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Subject: Geographical Features

  • Monsoon onset over Kerala delayed: IMD

    • The monsoon’s arrival over Kerala has been delayed to June 3, according to an update by the India Meteorological Department (IMD).
    • Private weather forecast agency, Skymet, however, said that the monsoon had arrived.
    • This was because two of the three criteria — as defined by the IMD — had been met.
    • Currently, IMD’s own data indicated that except for the OLR, the other criteria were met. Thus, there is an element of subjectivity in arrival.

    What are those criterias defined by IMD?

    1. Rain-bearing westerlies being at a minimum depth and speed;
    2. At least 60% of the available 14 stations in Kerala and coastal Karnataka, reporting rainfall of 2.5 mm or more for two consecutive days after May 10;
    3. A certain degree of clouding, indicated by a parameter called ‘outgoing long wave radiation’ (OLR), being below 200 W/square meter.

    What is meant by ‘Outgoing Long Wave Radiation’ (OLR)?

    • Outgoing Long-wave Radiation (OLR) is electromagnetic radiation of wavelengths from 3–100 μm emitted from Earth and its atmosphere out to space in the form of thermal radiation.
    • It is also referred to as up-welling long-wave radiation and terrestrial long-wave flux, among others.
    • The flux of energy transported by outgoing long-wave radiation is measured in W/m.
    • In the Earth’s climate system, long-wave radiation involves processes of absorption, scattering, and emissions from atmospheric gases, aerosols, clouds and the surface.
    • Over 99% of outgoing long-wave radiation has wavelengths between 4 μm and 100 μm, in the thermal infrared part of the electromagnetic spectrum.

    Factors responsible for south-west monsoon formation:

    1. Intense heating of Tibetan plateau during summer months.
    2. Permanent high pressure cell in the South Indian Ocean (east to north-east of Madagascar in summer).

    Factors that influence the onset of south-west monsoons:

    1. Above points +
    2. Subtropical Jet Stream (STJ).
    3. Tropical Easterly Jet (African Easterly Jet).
    4. Inter Tropical Convergence Zone.

    Factors that influence the intensity of south-west monsoons:

    1. Strengths of Low pressure over Tibet and high pressure over southern Indian Ocean.
    2. Somali Jet (Findlater Jet).
    3. Somali Current (Findlater Current).
    4. Indian Ocean branch of Walker Cell.
    5. Indian Ocean Dipole.

    Factors responsible for north-east monsoon formation:

    1. Formation and strengthening of high pressure cells over Tibetan plateau and Siberian Plateau in winter.
    2. Westward migration and subsequent weakening of high pressure cell in the Southern Indian Ocean.
    3. Migration of ITCZ to the south of India.

  • What is a Supermoon?

    The Moon will have the nearest approach to Earth on May 26, and therefore will appear to be the closest and largest Full Moon or “supermoon” of 2021.

    Tap here to read more about Solar and Lunar Eclipses

    What is a Supermoon?

    • A supermoon occurs when the Moon’s orbit is closest to the Earth at the same time that the Moon is full.
    • As the Moon orbits the Earth, there is a point of time when the distance between the two is the least (called the perigee when the average distance is about 360,000 km from the Earth).
    • Also, there is a point of time when the distance is the most (called the apogee when the distance is about 405,000 km from the Earth).
    • Now, when a full moon appears at the point when the distance between the Earth and the Moon is the least, not only does it appear to be brighter but it is also larger than a regular full moon.
    • According to NASA, the term supermoon was coined by astrologer Richard Nolle in 1979.
    • In a typical year, there may be two to four full supermoons and two to four new supermoons in a row.

    What is happening today?

    • Two celestial events will take place at the same time.
    • One is the supermoon and the other is a total lunar eclipse, which is when the Moon and Sun are on opposite sides of the Earth.
    • Because of the total lunar eclipse, the moon will also appear to be red.
    • This is because the Earth will block some of the light from the Sun from reaching the moon.
    • The Earth’s atmosphere filters the light, it will soften “the edge of our planet’s shadow” “giving the Moon a deep, rosy glow.”

  • Eruption of Mount Nyiragongo

    Thousands have fled a volcanic eruption in the Democratic Republic of Congo from Mount Nyiragongo on the outskirts of Goma City.

    These were some volcanoes in news this year:

    Mount Vesuvius, Taal Volcano, La Soufriere

    Mount Nyiragongo

    • Mount Nyiragongo is an active stratovolcano with an elevation of 3,470 m (11,385 ft) in the Virunga Mountains associated with the Albertine Rift.
    • The main crater is about 2km wide and usually contains a lava lake.
    • The crater presently has two distinct cooled lava benches within the crater walls.
    • It is one of the 16 Decade Volcanoes.
    • Nyiragongo’s lava lake has at times been the most voluminous known lava lake in recent history. The depth of the lava lake varies considerably.
    • Nyiragongo and nearby Nyamuragira are together responsible for 40 percent of Africa’s historical volcanic eruptions.

    Answer this PYQ in the comment box:

    Q.Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth?

    1. Volcanic action
    2. Respiration
    3. Photosynthesis
    4. Decay of organic matter

    Select the correct answer using the code given below:

    (a) 1 and 3 only

    (b) 2 only

    (c) 1, 2 and 4 only

    (d) 1, 2, 3 and 4

    What are Decade Volcanoes?

    • The Decade Volcanoes are 16 volcanoes identified by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI).
    • They are considered worthy of particular study in light of their history of large, destructive eruptions and proximity to densely populated areas.
    • They are named Decade Volcanoes because the project was initiated in the 1990s as part of the United Nations-sponsored International Decade for Natural Disaster Reduction.

  • Cyclone Tauktae

    Cyclone Tauktae (pronounced Tau-Te), classified as a very severe cyclonic storm (VSCS) and developed in the Arabian Sea, is wreaking havoc all across the Indian Coast.

    Don’t you think?

     In recent years, strong cyclones have been developing in the Arabian Sea more frequently than earlier.

    Cyclone Tauktae

    • Tauktae is a currently active and strengthening tropical cyclone threatening the state of Gujarat in India and impacting the states Karnataka, Goa and Maharashtra.
    • It is the fourth cyclone in consecutive years to have developed in the Arabian Sea, that too in the pre-monsoon period (April to June).
    • All these cyclones since 2018 have been categorised as either ‘Severe Cyclone’ or above.
    • Once Tauktae makes its landfall, three of these will have hit either the Gujarat or Maharashtra coast.
    • After Cyclone Mekanu in 2018, which struck Oman, Cyclone Vayu in 2019 struck Gujarat, followed by Cyclone Nisarga in 2020 that struck Maharashtra.

    What is aiding such rapid intensification?

    • Any tropical cyclone requires energy to stay alive.
    • This energy is typically obtained from the warm water and humid air over the tropical ocean.
    • Currently, seawater up to depths of 50 metres has been very warm, supplying ample energy to enable the intensification of Cyclone Tauktae.
    • The more the heat released through condensation of water vapour, the steeper the drop in pressure.
    • A low-pressure system undergoes multiple stages of intensification to form cyclones.

    Not a rare phenomenon

    • Typically, tropical cyclones in the North Indian Ocean region (the Bay of Bengal and the Arabian Sea) develop during the pre-monsoon and post-monsoon (October to December) periods.
    • May-June and October-November are known to produce cyclones of severe intensity that affect the Indian coasts.

    Is the Arabian Sea becoming cyclone-friendly?

    • Annually, five cyclones on average form in the Bay of Bengal and the Arabian Sea combined.
    • Of these, four developments in the Bay of Bengal, which is warmer than the Arabian Sea.
    • In the Arabian Sea, cyclones typically develop over the Lakshadweep area and largely traverse westwards, or away from India’s west coast.
    • However, in recent years, meteorologists have observed that the Arabian Sea, too, has been warming. This is a phenomenon associated with global warming.

    Back2Basics: Tropical Cyclone

    • A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure centre, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rains.
    • Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone.
    • A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and the northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean.
    • In the south Pacific or the Indian Ocean, comparable storms are referred to simply as “tropical cyclones” or “severe cyclonic storms”.

    Also read:

    [Burning Issue] Tropical Cyclones and India

  • Major seismic hazard along Assam faultline

    Location of epicentre

    • An earthquake of magnitude 6.4 on the Richter scale hit Assam around 8 am on Wednesday.
    • The primary earthquake had its epicentre at latitude 26.690 N and longitude 92.360 E, about 80 km northeast of Guwahati, and a focal depth of 17 km, the National Centre for Seismology (NCS) said.

    The faultline

    • The preliminary analysis shows that the events are located near to Kopili Fault closer to Himalayan Frontal Thrust (HFT).
    • The Kopili Fault is a 300-km northwest-southeast trending fault from the Bhutan Himalaya to the Burmese arc.
    • The fault is a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture.
    • The area is seismically very active falling in the highest Seismic Hazard zone V associated with collisional tectonics where Indian plate sub-ducts beneath the Eurasian Plate the NCS report said.
    • HFT, also known as the Main Frontal Thrust (MFT), is a geological fault along the boundary of the Indian and Eurasian tectonic plates.

    Need for earthquake preparedness

    • The Northeast is located in the highest seismological zone, so we must have constant earthquake preparedness at all levels.
    • Continuous tectonic stress keeps building up particularly along the faultlines.
    • Today’s earthquake was an instance of accumulated stress release — probably, stress was constrained for a fairly long time at this epicentre, and hence the release was of relatively higher intensity.

  • La Soufriere volcanic eruption

    Sulphur dioxide (SO2) emissions from La Soufriere volcano eruption in the Caribbean have reached all the way to India.

    Why in news?

    • Its eruption has sparked fear of increased pollution levels in the northern parts of India and acid rain.
    • Volcanic plumes can cause aviation and air quality hazards.

    La Soufriere

    • It is an active stratovolcano on the Caribbean island of Saint Vincent in Saint Vincent and the Grenadines.
    • It is the highest peak in Saint Vincent and has had five recorded explosive eruptions since 1718.

    Impact of such eruptions

    • Volcanic emissions reaching the stratosphere can have a cooling effect on global temperatures.
    • The most significant climate impacts from volcanic injections into the stratosphere come from the conversion of sulphur dioxide to sulphuric acid, which condenses rapidly in the stratosphere to form fine sulphate aerosols.
    • The aerosols increase the reflection of radiation from the Sun back into space, cooling the Earth’s lower atmosphere or troposphere.

    Try this PYQ:

    Q.Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth?

    1. Volcanic action
    2. Respiration
    3. Photosynthesis
    4. Decay of organic matter

    Select the correct answer using the code given below:

    (a) 1 and 3 only

    (b) 2 only

    (c) 1, 2 and 4 only

    (d) 1, 2, 3 and 4

  • How Asian desert dust enhances Indian summer monsoon?

    A new study has revealed how dust coming from the deserts in West, Central and East Asia plays an important role in the Indian Summer Monsoon.

    Try this PYQ:

    With reference to ‘Indian Ocean Dipole (IOD)’, sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct?

    1. IOD phenomenon is characterized by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
    2. An IOD phenomenon can influence an El Nino’s impact on the monsoon.

    Select the correct Option using the code given below:

    (a) Only 1

    (b) Only 2

    (c) Both 1 and 2

    (d) Neither 1 nor 2

    Why study dust?

    • Many studies have shown that the dust emission scheme is extremely sensitive to climate change.
    • Understanding these mechanisms and effects of dust will help us understand our monsoon systems in the face of global climate change.

    Impact of dust on Indian Monsoon

    • Dust swarms from the desert when lifted by strong winds can absorb solar radiation and become hot.
    • This can cause heating of the atmosphere, change the air pressure, wind circulation patterns, influence moisture transport and increase precipitation and rainfall.
    • A strong monsoon can also transport air to West Asia and again pick up a lot of dust.
    • The researchers say this is a positive feedback loop.

    Role of the Iranian plateau

    • Not just the dust from the Middle East, the Iranian Plateau also influences the Indian Summer Monsoon.
    • The hot air over the Iranian Plateau can heat the atmosphere over the plateau, strengthen the circulation over the deserts of the Arabian Peninsula and increase dust emission from the Middle East.
    • The researchers also explain how the Indian Summer Monsoon has a reverse effect and can increase the winds in West Asia to produce yet more dust.

    Transported aerosols

    • Deserts across the globe play important roles in monsoons.
    • The dust aerosols from deserts in West China such as the Taklamakan desert and the Gobi Desert can be transported eastward to eastern China and can influence the East Asia summer monsoon.
    • And in the southwest United States, we have some small deserts that influence the North African monsoon.

    Anthropogenic contributions

    • Some studies have found that the anthropogenic aerosols emitted from the Indian subcontinent can decrease summer monsoon precipitation.
    • However, some others found that absorbing aerosols such as dust can strengthen the monsoon circulation.

    Minor components

    • Earlier it was believed that dust from deserts across the globe will have the same components.
    • But it was found that different deserts have different chemical compositions and this can influence the dust’s properties.
    • For example, dust from the Middle East has the more absorbing ability of solar radiation than dust from North Africa and this difference in absorbing ability might influence monsoon systems.

  • Indian monsoon 25 million years ago resembled present day Australia’s

    Using leaf fossils, researchers have found that the Indian monsoon 25 million years ago resembled present-day Australia’s.

    Try this PYQ:

    Q.Which one of the following is the appropriate reason for considering the Gondwana rocks as the most important rock systems of India?

    (a) More than 90% of limestone reserves of India are found in them

    (b) More than 90% of India’s coal reserves are found in them

    (c) More than 90% of fertile black cotton soils are spread over them

    (d) None of the reasons given above is appropriate in this context

    India’s drift

    • About 180 million years ago, India separated from the ancient supercontinent Gondwana and took a long northward journey of about 9,000 km to join Eurasia.
    • During this journey, the subcontinent moved from the southern hemisphere, crossed the Equator to reach its current position in the northern hemisphere.
    • Due to these changing latitudes, it experienced different climatic conditions, and a new study has now tried to map these climatic variations using leaf fossils.

    Clueless over the evolution of monsoon

    • The evolution of the monsoonal climate in India is still debatable and not fully understood.
    • Though recent data indicates that the monsoon system we experience now dates back to about 25 million years, it is still unclear how the climate was during its long voyage.

    Indian research

    • The researchers analysed the morphological characters of fossil leaves collected from Deccan Volcanic Province, East Garo Hills of Meghalaya, Gurha mine in Rajasthan and Makum Coalfield in Assam.
    • The four fossil assemblages were found to be from four different geological ages.
    • It has been observed from across the globe that plant leaf morphological characters such as apex, base and shape are ecologically tuned with the prevailing climatic conditions.
    • The research applied this model to characterize the past monsoon from fossil leaves.

    It’s finding

    • The results indicated that the fossil leaves from India were adapted to an Australian type of monsoon and not the current Indian monsoon system during its voyage.
    • The reconstructed temperature data show that the climate was warm (tropical to subtropical) at all the studied fossil sites with temperatures varying from 16.3–21.3 degrees C.
    • All the fossil sites experienced high rainfall, which varied from 191.6 cm to 232 cm.

  • What is Rule Curve of a river?

    The Supreme Court has warned the Tamil Nadu Chief Secretary against the failure to give information on the rule curve for Mullaperiyar dam.

    Do you know?

    The Mullaperiyar dam is located in Kerala on the river Periyar but is operated and maintained by the neighbouring state of Tamil Nadu.

    What is the Rule Curve?

    • A rule curve or rule level specifies the storage or empty space to be maintained in a reservoir during different times of the year.
    • Here the implicit assumption is that a reservoir can best satisfy its purposes if the storage levels specified by the rule curve are maintained in the reservoir at different times.
    • It decides the fluctuating storage levels in a reservoir.
    • The gate opening schedule of a dam is based on the rule curve.
    • It is part of the “core safety” mechanism in a dam.

    Why such a move?

    • During the high-voltage hearing, the Tamil Nadu government blamed Kerala for delaying the finalization of the rule curve for the 123-year-old dam.
    • Kerala government has accused Tamil Nadu of adopting an “obsolete” gate operation schedule dating back to 1939.

    About Mullaperiyar Dam

    • Mullaperiyar Dam is a masonry gravity dam on the Periyar River in the Indian state of Kerala.
    • It is located on the Cardamom Hills of the Western Ghats in Thekkady, Idukki District of Kerala.
    • It was constructed between 1887 and 1895 by John Pennycuick and also reached an agreement to divert water eastwards to the Madras Presidency area (present-day Tamil Nadu).
    • It has a height of 53.6 m from the foundation, and a length of 365.7 m.
    • The Periyar National Park in Thekkady is located around the dam’s reservoir.
    • The dam is built at the confluence of Mullayar and Periyar rivers.

  • Places in news: Mount Sinabung

    Indonesia’s Mount Sinabung volcano sent a cloud of hot ash as high as 3 km today, in its first big eruption since August last year.

    Mount Sinabung

    • It is a Pleistocene-to-Holocene stratovolcano in the Karo plateau of Karo Regency, North Sumatra, Indonesia.
    • It is created by the subduction of the Indo-Australian Plate under the Eurasian Plate.
    • It erupted in 2010 after a 400-year-long hiatus and has been continuously active since September 2013.

    Why frequent eruptions?

    • Indonesia straddles the “Pacific ring of fire” with nearly130 active volcanoes, more than any other country.
    • Sinabung had been inactive for centuries before it erupted again in 2010.

    Try this PYQ:

    Q.Consider the following statements:

    1. The Barren Island volcano is an active volcano located in the Indian Territory.
    2. Barren Island lies about 140 km east of Great Nicobar
    3. The last time the Barren Island volcano erupted was in 1991 and it has remained inactive since then.

    Which of the statements given above is/are correct? (CSP 2018)

    (a) 1 only

    (b) 2 and 3 only

    (c) 3 only

    (d) 1 and 3

    What is the Pacific ring of fire?

    • The Pacific Ring of Fire is a region around much of the rim of the Pacific Ocean where many volcanic eruptions and earthquakes occur.
    • It includes the Pacific coasts of South America, North America and Kamchatka, and some islands in the western Pacific Ocean.
    • It is a direct result of plate tectonics: specifically the movement, collision and destruction of lithospheric plates under and around the Pacific Ocean.
    • The collisions have created a nearly continuous series of subduction zones, where volcanoes are created and earthquakes occur.