GS Notes

1.5 - Geography Notes 34

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Elaborate Notes

Heat Dome

A heat dome is a large-scale meteorological phenomenon where a persistent area of high pressure traps hot air over a region, acting like a lid or cap on the atmosphere. This prevents the hot air from escaping and leads to a significant build-up of heat near the surface, causing prolonged periods of anomalously high temperatures.

  • Mechanism of Formation: The formation is a complex interplay of atmospheric dynamics.
    • Role of High-Pressure Systems: It begins with a strong ridge of high pressure in the upper atmosphere. Air under high pressure sinks towards the surface (subsidence). As this air sinks, it is compressed and warms up adiabatically. This sinking air also acts as a cap, preventing convection and cloud formation, which allows for maximum solar radiation to reach the ground, further intensifying the surface heating.
    • Role of Jet Streams: The jet stream, a fast-flowing river of air in the upper atmosphere, plays a crucial role. A stable and strong jet stream typically flows in a relatively straight, zonal (west-to-east) pattern. However, when the jet stream weakens, it becomes more wavy and begins to meander significantly in a north-south direction. These large meanders are known as Rossby waves. A heat dome often forms when a Rossby wave becomes highly amplified and stationary, creating what is known as an Omega block (named for its resemblance to the Greek letter Ω). The warm air gets trapped inside the high-pressure ridge of this block.
    • Influence of Ocean Temperatures (La Niña): The summary mentions the role of La Niña. During a La Niña event, the sea surface temperatures in the central and eastern equatorial Pacific are cooler than average. This alters global atmospheric circulation patterns. The 2021 Pacific Northwest heat wave, affecting Canada and the USA, was linked by some scientists, including those at the National Oceanic and Atmospheric Administration (NOAA), to the downstream effects of La Niña. The temperature gradient created by La Niña can contribute to the amplification and stalling of Rossby waves over North America. The warm air from the tropical Pacific is pushed northwards, while the high-pressure system descends, trapping this heat.
  • The 2021 North American Event: In June 2021, a severe heat dome settled over western Canada and the Pacific Northwest of the United States. Lytton, British Columbia, recorded a temperature of 49.6°C, setting an all-time high-temperature record for Canada. This extreme event was analyzed by the World Weather Attribution initiative, which concluded in a 2021 rapid attribution study that the event was “virtually impossible without human-caused climate change.”

Tides

Tides are the periodic, short-term rise and fall of sea level, primarily caused by the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth. This phenomenon was first explained scientifically by Isaac Newton in his Principia Mathematica (1687) through his Law of Universal Gravitation.

  • Gravitational and Centrifugal Forces:
    • Gravitational Pull: The Moon, being much closer to the Earth than the Sun, exerts a stronger gravitational pull on Earth’s waters. This pull creates a “bulge” of water on the side of the Earth facing the Moon. The Sun’s gravitational effect is about 46% that of the Moon’s.
    • Centrifugal Force: As the Earth-Moon system revolves around its common center of mass (the barycenter), a centrifugal force is generated. This force is equal and opposite across the Earth. On the side of the Earth opposite the Moon, this centrifugal force is greater than the Moon’s gravitational pull, causing a second water bulge to form.
    • Resulting Tides: The two bulges represent high tides. The areas between the bulges, from which water is drawn, experience low tides. As the Earth rotates on its axis, a specific location passes through these two bulges and two troughs each day, typically resulting in two high tides and two low tides approximately every 24 hours and 50 minutes (a lunar day).
  • Factors Affecting Tides:
    • Relative Position of Sun and Moon: The alignment of the Sun, Earth, and Moon dictates the amplitude of the tides.
    • Uneven Water Distribution and Topography: The idealized model of two bulges is modified by the actual geography of the Earth. Continents obstruct the free movement of the tidal bulges, and the shape, size, and depth (bathymetry) of ocean basins and coastlines cause significant variations in tidal range and timing.
  • Types of Tides:
    • Based on Frequency:
      • Semi-diurnal Tides: Characterized by two high tides and two low tides each day, with the successive high and low tides being of approximately equal height. This is the most common tidal pattern, found along coastlines like the eastern seaboard of the USA.
      • Diurnal Tides: Experience only one high tide and one low tide each day. This occurs in locations such as the Gulf of Mexico and parts of Southeast Asia.
      • Mixed Tides: Have two high tides and two low tides per day, but with significant inequality in their heights. The Pacific coast of the USA experiences this pattern.
    • Based on Sun-Moon-Earth Alignment:
      • Spring Tides: Occur when the Sun, Moon, and Earth are aligned in a straight line, a position known as Syzygy. This happens during the full moon (Opposition: M-E-S) and the new moon (Conjunction: E-M-S). The gravitational forces of the Sun and Moon combine, producing the highest high tides and the lowest low tides, resulting in the maximum tidal range.
      • Neap Tides: Occur when the Sun and Moon are at right angles to each other relative to the Earth, a position known as Quadrature. This happens during the first and third quarter moon phases. The gravitational pull of the Sun partially cancels out the pull of the Moon, leading to the lowest high tides and the highest low tides, resulting in the minimum tidal range.
  • Significance of Tides: Tides play a critical role in coastal geomorphology, ecosystems, and human activities. They help create unique ecosystems like mangrove forests and salt marshes. Historically, they have been crucial for maritime trade and navigation, especially for tidal ports like London and Kandla (Deendayal Port). For instance, the Diamond Harbour in West Bengal relies heavily on tidal variations for navigation.

Maritime Zones

The legal framework governing maritime zones is codified in the United Nations Convention on the Law of the Sea (UNCLOS), 1982. This treaty, often called the “Constitution for the oceans,” establishes a comprehensive regime of law and order in the world’s oceans and seas.

  • Baseline: This is the line from which the limits of a state’s maritime zones are measured. Normally, it is the low-water line along the coast as marked on large-scale charts officially recognized by the coastal state. In cases of deeply indented coastlines or a fringe of islands, a system of straight baselines joining appropriate points may be used.
  • Internal Waters: These are waters on the landward side of the baseline, including bays, rivers, and lakes. The coastal state has full sovereignty over its internal waters, equivalent to its land territory. There is no right of innocent passage for foreign vessels in internal waters, unlike in the territorial sea.
  • Territorial Sea: This zone extends up to 12 nautical miles (nm) from the baseline. The coastal state exercises full sovereignty over the sea, its seabed and subsoil, and the airspace above it. However, this sovereignty is subject to the right of innocent passage for foreign ships, which means passage that is not prejudicial to the peace, good order, or security of the coastal state. Submarines are required to navigate on the surface and show their flag.
  • Contiguous Zone: This zone extends from the outer edge of the territorial sea up to 24 nm from the baseline. In this zone, a coastal state can exercise control necessary to prevent or punish infringement of its customs, fiscal, immigration, or sanitary laws and regulations within its territory or territorial sea. Sovereignty does not extend to the airspace above this zone.
  • Exclusive Economic Zone (EEZ): The EEZ extends up to 200 nm from the baseline. In this zone, the coastal state has sovereign rights for the purpose of exploring, exploiting, conserving, and managing the natural resources, whether living (e.g., fisheries) or non-living (e.g., oil and gas, minerals), of the waters superjacent to the seabed and of the seabed and its subsoil. It also has jurisdiction over artificial islands, marine scientific research, and the protection of the marine environment.
    • Extended Continental Shelf: If a state’s continental shelf naturally extends beyond 200 nm, it can claim rights over the seabed and subsoil resources (but not the water column above) up to 350 nm from the baseline or 100 nm from the 2,500-meter isobath, subject to submission and validation by the Commission on the Limits of the Continental Shelf (CLCS).
  • High Seas: These are all parts of the sea that are not included in the EEZ, territorial sea, or internal waters of a state. The high seas are open to all states, and no state may validly purport to subject any part of them to its sovereignty. Freedoms include navigation, overflight, laying submarine cables, fishing, and scientific research. The seabed and ocean floor beyond the limits of national jurisdiction are known as “the Area,” and its resources are designated as the “common heritage of mankind,” managed by the International Seabed Authority (ISA).

Biogeography and Soil

Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Soil science, or pedology, is a key component, as soil is the fundamental medium linking geology, climate, and biology.

  • Soil Defined: Soil is the upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles. The Russian scientist Vasily Dokuchaev (1846-1903) is credited as the father of modern soil science. He was the first to recognize soil as a complex, independent natural body formed by the interplay of various factors, not just disintegrated rock.
  • Soil Profile and Horizons: A soil profile is a vertical cross-section of the soil, from the surface down to the parent material. It reveals distinct layers called horizons.
    • O Horizon: The uppermost layer, composed of organic matter (humus), such as decomposing leaves and twigs.
    • A Horizon: Topsoil, a dark layer rich in humus and minerals. It is the zone of maximum biological activity.
    • E Horizon: The zone of eluviation (leaching). It is a light-colored layer from which minerals like iron and aluminum oxides, and clay have been washed out.
    • B Horizon: Subsoil, the zone of illuviation (accumulation). It is where the materials leached from the E horizon accumulate. It is often rich in clay and minerals.
    • C Horizon: The layer of regolith—large, weathered rock fragments derived from the parent material below. It represents the transition between soil and bedrock.
    • R Horizon: The unweathered parent rock or bedrock.

Soil Formation

The process of soil formation, or pedogenesis, is governed by a set of interacting factors, famously summarized by the pedologist Hans Jenny in his 1941 work Factors of Soil Formation with the equation: S = f(cl, o, r, p, t, …), where S is soil and the factors are climate, organisms, relief, parent material, and time.

  • Factors of Soil Formation (CLORPT):
    • Parent Material (p): This is the geological material from which the soil develops. It determines the soil’s initial mineralogical composition and texture. For example, soils derived from granite are often sandy and acidic, while soils from basalt are typically clay-rich and fertile.
    • Climate (cl): This is often the most influential factor. Temperature and precipitation govern the rate of chemical weathering and the decomposition of organic matter. Humid climates promote intense leaching, leading to acidic soils (pedalfers), while arid climates lead to the accumulation of salts and calcium carbonate (pedocals).
    • Organisms (o): Flora, fauna, and microorganisms contribute to soil formation. Plants supply organic matter, microorganisms decompose it to form humus, and burrowing animals like earthworms aerate and mix the soil. The work of Charles Darwin in The Formation of Vegetable Mould through the Action of Worms (1881) highlighted the profound impact of bioturbation.
    • Relief (r): Topography influences soil formation primarily through its effect on drainage and erosion. Steep slopes have thin, poorly developed soils due to high rates of erosion and runoff. Flat areas in lowlands may have thick, deep soils but can be poorly drained.
    • Time (t): Soil formation is a slow process. A mature soil profile with well-developed horizons takes hundreds to thousands of years to form. Over time, the influence of parent material decreases while the influence of climate becomes more dominant.
  • Soil Formation Processes:
    • Transformational Processes: These involve the chemical and physical alteration of materials within the soil. Examples include the weathering of primary minerals (like feldspar) into secondary minerals (like clay) and the decomposition of organic matter into humus (humification).
    • Translocational Processes: These involve the movement of materials up or down the soil profile.
      • Eluviation: The process by which materials (like clay, iron, organic compounds) are washed out from an upper soil horizon (typically the A or E horizon) by percolating water.
      • Illuviation: The subsequent accumulation or deposition of the eluviated materials in a lower horizon (typically the B horizon).
      • Leaching: A specific type of eluviation where soluble minerals are completely removed from the soil profile by water. This is common in regions with high rainfall and leads to nutrient-poor, acidic soils.

Prelims Pointers

  • Heat Dome Conditions: A combination of a strong, stationary high-pressure system, a weakened and meandering jet stream (Rossby waves), and often influenced by oceanic conditions like La Niña.
  • 2021 Heat Wave: Occurred in the Pacific Northwest of the USA and Western Canada. Lytton, British Columbia, set an all-time temperature record for Canada.
  • Tides: The periodic rise and fall of sea level.
  • Primary Cause of Tides: Gravitational pull of the Moon and the Sun.
  • Secondary Cause of Tides: Centrifugal force due to Earth’s rotation.
  • Syzygy: The alignment of the Sun, Earth, and Moon in a straight line (new moon and full moon). Causes Spring Tides.
  • Conjunction: Sun-Moon-Earth alignment (new moon phase).
  • Opposition: Sun-Earth-Moon alignment (full moon phase).
  • Quadrature: The position where the Sun and Moon are at a right angle to the Earth. Causes Neap Tides.
  • Spring Tides: Highest high tides and lowest low tides; maximum tidal range.
  • Neap Tides: Lowest high tides and highest low tides; minimum tidal range.
  • Semi-diurnal Tide: Two high tides and two low tides per day.
  • Diurnal Tide: One high tide and one low tide per day.
  • UNCLOS: United Nations Convention on the Law of the Sea, 1982, defines maritime zones.
  • Maritime Zone Distances from Baseline:
    1. Territorial Sea: Up to 12 nautical miles (nm).
    2. Contiguous Zone: Up to 24 nautical miles (nm).
    3. Exclusive Economic Zone (EEZ): Up to 200 nautical miles (nm).
  • Innocent Passage: A right for foreign ships to pass through the territorial sea of another state.
  • High Seas: International waters beyond national jurisdiction.
  • International Seabed Authority (ISA): Manages resources of the seabed beyond national jurisdiction (“the Area”).
  • Soil Science Father: Vasily Dokuchaev.
  • Soil Profile: Vertical arrangement of soil horizons.
  • Horizons (top to bottom): O (Organic), A (Topsoil), E (Eluviated), B (Subsoil/Illuviated), C (Regolith), R (Bedrock).
  • Regolith: Layer of unconsolidated weathered rock material above bedrock.
  • Five Factors of Soil Formation (CLORPT): Climate, Organisms, Relief, Parent Material, Time. (Concept by Dokuchaev, refined by Hans Jenny).
  • Eluviation: Washing out of materials from an upper soil horizon.
  • Illuviation: Accumulation of materials in a lower soil horizon.
  • Leaching: Removal of soluble materials from the entire soil profile by water.

Mains Insights

Heat Dome: A Symptom of a Warming World

  • Cause-Effect Relationship (Climate Change): Heat domes are not new phenomena, but their frequency, intensity, and duration are increasing due to anthropogenic climate change. Global warming weakens the temperature gradient between the poles and the equator, which in turn weakens the jet stream, making it more prone to meandering and stalling. This creates a direct link between rising global temperatures and the increased probability of extreme weather events like the 2021 North American heatwave.
  • Socio-Economic Impacts (GS Paper I & III): Such events have devastating consequences. They lead to public health crises (heatstroke, respiratory issues from wildfires), strain on power grids due to increased demand for cooling, agricultural losses from crop failure and livestock death, and severe ecological damage, including mass die-offs of marine life and increased wildfire risk. This highlights the vulnerability of even developed nations to climate extremes.
  • Policy Implications (GS Paper III): The increasing occurrence of heat domes necessitates a shift in policy from mere response to proactive adaptation and mitigation. This includes upgrading infrastructure, developing robust early warning systems, creating public cooling centers, and implementing urban planning strategies like increasing green cover to combat the urban heat island effect, which exacerbates heat domes.

Tides: Resource and Hazard

  • Geopolitical and Economic Significance (GS Paper I & III): The significance of tides extends beyond textbook definitions.
    • Renewable Energy: Tidal energy is a predictable and clean source of power. India has significant potential in the Gulf of Kutch, Gulf of Cambay, and the Sundarbans. Developing this potential can help India meet its renewable energy targets under the Paris Agreement.
    • Coastal Management: Tides are integral to the health of coastal ecosystems like mangroves and estuaries, which act as carbon sinks and biodiversity hotspots. However, the interplay of high tides and rising sea levels due to climate change poses a significant threat of coastal erosion and inundation, impacting coastal communities and livelihoods. This is a key issue in disaster management.
    • Navigation and Trade: Tidal ports remain economically crucial. Understanding tidal patterns is essential for safe navigation and port operations, directly impacting maritime trade and the “Blue Economy.”

Maritime Zones: Arena of Cooperation and Conflict

  • Geopolitical Analysis (GS Paper II): The UNCLOS framework is a cornerstone of international law, but it is also a source of geopolitical friction.
    • Disputes: The South China Sea dispute is a prime example, where China’s “nine-dash line” claim conflicts with the UNCLOS-defined EEZs of several ASEAN nations. Such disputes challenge the rules-based international order.
    • Freedom of Navigation: The concept of “innocent passage” in the territorial sea and “freedom of navigation” in the EEZ is contested. Actions like the US Freedom of Navigation Operations (FONOPs) are intended to challenge what it considers excessive maritime claims, leading to diplomatic tensions.
    • Resource Exploitation: The EEZ gives nations exclusive rights to resources, leading to competition over fisheries and hydrocarbon reserves. The race for deep-sea mining in “the Area,” regulated by the ISA, raises ethical and environmental questions (GS Paper IV) about exploiting the “common heritage of mankind” versus protecting fragile deep-sea ecosystems.

Soil: The Foundation of Civilization

  • Soil as a Critical Resource (GS Paper I & III): The study of soil formation is not merely academic; it is central to understanding human history and contemporary challenges.
    • Historical Perspective: The fertility of soils in river valleys (Nile, Indus) was the foundation of early civilizations. Soil degradation has also been implicated in the decline of civilizations.
    • Contemporary Challenges: Soil degradation (erosion, salinization, desertification) is a major threat to food security, particularly in India. The CLORPT factors show how vulnerable this resource is. For instance, climate change (a change in ‘cl’) is altering rainfall patterns, accelerating erosion. Unsustainable agricultural practices (a change in ‘o’) like overuse of chemical fertilizers are depleting soil health.
  • Ethical and Policy Dimensions (GS Paper III & IV): Protecting soil is an ethical responsibility for intergenerational equity. Policies like India’s Soil Health Card scheme are steps in the right direction, promoting sustainable soil management. Integrating traditional farming knowledge with modern soil science can provide a holistic approach to preserving this vital, non-renewable resource for future generations. The slow nature of soil formation (‘time’ as a factor) underscores the urgency of conservation efforts.

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