Previse 2024: Geography: Terms in News

Previse 2024: Geography: Terms in News

GS1 | Geography

Table of contents

Understanding geographical concepts, from climate change and natural disasters to geopolitical conflicts and resource exploration, is essential for interpreting the news with a deeper lens.

This section unpacks key geography terms making headlines, empowering you to grasp the spatial context of current events.

Pacific Decadal Oscillation 

  • A phenomenon that makes cyclones more frequent by combining global warming and the Pacific Decadal Oscillation (PDO).
  • Basically, it is a long-term ocean fluctuation in the Pacific Ocean.
  • Negative PDO, when encountered in the La Nina phase, creates suitable conditions for tropical cyclones. 
  • PDO entered a cooler or negative phase in 2019.
  • The oscillation has two phases- 
    • Cool or Negative Phase in which the Eastern Equatorial Pacific has lower than normal sea surface temperatures.
    • Warm or Positive phase in which the Western Pacific Ocean has higher than normal sea surface temperatures.

Blue Hole

  • Blue Hole is a massive underwater sinkhole recently discovered off the coast of the Yucatan Peninsula in Mexico.
  • It is believed to have formed during the Ice Age when the sea level was 100–120 m lower than it is today.
  • It is a microbial biodiversity hotspot and gets its name due to indigo centres and light blue perimeters.
  • It is the deepest blue hole on Earth.

WISE Report 

  • The Water, Ice, Society, and Ecosystems (WISE) report for the Hindu Kush Himalaya was released by the International Centre for Integrated Mountain Development (ICIMOD).
  • It reveals that glaciers disappeared 65% faster in the 2010s than in the last decade.
  • The accelerated glacier melt means that the ‘peak water’ stage (the supply of fresh snow water due to glacier melt is the highest ever) will reach around mid-century and decrease.
  • ICIMOD is an intergovernmental organization that focuses on climate and environmental risks, green economies, and sustainable action.
  • The members include Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal, and Pakistan.

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  • When Arctic Ocean water becomes saltier and warmer, it is known as Atlantification.
  • This occurs when warm water from the Atlantic Ocean is advected into the Arctic Ocean in increasing amounts.
  • The Barents Sea is a marginal water body in the Arctic Ocean that is starting to resemble the Atlantic Ocean.
  • The top of the Arctic Ocean is covered by sea ice, but below this layer, freshwater and a deeper layer of warmer, saltier water are delivered to the Arctic from the Atlantic Ocean.
  • The main driving force behind this occurrence is the process called Arctic Dipole.

Shelf Cloud 

  • Shelf clouds, also known as Arcus clouds, were recently seen in Uttarakhand.
  • They are associated with powerful storm systems, commonly known as wall clouds, rotation clouds or funnel clouds.
  • The mechanism for their formation includes a cold downdraft from a cumulonimbus cloud reaching the ground and the rapid spreading of cold air along the ground, which pushes the warm, moist air upwards.
  • There are times when they are seen below the cumulonimbus clouds as dense and towering vertical clouds, causing intense rain.
  • Rising air condenses the water vapour into the patterns associated with shelf clouds.

Indian Ocean Geoid Low

  • A geoid is a ‘gravity hole’ having anomalies on Earth's map, and the Indian Ocean Geoid Low (IOGL) is an approximately three million square kilometres-wide gravity hole in the Indian Ocean.
  • It is located just south of Sri Lanka because the Earth’s gravitational pull is weakest there. It is also the lowest geoid on Earth.
  • The sea level is also 100 meters lower than the global average sea level.
  • This is caused due to rising plumes of molten rock along the edges of Tethys Ocean bed.

Khazan Land

  • Khazan Land is a stretch of low-lying, saline, water-logged coastal wetlands of Goa influenced by tidal flows.
  • The estuarine agricultural system called Khazan farming is a carefully topo-hydro-engineered agro-aquaculture ecosystem based on the regulation of salinity and tides.
  • It has an important role in the ecosystem, serving as the main drainage system for floodwater.
  • It is reclaimed from mangrove forests through an intricate system of sluice gates, dykes and canals.
  • The Salim Ali Bird Sanctuary in the low-lying floodplains of Goa is an important example.


  • It was documented at Mount Saraswati in the Hanle Valley of Changthang, Ladakh, by the Indian Astronomical Observatory.
  • They are usually visible near poles at any time of day but can be seen only at night with the naked eye.
  • Auroras are patterns of bright lights in the sky caused by the interaction of particles ejected by the Sun during coronal mass ejection with the magnetic field around the Earth.
  • The shape of Earth's magnetic field contributes to the creation of auroras, which are of two types-
    • Northern lights (Aurora borealis) in the Northern Hemisphere
    • Southern lights (Aurora australis) in the Southern Hemisphere

Omega Blocking

  • After the recent floods in the Mediterranean region, a low-pressure system shaped like an Omega Block formed over the Netherlands.
  • They are also linked to heatwaves when a high-pressure pattern blocks and diverts the jet stream due to which a mass of hot air flows up from northern Africa and the Iberian peninsula.
  • When two low-pressure systems are cut off from the main flow of the jet stream and a high-pressure system is sandwiched between them, the structure resembles Ω.
  • This event is linked to other extreme events such as heatwaves in France & Germany, Pakistan floods, etc.
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