a level base ‐ connected by a pipelike conduit from below, deeper depth.
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• • Lapolith, Phacolith and sills‐ While moving upwards, a portion of the lava may tend to move in a horizontal direction wherever it finds a weak plane. It develops into a saucer shape, concave to the sky body, it is called lapolith. A wavy mass of intrusive form are phacoliths. The near horizontal bodies of the intrusive igneous rocks are called sill.
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• • Dykes‐ When lava makes its way through cracks and the fissures developed in the land. It solidifies almost perpendicular to the ground. It gets cooled to develop a wall like structure called dykes.
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• Volcanism ‐ an agent of planetary out‐gassing ‐ major contributor to initial development of earth’s atmosphere.
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• • released essential gasses such as water vapor, carbon dioxide, methane, ammonia and very little free oxygen from the interior of the earth through a process called degassing.
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• • injected ash and sulphur‐rich aerosol clouds into the atmosphere which shaded sunlight and reduced the amount of solar radiation reaching the Earth's surface thus cooling the planet.
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• • As the earth cooled, water vapor condensed to form rain dissolving carbon dioxide and other gases.
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• Some researchers also suggest that submarine volcanoes, produced a reducing mixture of gases and lavas, effectively scrubbing oxygen from the atmosphere, binding it into oxygen containing minerals.
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• However, when terrestrial volcanoes increased, the overall quantity of oxygen in the atmosphere increased. These processes continued for sometime resulting in the composition of atmosphere as what we see today with minor variation owing to anthropogenic and other natural causes.
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• Volcanic eruptions and climate change:

  

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• • Pour sulfur dioxide and other particles into the stratosphere. Gases react with water to form aerosols that linger in the stratosphere, reflecting sunlight and heat from the sun and thus lowering temperatures in the troposphere, and changing atmospheric circulation patterns.
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• • The sulphur‐rich aerosols particles also contribute to an accelerated rate of ozone depletion.
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• • For Example: A large volcanic eruption such as the Pinatubo eruption in 1991 can have a global cooling effect of 0.1°–0.3°C for several years.
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• • Intense volcanism has significantly increased the amount of carbon dioxide in the atmosphere and causes global warming. Volcanic eruptions produce more than 100 million tons CO2 each year. For Example: The 1980 eruption of Mount St. Helens vented approximately 10 million tons of CO2 into the atmosphere in only 9 hours.
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• • Dark lava flow absorbs more of the solar energy, so a large enough lava flow could warm a local region.
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• Thus volcanoes can have both a cooling and warming effect on climate. However, in the long term frequent volcanic eruptions will have a net effect of cooling the earth and counter global warming.
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• Pacific Ring of Fire
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• The Pacific Ring of Fire is the circum‐ Pacific region where greatest concentration of volcanoes in the world is found. The belt is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements.
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• Earthquakes : roughly 90% of the world’s earthquakes occur.
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• Tsunami: frequent in the coastal areas of countries.
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• Volcanoes: 75% of the active and dormant volcanoes, Islands:
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• archipelagoes like Philippines originated due to volcanic activities in the region.
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• Oceanic Deep: Along the faults, the tectonic plates form convergent boundaries between oceanic and continental plates. This results in formation of numerous deep trenches in the region.
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• Comparison of Volcanoes in Atlantic and Pacific Ocean
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• While the pacific coasts have this high concentration of volcanoes, Atlantic coasts have comparatively few active volcanoes. The reason for this is that pacific ring of fire has comparatively higher divergent plate activity which leads to volcanoes being active as the plates actively grind against each other.
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• Landslides
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• Landslides are among the major hydro‐geological hazards that affect large parts of India viz. The Himalayas (tectonically unstable), the Northeastern hill ranges, the Western Ghats, the Nilgiris, the Eastern Ghats and the Vindhyas, in that order, covering about 15 % of the landmass.
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• Climate change leads to change in rainfall pattern and increased extreme events. Change in rainfall and evapotranspiration directly impacts the groundwater level. Landslides respond to this change in groundwater level (pore pressure).Rainfall‐induced landslides threaten settlements on unstable slopes and in landslide prone‐areas in some parts of India
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• Similarly, Climate warming leads to permafrost degradation and permafrost melting phase transition, resulting in an increasing number of landslides.
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• The trees through their roots that hold the soil in place. Loose soil on the hillside surface provides appropriate conditions for the infiltration of water (from precipitation, snowmelt). The infiltrating water is blocked by the underlying permafrost or dense soil, forming a potential sliding zone.
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• Anthropogenic factors:
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• • Slope instability due to removal of lateral and underlying support.
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• • Indiscriminate chopping down of trees.
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• • Slash and burn cultivation practices in hills like in northeast India.
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• Road construction, mining activities, dynamite blasting of rocks, earth work, constructions, vibrations from big machines
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• • With increasing population pressure, there is an increase in grazing activities, urbanization which reduces dense natural evergreen forest cover.
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• • Loosening of the soil due to these various anthropogenic activities like agriculture.
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• Methods to control of landslide
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• • Community farming‐ fuel or fodder trees should be grown to increase forest cover to reduce landslide hazard.
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• • Grazing should be restricted and better grass must be grown on the surface previously grazed to increase the hold on soil by plant roots. These grasses can be of some commercial importance so that economic returns encourage farmers in areas prone to landslide in India.
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• • The runoff collection ponds in the catchment areas must be dug to store water.
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• • Appropriate building codes, safety regulations, and response plans
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• • Landslide Hazard Zonation (LHZ) mapping is useful in identifying potential risk areas where landslides may occur repeatedly. NDMA Guidelines are useful in this regard.
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• Tsunami
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• • Earthquakes, landslides and volcanic eruptions cause the sea‐floor to move abruptly resulting in sudden displacement of ocean water in the form of high vertical waves.
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• • after the initial disturbance, a series of afterwaves are created in the water that oscillate between high crest and low trough in order to restore the water level.
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• Propagation of Tsunami
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• • The speed of wave in the ocean depends upon the depth of water. more in the shallow water than in the ocean deep.
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• • impact of tsunami is less over the ocean and more near the coast where they cause large‐scale devastations.
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• • in deep water the tsunami has very long wave‐length and limited wave‐height. Thus, a tsunami wave raises a ship only a metre or two and each rise and fall takes several minutes.
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• • when a tsunami enters shallow water, its wave‐length gets reduced and the period remains unchanged, which increases the height of the wave. Sometimes, this height can be up to 15m+, which causes large‐scale destructions along the shores.
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• Effects of Tsunami
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• • Sea Floor Erosion: The base of a tsunami wave can change the topography of the sea floor. It erodes seafloor sediments and can devastate the benthic – sea bottom – ecosystems on the sea floor. The March 2011 Tohoku, Japan, earthquake tsunami deposited the eroded sediments in other locations as huge seafloor sand dunes.
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• • Coral Reefs: The December 2004 Indonesian earthquake tsunami devastated coral reefs around Indian Ocean coastlines.
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• • Intertidal environments: Sea grass beds, mangrove forests, coastal wetlands and their associated fish and animal life in the intertidal zone are particularly vulnerable to tsunamis.

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• • Species Invasion: Tsunamis can carry massive amounts of debris from one side of the ocean to another. Algae and other organisms attached to this debris survived the ocean crossing. These can establish new communities in Oregon and potentially displace native species.
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• • Contamination of soil and water: The 2004 Tsunami led to Salivation of water bodies such as rivers, lakes, wells in many of the effected countries
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• Conclusion: mitigated by healthy well maintained coral reefs, mangroves, sand dunes and other coastal systems such as peat swamp.