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Subject: Geography

  • Understanding Summer Solstice: Longest Day of the Year

    summer solstice

    Central Idea

    • The summer solstice, also known as the longest day of the year, occurs on June 21st for those living north of the Equator.
    • This article explores the significance of the summer solstice, the reasons behind its occurrence, and the effects it has on different parts of the world.

    What is Summer Solstice?

    • The summer solstice is the moment when the Earth’s axial tilt is most inclined towards the Sun.
    • It occurs annually on or around June 21st in the Northern Hemisphere.
    • During the summer solstice, the Sun follows its highest and longest path across the sky.
    • This results in an extended duration of daylight hours, making it the longest day of the year.

    Factors Influencing the Summer Solstice

    • Earth’s Axial Tilt: The Earth’s axis is tilted relative to its orbit around the Sun, at an angle of approximately 23.5 degrees.
    • Tropic of Cancer: The summer solstice takes place when the Sun is directly over the Tropic of Cancer, located at 23.5 degrees north latitude.
    • Seasonal Variations: The tilt of the Earth’s axis causes different latitudes to receive varying amounts of sunlight throughout the year.

    Sunlight Distribution in the Hemispheres

    • The Northern Hemisphere receives the maximum amount of sunlight during the summer solstice, typically on June 20, 21, or 22.
    • In contrast, the Southern Hemisphere experiences its peak sunlight during the winter solstice, which occurs on December 21, 22, or 23.

    Cultural Significance and Celebrations

    • The summer solstice holds cultural and religious significance in various civilizations throughout history.
    • Festivals and rituals often commemorate this astronomical event, symbolizing the triumph of light and fertility.
    • People around the world celebrate the summer solstice through festivals, bonfires, music, dancing, and outdoor activities.
    • Notable celebrations include the Summer Solstice Stonehenge Festival in England and the Midnight Sun Festival in Norway.

    Back2Basics: Solstices and Equinoxes

    Summer Solstice Winter Solstice Equinoxes
    Date Around June 21st Around December 21st Around March 20th and September 22nd
    Hemisphere Northern Northern Global (Equal duration of day and night)
    Day Length Longest day and shortest night Shortest day and longest night Equal day and night duration
    Sun’s Path Highest arc in the sky Lowest arc in the sky Intermediate arc in the sky
    Season Summer Winter Spring and Autumn
    Axial Tilt North Pole tilted towards the Sun South Pole tilted towards the Sun No tilt, relative to the Sun
    Daylight Hours Maximum Minimum Approximately equal
    Cultural Significance Celebrated as the triumph of light, festivals, and rituals Celebrated as the return of light, festivals, and rituals Symbolizes balance and transition, celebrated by various cultures

     

  • Places in news: Brahmani Natural Arch

    brahmani arch

    Central Idea

    • The Geological Survey of India (GSI) plans to declare the ‘Brahmani Natural Arch’ in Kanika range of Sundargarh forest division of Odisha as a Geo Heritage Site.
    • This natural arch is believed to date back to the Jurassic period and would be the largest natural arch in India with the Geo Heritage tag.

    Brahmani Natural Arch

    • The oval-shaped arch has a base length of 30 meters and a height of 12 meters.
    • The alcove of the arch has a maximum height of 7 meters and a width of 15 meters.
    • India currently has two other natural arches, located at Tirumala hills in Tirupati and Andaman and Nicobar, but both are smaller than the one in Sundargarh.

    Its formation

    • The natural arch is composed of ferruginous sandstone from the Upper Kamthi formation.
    • It dates back to the lower to middle Jurassic age, approximately 184 to 160 million years old.
    • Research on the geological significance of the site began in 2017 after its discovery during coal exploration in the district.

    Awareness and Preservation Efforts

    • The GSI state unit and Sundargarh forest division conducted an awareness drive in the district to promote the protection of the natural arch.
    • Steps are being taken to promote the proposed geo-heritage site as a cultural pride and potentially name it ‘Brahmani natural arch.’
    • The site could be promoted and preserved as an eco-tourism destination.

    Back2Basics:

    Geological Heritage Sites in India
    Andhra Pradesh Mangampeta Volcanogenic bedded Barytes (Cuddapah Dist.), Eparchaean Unconformity (Chittor Dist.), Natural Geological Arch in Tirumala Hills (Chittor Dist.), Erra Matti Dibbalu located between Vishakhapatnam and Bhimunipatnam.
    Maharashtra Lonar Lake (Buldana Dist.)
    Kerala Laterite near Angadipuram PWD rest house premises (Malapuram Dist.), Varkala Cliff Section (Thiruvanatapuram Dist.)
    Chattisgarh Lower Permian Marine bed at Manendragarh (Surguja Dist.)
    Tamil Nadu Fossil wood near Tiruvakkarai (South Arcot Dist.), National fossil wood park in Sattanur (Tiruchirapalli Dist.), Charnockite in St. Thomas Mount (Madras), Badlands of Karai Formation with Cretaceous fossils along Karai – Kulakkalnattam Section (Perambalur District)
    Karnataka Columnar Lava in St. Mary Island (Udupi Dist.), Pillow lavas near Mardihalli (Chitradurga Dist.), Peninsular Gneiss in Lalbagh (Bangalore), Pyroclastics & Pillow lavas in Kolar Gold fields (Kolar Dist.)
    Gujarat Sedimentary Structures – Eddy Markings in Kadan Dam (Panch Mahals Dist.)
    Himachal Pradesh Siwalik Fossil Park (Saketi, Sirmur dt.)
    Rajasthan Sendra Granite (Pali Dist.), Barr Conglomerate (Pali Dist.), Stromatolite Fossil Park near Jharmarkotra Rock Phosphate deposit (Udaipur Dist.), Gossan in Rajpura-Dariba Mineralised belt (Udaipur Dist.), Akal Fossil Wood Park (Jaisalmer Dist.)
    Odisha Pillow Lava in iron ore belt at Nomira (Keonjhar dist.)
    Jharkhand Plant Fossil bearing Inter-trappean beds of Rajmahal Formation around Mandro (Sahibganj dist.)
    Nagaland Nagahill Ophiolite Site near Pungro
    Sikkim Stromatolite bearing Dolomite/Limestone of Buxa Formation at Mamley, near Namchi (South district), Stromatolite bearing Dolomite / Limestone of Buxa Formation, Sikkim

     

     

    https://www.newindianexpress.com/cities/bhubaneswar/2023/jun/11/gsi-proposes-geo-heritage-tag-for-jurassic-age-natural-arch-in-odisha-2583901.html

  • Monsoon onset in Kerala on June 4

    monsoon

    Central Idea: The monsoon is likely to set in over Kerala with a “slight delay” on June 4, the India Meteorological Department (IMD) said. The usual onset date over Kerala is June 1, within a seven-day window.

    What does the “Onset of Monsoon” mean?

    • The onset of the monsoon over Kerala marks the beginning of the four-month, June to September southwest monsoon season over India.
    • It brings more than 70 per cent of the country’s annual rainfall.
    • It marks a significant transition in the large-scale atmospheric and ocean circulations in the Indo-Pacific region.
    • The IMD announces it only after certain newly defined and measurable parameters, adopted in 2016, are met.
    • The onset is a significant day in India’s economic calendar.

    How does IMD predict the monsoon?

    • Broadly, the IMD checks for the consistency of rainfall over a defined geography, its intensity, and wind speed:
    1. Rainfall: The IMD declares the onset of the monsoon if at least 60% of 14 designated meteorological stations in Kerala and Lakshadweep record at least 2.5 mm of rain for two consecutive days at any time after May 10.
    2. Wind field: The depth of westerlies should be upto 600 hectopascal (1 hPa is equal to 1 millibar of pressure) in the area bound by the equator to 10ºN latitude, and from longitude 55ºE to 80ºE. The zonal wind speed over the area bound by 5-10ºN latitude and 70-80ºE longitude should be of the order of 15-20 knots (28-37 kph) at 925 hPa.
    3. Heat: The INSAT-derived Outgoing Longwave Radiation (OLR) value (a measure of the energy emitted to space by the Earth’s surface, oceans, and atmosphere) should be below 200 watt per sq m (wm2) in the box confined by 5-10ºN latitude and 70-75ºE latitude.
    • The onset is not officially declared until the prescribed conditions (above) are met.

    Factors considered by IMD

    • The IMD uses a specialised model that forecasts the arrival dates within a four-day window.
    • It uses six predictors:
    1. Minimum temperatures over northwest India
    2. Pre-monsoon rainfall peak over south Peninsula
    3. Outgoing long-wave radiation (OLR) over the South China Sea
    4. Lower tropospheric zonal wind over the southeast Indian Ocean
    5. Upper tropospheric zonal wind over the east equatorial Indian Ocean, and
    6. OLR over the southwest Pacific region

    Back2Basics: Long Period Average (LPA)

    • The IMD predicts a “normal”, “below normal”, or “above normal” monsoon in relation to a benchmark “long period average” (LPA).
    • The LPA of rainfall is the rainfall recorded over a particular region for a given interval (like month or season) average over a long period like 30 years, 50 years, etc.
    • LPA refers to the average rainfall recorded from June to September for the entire country, the amount of rain that falls every year varies from region to region and from month to month.
    • The IMD’s prediction of a normal monsoon is based on the LPA of the 1971-2020 period, during which India received 87 cm of rain for the entire country on average.
    • It has in the past calculated the LPA at 88 cm for the 1961-2010 period, and at 89 cm for the period 1951-2000.

    Why LPA is needed?

    • The IMD records rainfall data at more than 2,400 locations and 3,500 rain-gauge stations.
    • Because annual rainfall can vary greatly not just from region to region and from month to month, but also from year to year within a particular region or month.
    • An LPA is needed to smooth out trends so that a reasonably accurate prediction can be made.
    • A 50-year LPA covers for large variations in either direction caused by freak years of unusually high or low rainfall, as well as for the periodic drought years.
    • It also takes into account the increasingly common extreme weather events caused by climate change.

    Range of normal rainfall

    The IMD maintains five rainfall distribution categories on an all-India scale. These are:

    1. Normal or near normal, when the percentage departure of actual rainfall is +/-10% of LPA, that is, between 96-104% of LPA;
    2. Below normal, when departure of actual rainfall is less than 10% of LPA, that is 90-96% of LPA;
    3. Above normal, when actual rainfall is 104-110% of LPA;
    4. Deficient, when departure of actual rainfall is less than 90% of LPA; and
    5. Excess, when the departure of actual rainfall is more than 110% of LPA.

     

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  • Palghat Gap: A break in the Western Ghats

    palghat

    Central Idea: The article discusses the Palghat (Palakkad) Gap, a significant corridor in the Western Ghats of India. It provides information about the geological origin of the gap.

    What is Palghat Gap?

    • The Palghat Gap is a 40 km wide corridor in the Western Ghats, known for its steep hills and serving as a gateway to Kerala.
    • It is a crucial passage for roads and railways connecting Coimbatore and Palakkad.
    • The Bharathappuzha River flows through the Palghat Gap.
    • The vegetation in the gap is classified as dry evergreen forest, different from the tropical rainforests of the Western Ghats.
    • The Palghat Gap marks a distinct divide in the flora and fauna of the region.

    Geological origin of the Palghat Gap

    • The Palghat Gap is a geological shear zone running from east to west.
    • Shear zones are weak regions in the Earth’s crust, occasionally causing tremors in the Coimbatore region.
    • The formation of the Palghat Gap occurred when the continental shelves shifted after the separation of Australia and Africa from the Gondwana landmass.
    • India and Madagascar were connected until volcanic activity led to their split, with a similar gap called the Ranotsara Gap in Madagascar.

    Biogeographic distinctions and ancient history

    • The biogeographic distinctions in species north and south of the Palghat Gap may be attributed to an ancient river or an incursion of the sea in the distant past.
    • Elephant populations on the Nilgiris side of the gap have different mitochondrial DNA from elephants in the Anamalai and Periyar sanctuaries.
    • DNA analysis of the White-bellied Shortwing, an endemic bird species, shows divergence between populations in the Nilgiris and the Anamalai regions.

    Biodiversity south of the Palghat Gap

    • The southern region of the Western Ghats, located south of the Palghat Gap, exhibits high species richness and phylogenetic diversity.
    • A recent study reports over 450 tree species, including ancient species like Magnolia champaca, dating back 130 million years.
    • The warm weather and moist air of the southern Western Ghats support a diverse range of life, making it an island refuge during cycles of ice ages and droughts.
    • The southern Western Ghats receive rainfall more evenly throughout the year compared to the northern region.

    Back2Basics: Western Ghats

    • The Western Ghats, also known as the Sahyadri mountain range, is a UNESCO World Heritage Site and one of the 36 biodiversity hotspots in the world.
    • It spans an area of 160,000 sq. km. and stretches for 1,600 km parallel to the western coast of the Indian peninsula, passing through the states of Gujarat, Maharashtra, Goa, Karnataka, Kerala, and Tamil Nadu.
    Description
    Flora and Fauna The Western Ghats are home to a rich diversity of flora and fauna, including over 7,402 species of flowering plants, 1,814 species of non-flowering plants, 139 mammal species, 508 bird species, 227 reptile species, 179 amphibian species, 290 freshwater fish species, and 6,000 insect species.
    Geological Significance The Western Ghats, known as the “Great Escarpment of India,” are older than the Himalayas. They influence India’s monsoon weather patterns by intercepting rain-laden monsoon winds from the southwest during late summer.
    Geographic Features Stretching north to south along the western edge of the Deccan Plateau, the Western Ghats separate the plateau from the narrow coastal plain called the Western Coastal Plains, which lies along the Arabian Sea.
    Catchment Area The Western Ghats cover a vast catchment area for complex riverine drainage systems, contributing to almost 40% of India’s total drainage. The range acts as a barrier, blocking southwest monsoon winds from reaching the Deccan Plateau.

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  • Over 19,000 Seamounts discovered

    seamount

    Central Idea: Scientists have reported finding 19,325 new seamounts after poring through new high-resolution data. A study had already mapped 24,000 seamounts across the world’s oceans.

    Why study this?

    • The recent discovery of new seamounts was made possible by advancements in altimetry for gravity-field mapping, which improved spatial coverage.
    • The CryoSat-2, Envisat, Jason-1 geodetic missions, and the SARAL satellite developed by India and France contributed to these advancements.

    What are Seamounts?

    • Seamounts are underwater mountains formed through volcanic activity.
    • They are recognised as hotspots for marine life.
    • Most seamounts are formed near mid-ocean ridges, intraplate hotspots, and oceanic island chains with volcanic and seismic activity called island arcs.
    • They can be active, extinct or dormant volcanoes.

    Importance of Seamounts

    • Seamounts provide information about the mantle’s composition and how tectonic plates evolve as they are formed when molten rock comes up from below the tectonic plates.
    • Oceanographers study seamounts to understand their influence on how water circulates and absorbs heat and carbon dioxide.
    • Seamounts are home to diverse biological communities as they can cause localised ocean upwelling, which brings nutrient-rich water from deep within the ocean to the surface.

    How were they mapped?

    • Surveyors map seamounts using either echo sounders or multibeam sonar on ships for topographic mapping or using satellite altimetry for gravity-field mapping.
    • The hi-res maps produced by multibeam sonar mapping are often incomplete, whereas the low-res maps produced by satellite altimetry have better coverage.

     

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  • What is Ningaloo ‘Hybrid’ Solar Eclipse?

    ningaloo

    A ‘hybrid’ solar eclipse called the Ningaloo Eclipse recently happened on April 20, 2023.

    Ningaloo ‘Hybrid’ Solar Eclipse

    • It was a rare astronomical event that occurred on April 20, 2023.
    • The Moon passed directly between the Sun and the Earth, casting a shadow on a narrow strip of land in Western Australia.
    • It was a “hybrid” eclipse, starting as an annular eclipse and transitioning into a total eclipse.
    • The path of the eclipse crossed over the Ningaloo Reef, a world heritage site in Western Australia.
    • It offered a unique opportunity to view the eclipse against the backdrop of the reef and the Indian Ocean.

    How rare are such events?

    • During a solar eclipse, the Moon passes between the Sun and Earth, casting a shadow on Earth’s surface.
    • However, solar eclipses do not occur every month because the Moon’s orbit is tilted by about 5 degrees relative to Earth’s orbit around the Sun.
    • Therefore, the Moon’s shadow usually misses Earth, but occasionally the alignment is just right for a solar eclipse to occur.
    • In the case of the Ningaloo Hybrid Solar Eclipse, the alignment was such that the Moon was at the right distance from Earth to create both an annular and a total eclipse as it moved across the Sun.
    • This type of eclipse is quite rare, occurring only about once every 400 years.

    Back2Basics:

    ningaloo

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  • Africa’s splitting plates could give birth to a new Ocean: Study

    africa

    Central idea

    • Scientists predict a new ocean will be created as Africa splits into two separate parts connected to the East African Rift
    • This geological process will inevitably divide the continent resulting in new coastlines and sub-sea internet infrastructure but also will have significant repercussions

    What is Rifting?

    • The Earth’s lithosphere, comprising the crust and upper part of the mantle, is divided into tectonic plates that move in relation to each other at varying speeds.
    • Tectonic forces move the plates and can cause them to rupture, resulting in the formation of a rift and potentially leading to the creation of new plate boundaries.
    • Rifting refers to the geological process in which a single tectonic plate is split into two or more plates separated by divergent plate boundaries.
    • In the present day, the gradual separation of the Somali and Nubian tectonic plates is leading to the formation of a rift that could eventually lead to the creation of a new ocean basin.
    • The movement of tectonic plates is a fascinating geological phenomenon.

    Rifting in African Continent

    • The African continent is located on the African Plate, which is one of the Earth’s major tectonic plates.
    • The continent is characterized by a number of geological features, including rift valleys.

    Most profound feature: The East African Rift System

    • The East African Rift System is the most prominent example of rifting in Africa.
    • It stretches for over 6,000 kilometers from the Red Sea in the north to the Zambezi River in the south.
    • The rift system includes a series of interconnected rift valleys, volcanoes, and lakes.

    Causes of the East African Rift System

    • The rift system is caused by the movement of the African Plate away from the Arabian Plate and the Somalian Plate.
    • This movement creates tension in the Earth’s crust, causing it to pull apart and form a rift.

    Impact: Lakes Formed by Rifting

    • Over time, the rifting process has led to the formation of several large lakes in the region.
    • These lakes include Lake Victoria, Lake Tanganyika, and Lake Malawi.
    • They are believed to have formed as a result of the sinking of the land between the rift valleys.

    Future of Rifting in Africa

    • The rifting process is ongoing and may eventually lead to the splitting of the African continent into two or more separate land masses.
    • However, this process is expected to take millions of years and is not likely to have a significant impact on human populations in the near future.
    • The necessary evacuation of people and potential loss of lives will be an unfortunate cost of this natural phenomenon.
    • The emergence of new coastlines will unlock opportunities for economic growth
    • As the plates continue to split in the future, this phenomenon will result in the displacement of communities, settlements, and various flora and fauna.

    Conclusion

    • The movement of tectonic plates has significant implications for the continent’s future.
    • It is important to study and monitor these changes while remembering the power of the Earth’s natural forces and the impact they can have over time.
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  • States demand that ‘Lightning’ be declared a Natural Disaster

    Central idea: A few states have requested lightning to be declared a natural disaster due to the high number of deaths caused by it in the country.

    Why discuss this?

    • Around 2,500 people die every year due to lightning.
    • Present norms consider cyclones, droughts, earthquakes, fires, floods, tsunamis, hailstorms, landslides, avalanches, cloudbursts, pest attacks, frost, and cold waves as disasters covered under the State Disaster Response Fund.
    • Deliberations are necessary as it is a policy issue.

    What is lightning?

    • Scientifically, lightning is a rapid and massive discharge of electricity in the atmosphere some of which is directed towards earth.
    • The discharges are generated in giant moisture-bearing clouds that are 10-12 km tall.
    • The base of these clouds typically lie within 1-2 km of the Earth’s surface, while the top is 12-13 km away.
    • Temperatures in the top of these clouds are in the range of –35° to –45°C.

    Its formation

    • As water vapour moves upward in the cloud, the falling temperature causes it to condense.
    • As they move to temperatures below 0°C, the water droplets change into small ice crystals.
    • They continue to move up, gathering mass until they are so heavy that they start to fall to Earth.
    • This leads to a system in which, simultaneously, smaller ice crystals are moving up and bigger crystals are coming down.
    • Collisions follow and trigger the release of electrons, a process that is very similar to the generation of sparks of electricity.
    • As the moving free electrons cause more collisions and more electrons, a chain reaction ensues.
    • This process results in a situation in which the top layer of the cloud gets positively charged, while the middle layer is negatively charged.
    • The electrical potential difference between the two layers is huge, of the order of a billion to 10 billion volts.
    • In very little time, a massive current, of the order of 100,000 to a million amperes, starts to flow between the layers.

    Types of lightning

    • Broadly, there are three forms of lightning:
    1. Inter-cloud
    2. Intra-cloud
    3. Cloud-to-ground
    • It is the cloud-to-ground form of lightning that kills humans, as well as animals and livestock, and can substantially damage property.
    • While the Earth is a good conductor of electricity, it is electrically neutral.
    • However, in comparison to the middle layer of the cloud, it becomes positively charged.
    • As a result, about 15%-20% of the current gets directed towards the Earth as well.
    • It is this flow of current that results in damage to life and property on Earth.

    How intensely does it strike?

    • A typical lightning flash is about 300 million volts and30,000 amps.
    • To put it in perspective, household current is 120 volts and 15 amps.
    • A flash of lightning is enough to light a 100-watt incandescent bulb for about three months.

    Why does lightning kill so many people in India?

    • The reason for the high number of deaths is due to people being caught unawares and more than 70% of fatalities happened due to people standing under isolated tall trees.
    • About 25 per cent of the people were struck in the open.
    • Also, lightning is the direct promulgation of climate change extremities.

    Mitigating lightning incidents

    • Lightning is not classified as a natural disaster in India.
    • But recent efforts have resulted in the setting up of an early warning system that is already saving many lives.
    • More than 96% of lightning deaths happen in rural areas.
    • As such, most of the mitigation and public awareness programmes need to focus on these communities.
    • Lightning protection devices are fairly unsophisticated and low-cost. Yet, their deployment in the rural areas, as of now, is extremely low.
    • States are being encouraged to prepare and implement lightning action plans, on the lines of heat action plans.
    • An international centre for excellence on lightning research to boost detection and early warning systems is also in the process of being set up.

  • ISRO releases Landslide Atlas of India

    landslide

    The Indian Space Research Organisation (ISRO) recently released the Landslide Atlas of India to identify landslide hotspots in the country.

    What are Landslides?

    • Landslides are natural disasters that occur in mountainous terrains where soil, rock, geology, and slope conditions are conducive.
    • A landslide is the sudden movement of rock, boulders, earth, or debris down a slope.
    • They can be triggered by natural causes such as heavy rainfall, earthquakes, snowmelting, and undercutting of slopes due to flooding.
    • They are extremely hazardous, posing a threat to human and animal lives, damaging property, roads, and bridges, disrupting communication lines, and snapping power lines.
    • Landslides are broadly classified based on the type of materials involved, the type of movement of the material, and the type of flow of the material.

    Why do they occur?

    • Landslides are natural disasters that occur mainly in mountainous terrains due to conducive conditions of soil, rock, geology, and slope.
    • Heavy rainfall, earthquakes, snow-melting, and undercutting of slopes due to flooding can trigger landslides.
    • Anthropogenic activities such as excavation, cutting of hills and trees, excessive infrastructure development, and overgrazing by cattle can also cause landslides.

    Factors contributing

    • The main factors that influence landslides include lithology, geological structures like faults, hill slopes, drainage, geomorphology, land use and land cover, soil texture and depth, and weathering of rocks.
    • Rainfall variability pattern is the single biggest cause for landslides in India, with the Himalayas and the Western Ghats remaining highly vulnerable.

    India’s vulnerability to landslides

    • India is considered among the top five landslide-prone countries globally, where at least one death per 100 sq. km is reported in a year due to a landslide event.
    • Approximately 12.6% of the country’s geographical land area (0.42 million sq km) is prone to landslides, with 66.5% of landslides reported from the North-western Himalayas, 18.8% from the North-eastern Himalayas, and 14.7% from the Western Ghats.

    Risks in specific states          

    • Mizoram recorded the highest number of landslide events in the past 25 years, with 12,385 events, of which 8,926 were recorded in 2017 alone.
    • Nagaland and Manipur also reported a high number of landslide events during the 2017 monsoon season.
    • Uttarakhand and Kerala reported the highest number of landslides, with Uttarakhand experiencing 11,219 events since 1998, and Kerala making inhabitants significantly vulnerable to fatalities, despite fewer events.

    Classification and Mapping of Landslides

    • Landslides are broadly classified based on the type of materials involved, type of movement, type of flow of the material, and whether they spread laterally.
    • The Landslide Atlas of India maps landslides mainly based on events and seasons.
    • The National Remote Sensing Centre (NRSC) used a landslide database created from 1998 to 2022 using aerial and high-resolution satellite images.

     

  • Turkey hit by series of powerful Earthquakes: The science behind it

    turkey

    More than 4000 people died and several hundred were injured after a major earthquake of magnitude 7.8 hit south-central Turkey and Northwest Syria.

    What is an Earthquake?

    • An earthquake is an intense shaking of the ground caused by movement under the earth’s surface.
    • It happens when two blocks of the earth suddenly slip past one another.
    • This releases stored-up ‘elastic strain’ energy in the form of seismic waves, which spreads through the earth and cause the shaking of the ground.

    What exactly causes Earthquakes?

    • As we know, the earth’s outermost surface, crust, is fragmented into tectonic plates.
    • The edges of the plates are called plate boundaries, which are made up of faults.
    • The tectonic plates constantly move at a slow pace, sliding past one another and bumping into each other.
    • As the edges of the plates are quite rough, they get stuck with one another while the rest of the plate keeps moving.
    • Earthquake occurs when the plate has moved far enough and the edges unstick on one of the faults.
    • The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicentre.

    How prone is Turkey to Earthquakes?

    • Turkey and Syria lie in a seismically active region
    • The region where the earthquake has struck lies along a well-known seismic fault line called the Anatolia tectonic block that runs through northern, central, and eastern Turkey.
    • It is a seismically active zone — though not as active as, say, the Himalayan region which is one of the most dangerous regions in the world from the perspective of earthquakes.

    What makes Turkey a hotbed of seismic activity?

    turkey

    • Turkey is frequently shaken by earthquakes. In 2020 itself, it recorded almost 33,000 earthquakes in the region.
    • Turkey is located on the Anatolian tectonic plate, which is wedged between the Eurasian and African plates.
    • On the north side, the minor Arabian plate further restricts movement.
    • One fault line — the North Anatolian fault (NAF) line, the meeting point of the Eurasian and Anatolian tectonic plates — is known to be “particularly devastating”.
    • Then there is the East Anatolian fault line, the tectonic boundary between the Anatolian Plate and the northward-moving Arabian Plate.
    • It runs 650 kilometers from eastern Turkey and into the Mediterranean.
    • In addition to this, the Aegean Sea Plate, located in the eastern Mediterranean Sea under southern Greece and western Turkey, is also a source of seismic activity in the region.

    Where was the earthquake epicentered?

    • The centre of the earthquake was centred about 33 km from Gaziantep, around 18 km deep.
    • Its effect was felt across West Asia, Northern Africa and South Eastern Europe with residents of Lebanon, Cyprus, Greece, Israel and Egypt also reporting tremors.

    Aftermath: Many Aftershocks hits the region

    • Aftershocks are a sequence of earthquakes that happen after a larger mainshock on a fault.
    • Aftershocks occur near the fault zone where the mainshock rupture occurred and are part of the “readjustment process” after the main slip on the fault.
    • While they become less frequent with time, although they can continue for days, weeks, months, or even years for a very large mainshock.

    Can earthquakes be predicted?

    • An accurate prediction of an earthquake requires some sort of a precursory signal from within the earth that indicates a big quake is on the way.
    • Moreover, the signal must occur only before large earthquakes so that it doesn’t indicate every small movement within the earth’s surface.
    • Currently, there is no equipment to find such precursors, even if they exist.

    India offers assistance

    • India is among the 45 countries, which have so far offered assistance to Turkey.
    • It’s sending search and rescue teams of the National Disaster Relief Force (NDRF) and medical teams along with relief material to the West Asian nation.