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GS Paper: GS1-15.Geographical features and their location- Changes in critical geographical features (including water-bodies and ice-caps) and in flora and fauna and the effects of such changes.

  • Gravity Hole in the Indian Ocean

    gravity hole
    The true shape of our Earth

    Central Idea

    • One intriguing phenomenon recently discovered is the presence of a significant “gravity hole” in the Indian Ocean, where the gravitational pull is notably weaker.
    • Recent research sheds light on the possible causes behind this anomaly.

    What is a Gravity Hole?

    • A “gravity hole” refers to a region on Earth where the gravitational pull is significantly weaker compared to the surrounding areas or the global average.
    • It is characterized by a dip or low gravity anomaly.
    • In such areas, the sea level may be lower than average due to the weaker gravitational force acting upon the water.
    • This term is often used to describe specific locations, such as the Indian Ocean geoid low (IOGL), where the gravitational pull is notably diminished compared to nearby regions.
    • The exact causes of gravity holes can vary and may involve factors such as variations in the Earth’s mass distribution or underlying geological features.

    What is Indian Ocean Geoid Low (IOGL)?

    • It is located approximately 1,200 kilometers southwest of the southernmost tip of India.
    • IOGL is an area in the Indian Ocean where the sea level is about 106 meters below the global average.

    Unraveling the Causes of IOGL

    • Discovering the Anomaly: Geophysicist Felix Andries Vening Meinesz first identified the IOGL during a survey in 1948. Since then, it has been confirmed by subsequent ship-based experiments and satellite measurements.
    • Ancient Ocean Hypothesis: Researchers from the Indian Institute of Science conducted computer-simulated models spanning 140 million years. They discovered remnants of an ancient ocean, located approximately 965 kilometers below the Earth’s crust, just beneath Africa.
    • Molten Rock Plumes: The simulations revealed molten rock plumes below Africa, potentially caused by tectonic plates subducting into the mantle. These plumes are believed to be a contributing factor to the IOGL.
    • Possible origination: Researchers said that the IOGL comprises slabs from the Tethys Sea, a long-lost sea that plunged into the depths of the planet millions of years ago. Tethys Sea, which once separated the supercontinents of Gondwana and Laurasia is believed to have perturbed the African Large Low Shear Velocity province.

    Future Perspectives

    • Lack of Seismic Evidence: While the simulated models suggest the presence of molten rock plumes beneath the Indian Ocean, seismographic evidence has yet to confirm their actual existence.
    • Additional Factors at Play: The researchers emphasize that other factors contributing to the gravitational anomaly in the Indian Ocean need to be further explored before reaching a definitive conclusion.
    • Further Research: Continuation of studies, including seismic surveys and detailed modelling, is necessary to gain a comprehensive understanding of the IOGL and its causes.

  • Places in news: Ubinas Volcano

    Central Idea

    • Peru declared a state of emergency for sixty days in areas around the Ubinas volcano.
    • The volcano has been spewing ash and gas and is probably set to erupt.

    Ubinas Volcano

    • Ubinas is an active stratovolcano located in the Moquegua Region of southern Peru, approximately 60 kilometers east of the city of Arequipa.
    • It is part of the Central Volcanic Zone of the Andes and stands at an elevation of 5,672 meters above sea level.

    Geological Characteristics

    • Stratovolcano Formation: Ubinas is characterized by its stratovolcano structure, comprising layers of hardened lava, ash, and other volcanic materials.
    • Caldera and Crater: The volcano’s summit contains a 1.4-kilometer-wide and 150-meter-deep caldera, within which lies a smaller crater. This distinct feature adds to the volcano’s geological significance.
    • Ubinas I and Ubinas II: The volcano exhibits an upwards-steepening cone shape, with a notable notch on its southern side. The lower part is referred to as Ubinas I, while the steeper upper section is known as Ubinas II, representing different stages in the volcano’s geological history.

    Volcanic Activity

    • Active Volcanic History: Ubinas is recognized as the most active volcano in Peru, displaying a history of small to moderate explosive eruptions and persistent degassing.
    • Notable Eruptions: The volcano has experienced notable eruptions throughout history, including the 2006–2007 event that resulted in eruption columns, ash fall, health concerns, and evacuations in the region.
    • Recent Activity: From 2013 to 2017, Ubinas exhibited lava flow within the crater, accompanied by ash falls, leading to further evacuations in nearby towns.

    Eruption and Impact

    • Ash and Gas Emissions: The Ubinas volcano has been actively spewing ash and gas.
    • Smoke Cloud and Affected Areas: The smoke cloud generated by the eruption has reached towns located up to 10 kilometers away from the volcano. This has raised concerns for the well-being of approximately 2,000 people residing in the affected areas.
    • The “Ring of Fire”: The region where Ubinas is situated falls within the “Ring of Fire,” an area around the Pacific Ocean known for its high volcanic and seismic activity.

     

  • Indian Ocean Dipole : What is it, how it can limit El Nino effects?

    Central Idea

    • With the El Nino phenomenon set to affect the Indian monsoon this year, there is growing optimism surrounding the development of a positive Indian Ocean Dipole (IOD) and its ability to mitigate the effects of El Nino. The IOD, a weaker ocean-atmosphere interaction in the Indian Ocean, has demonstrated limited impacts in the past but holds potential in offsetting the adverse effects of El Nino, particularly in neighbouring regions.

    *Relevance of the topic*

    *Questions on Indian ocean dipole and El nino and its impact on Indian monsoon have been asked multiple times in previous years.

    *Relate this topic with Indian monsoon, and its impact on Indian agriculture as, Rainfed agriculture occupies about 51 percent of country’s net sown area and accounts for nearly 40 percent of the total food production.

    The current status of the Indian Ocean Dipole (IOD) and El Nino

    • IOD:
    • The IOD is currently in a neutral phase. This means that there is no significant temperature difference between the western and eastern sides of the Indian Ocean along the equator.
    • However, international climate models suggest the possibility of a positive IOD event developing in the coming months.
    • The India Meteorological Department (IMD) has also reported an 80% chance of a positive IOD during the June-August 2023 season. The development of a positive IOD would have implications for weather patterns in the Indian Ocean region.
    • El Nino:
    • El Nino has already established itself in the Pacific Ocean this year. El Nino occurs when the prevailing wind systems weaken, resulting in reduced displacement of warm waters in the eastern side of the Pacific.
    • This abnormal warming of the eastern Pacific can have impacts on global weather patterns, including the Indian monsoon. The presence of El Nino raises concerns about its potential impact on the Indian monsoon rainfall.

    Understanding El Nino and IOD

    Phenomenon El Nino Indian Ocean Dipole (IOD)
    Definition Warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean Ocean-atmosphere interaction in the Indian Ocean
    Cause Weakening or reversal of trade winds Temperature difference between the western and eastern parts of the Indian Ocean along the equator
    Impact on Weather Disrupts atmospheric circulation patterns globally, leading to droughts, floods, and changes in temperature and precipitation patterns Influences regional weather patterns in the Indian Ocean basin and its surrounding landmasses
    Indian Monsoon Suppresses rainfall, leading to drought conditions in some regions Positive IOD enhances rainfall along the African coastline and over the Indian subcontinent; negative IOD suppresses rainfall in affected regions
    Opposite Phase La Nina (cooling of sea surface temperatures in the central and eastern equatorial Pacific) Opposite effects based on the temperature gradient between the western and eastern parts of the Indian Ocean
    Relative Impact Significantly affects global weather patterns Weaker impacts compared to El Nino and La Nina, but still influences local weather patterns

    The interplay between the El Nino Southern Oscillation (ENSO) and IOD

    • Triggering Mechanism: ENSO events, specifically El Nino, can trigger the development of a positive IOD in the Indian Ocean.
    • External Drivers: While external factors such as ENSO can initiate IOD events in some cases, there is evidence to suggest that IOD events can also occur due to local circulations or subsurface processes within the equatorial Indian Ocean.
    • Internal Dynamics: IOD events largely develop and mature through internal dynamics, even when triggered by external drivers. They have the potential to exhibit independent existence and can impact weather patterns in the Indian Ocean region.
    • Impact on IOD: During El Nino, the Pacific side of Indonesia tends to be cooler than normal, which influences the Indian Ocean side, leading to the development of a positive IOD.
    • Mutual Interaction: The circulation patterns of IOD and ENSO can impact each other when both events are strong. The interaction between the two phenomena can influence the intensity and duration of each event.
    • Contrasting Associations: Positive IOD events are often associated with El Nino, while negative IOD events are sometimes linked to La Nina. However, this association is not absolute, and IOD events can occur independently or have different associations depending on the specific conditions.
    • Combined Impacts: Strong IOD and ENSO events can have combined effects on weather patterns, as their circulation patterns can interact and influence each other.

    The impacts of Indian Ocean Dipole

    • Rainfall Distribution: IOD significantly influences rainfall patterns in the Indian Ocean region. During a positive IOD, there is increased convection and rainfall along the African coastline and over the Indian subcontinent. Conversely, a negative IOD leads to suppressed rainfall in these regions.
    • Drought and Floods: Positive IOD events can bring above-average rainfall to the affected regions, which can alleviate drought conditions and replenish water resources. However, this increased rainfall can also result in flooding and water-related disasters in certain areas.
    • Agricultural Productivity: IOD has implications for agriculture as it affects the availability and distribution of rainfall. Positive IOD events can enhance agricultural productivity in the affected regions, while negative IOD events may lead to reduced crop yields and agricultural challenges.
    • Fisheries: IOD impacts the productivity of marine ecosystems. During positive IOD, increased upwelling of nutrient-rich waters occurs, which promotes higher fish stocks and benefits fisheries. In contrast, negative IOD can disrupt the marine food chain and impact fish populations.
    • Coral Bleaching: IOD influences sea surface temperatures, and prolonged positive IOD events can contribute to increased sea surface temperatures in the affected regions. This can lead to coral bleaching, negatively impacting coral reefs and marine biodiversity.
    • Indian Monsoon: IOD can influence the strength and distribution of the Indian monsoon rainfall. Positive IOD events are generally associated with enhanced monsoon rainfall over the Indian subcontinent, while negative IOD events can lead to reduced monsoon rainfall.
    • Weather Extremes: IOD can contribute to the occurrence of extreme weather events such as heatwaves, storms, and tropical cyclones in the Indian Ocean region.
    • Economic and Social Impacts: The impacts of IOD on rainfall, agriculture, fisheries, and other sectors have direct economic and social implications. These impacts can affect livelihoods, water availability, food security, and overall economic development in the affected regions.

    Impacts of El Nino on the Indian monsoon

    • Weakened Monsoon Winds: During El Nino, the trade winds that blow from the east across the Indian Ocean weaken. These winds are responsible for carrying moisture-laden air towards the Indian subcontinent, facilitating the monsoon rainfall. With weakened winds, the supply of moisture is reduced, leading to a decrease in rainfall.
    • Delayed Onset: El Nino can cause a delayed onset of the Indian monsoon. The normal onset of monsoon rainfall in India is around June, but during El Nino years, the monsoon arrival may be delayed, resulting in a late start to the rainy season.
    • Deficient Rainfall: El Nino events often lead to below-average rainfall during the monsoon season in India. The reduced moisture transport and altered atmospheric circulation associated with El Nino result in deficient rainfall across various parts of the country.
    • Regional Variations: The impact of El Nino on the Indian monsoon is not uniform throughout the country. Certain regions, particularly central and northern India, are more prone to experiencing below-average rainfall during El Nino years. However, some areas in southern India may receive near-normal or even above-normal rainfall during these periods.
    • Drought Conditions: El Nino-induced deficient rainfall can result in drought conditions in affected regions. This can have adverse effects on agriculture, water availability, and livelihoods, leading to crop failures, reduced agricultural productivity, and water scarcity.
    • Temperature Extremes: El Nino can contribute to increased temperatures during the monsoon season in some parts of India. The reduced cloud cover and rainfall can lead to heatwaves and higher temperatures, posing health risks and impacting human well-being.

    Conclusion

    • While the IOD’s ability to counterbalance the effects of El Nino is limited, there is hope that a positive IOD event may develop in the coming months. Past instances, such as the strong IOD event in 2019, have demonstrated the potential of IOD in compensating for monsoon rainfall deficits. As researchers continue to study the interplay between ENSO and IOD, the development of a positive IOD this year would be welcomed, offering some respite from the anticipated impacts of El Nino on the Indian monsoon.

    Also read:

    What is El Nino and How it impacts the Monsoon?

     

  • 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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  • Zero Shadow Day: What is it, why does it happen?

    shadow

    Central idea: Many cities across India are experiencing Zero Shadow Day since the sun was directly overhead at that time.

    What is Zero Shadow Day?

    • Zero Shadow Day is a phenomenon that occurs twice a year at every point on Earth located between the Tropic of Cancer and the Tropic of Capricorn.
    • During Zero Shadow Day, vertical objects appear to cast no shadow at local noon, when the sun is at its zenith directly above the object.
    • It occurs when the sun’s location moves from 23.5°N to 23.5°S of Earth’s equator and back, causing the shadow to disappear beneath objects at local noon.

    Why does it happen?

    • It occurs due to the movement of the sun from south to north during the Uttarayan and back from north to south during Dakshinayan.
    • This movement is caused by Earth’s rotation axis being tilted at an angle of roughly 23.5° to the axis of revolution around the sun.
    • All places whose latitude equals the angle between the sun’s location and the equator on that day experience Zero Shadow Day, with the shadow disappearing at local noon.

    Try this PYQ:

    On 21st June, the Sun-

    (a) Does not set below the horizon at the Arctic Circle

    (b) Does not set below the horizon at Antarctic Circle

    (c) Shines vertically overhead at noon on the Equator

    (d) Shines vertically overhead at the Tropic of Capricorn

     

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