A delta is a triangular tract of alluvium deposited at the mouth of a river where it enters a sea or lake, formed when the river's load settles faster than it can be carried away by tides and waves.

Tropical rainforest (evergreen forest) and tropical monsoon (deciduous) forest.

These are the two main vegetation types of the tropical climate region — the equatorial belt receives heavy rainfall throughout the year and supports dense evergreen rainforest, while the monsoon belt has a marked dry season and supports deciduous forest.

Mountain Formation Process

Mountains are formed mainly by tectonic forces acting on the Earth's crust over millions of years. The process can be explained in the following steps:

1. Plate movement: The Earth's crust is divided into several large and small tectonic plates that float over the semi-molten asthenosphere. Convection currents in the mantle cause these plates to move slowly.

2. Convergence and collision: When two plates move towards each other (convergent boundary), several situations arise:

   • Ocean–continent convergence: The denser oceanic plate subducts beneath the lighter continental plate. The subducted plate melts, and the molten material rises to form volcanic mountains (e.g., the Andes).
   • Continent–continent convergence: When two continental plates collide, neither subducts easily because both are light. The crust crumples, folds, and thickens, pushing up high fold mountains (e.g., the Himalayas formed by the collision of the Indian and Eurasian plates).

3. Folding and upliftment: The compressional force squeezes the sedimentary rocks deposited in geosynclines, causing them to fold into anticlines and synclines. Continued pressure raises these folded rocks into high mountain ranges.

4. Faulting and block mountains: Sometimes, instead of folding, the crust breaks along faults. The uplifted block forms block mountains (horsts), and the sunken part forms rift valleys (e.g., the Vosges and Black Forest).

5. Volcanic activity: Magma rising through cracks and vents cools and solidifies on the surface, building volcanic mountains (e.g., Mount Fuji, Mauna Kea).

6. Erosion and shaping: After formation, agents like water, wind, and ice erode the mountains, giving them their present shape and height.

Thus, mountain formation is a continuous geomorphic process driven by endogenetic forces (plate movement, folding, faulting, volcanism) and modified by exogenetic forces (erosion and weathering).

Glaciers build landforms by depositing the rock debris (moraine) they carry when they melt and retreat. These are called glacial depositional landforms. The main structures are:

1. Moraines — ridges of unsorted rock debris left by a glacier.

• Terminal (end) moraine: a crescent-shaped ridge across the valley at the farthest point reached by the glacier.
• Lateral moraine: debris deposited along the two sides of the valley.
• Medial moraine: debris carried in the middle where two glaciers meet.
• Ground moraine: a sheet of debris spread over the valley floor as the ice melts.

2. Drumlins — smooth, oval-shaped mounds of till (boulder clay) with a steep side facing the direction of ice movement and a gentle lee side. They often occur in groups called "basket-of-eggs" topography.

3. Eskers — long, winding ridges of sand and gravel deposited by meltwater streams flowing under or inside the glacier.

4. Kames — small, irregular mounds of sand and gravel dropped by meltwater at the edge of the glacier.

5. Kettle holes — depressions formed when a block of buried ice melts, often filled with water to form kettle lakes.

6. Outwash plains — broad, flat plains of sorted sand and gravel spread by meltwater beyond the terminal moraine.

7. Erratics — large boulders carried far from their place of origin and left on a different rock type when the ice melts.

These features are best developed in high-latitude and high-mountain regions, and their study helps reconstruct the extent and direction of past glaciation.

Functions of a River (5 marks)

A river performs several important functions in nature, which can be grouped as follows:

1. Erosion: A river wears away and cuts the land surface along its course through the processes of hydraulic action, abrasion, attrition and solution. It carries away soil and rock material from the upper course, forming valleys, gorges and canyons.

2. Transportation: The eroded materials (load) are carried downstream in solution, suspension, saltation and traction. In this way the river transports sediments from highlands to lower plains and seas.

3. Deposition: When the velocity of the river decreases, especially in the lower course, plains, deltas and floodplains, it deposits its load. This forms fertile alluvial plains, deltas, sandbars, ox-bow lakes and levees.

4. Drainage and water supply: A river drains excess water from its catchment area, preventing waterlogging, and supplies water for drinking, irrigation, industry, navigation and hydroelectricity generation.

5. Modification of landforms and ecology: By continuous erosion and deposition, a river shapes the earth's surface (V-shaped valleys, meanders, waterfalls, deltas) and supports rich aquatic and riparian ecosystems, besides moderating local climate and recharging groundwater.

In short, a river acts as an agent of erosion, transportation and deposition, a source of water and energy, and a major sculptor of the earth's surface.

Climate change refers to the significant and long-term change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. In the modern context, it means the persistent alteration of the Earth's climate system — mainly a rise in average global temperature (global warming) — caused largely by human activities.

Key points:

• Definition: Climate change is the long-term shift in temperature, precipitation, wind patterns, and other measures of climate lasting for an extended period (usually 30 years or more).
• Natural causes: Volcanic eruptions, changes in solar radiation, variations in Earth's orbit (Milankovitch cycles), and natural greenhouse gas emissions.
• Anthropogenic (human) causes: Burning of fossil fuels (coal, petroleum, natural gas), deforestation, industrialisation, and agriculture, which increase greenhouse gases (CO₂, CH₄, N₂O, CFCs) in the atmosphere.
• Greenhouse effect: These gases trap outgoing infrared radiation, raising the Earth's surface temperature — the enhanced greenhouse effect.
• Evidence: Rising global mean temperature, melting glaciers and polar ice, rising sea level, more frequent extreme events (floods, droughts, cyclones), and shifting monsoon patterns.
• Impacts in Nepal: Glacier retreat in the Himalaya, increased risk of glacial lake outburst floods (GLOFs), erratic rainfall, landslides, and threats to agriculture and biodiversity.
• Response: Mitigation (reducing emissions, afforestation, renewable energy) and adaptation (disaster preparedness, climate-resilient farming), along with international efforts like the UNFCCC and the Paris Agreement.

In brief, climate change is the long-term, largely human-induced alteration of global and regional climate, with far-reaching environmental, economic and social consequences.

Causes of Soil Degradation

Soil degradation is the decline in soil quality, fertility and productive capacity caused by both natural processes and human activities. Its major causes are:

1. Deforestation. The removal of forest cover exposes the soil surface to rain and wind. Without roots to bind the particles and litter to protect the surface, topsoil is easily washed or blown away. In Nepal, heavy felling in the Chure and Middle Hills has accelerated this process.

2. Overgrazing. When too many livestock graze on limited land, vegetation is eaten before it can regenerate. The trampling of hooves compacts the soil, reduces infiltration and leaves the surface bare to erosion. This is a serious problem in the rangelands of the Himalaya and the Chure.

3. Unscientific farming practices. Continuous cropping without fallow or rotation, excessive use of chemical fertilizers and pesticides, and monoculture deplete nutrients and destroy soil structure and micro-organisms. Farming on steep slopes without terracing accelerates the loss of topsoil.

4. Improper irrigation and waterlogging. Over-irrigation and poor drainage raise the water table, causing waterlogging. Evaporation then leaves salts behind, producing salinity and alkalinity that make the soil unfit for cultivation. This is common in parts of the Tarai.

5. Slope and rugged topography. Steep gradients increase the velocity of runoff, so soils on hill slopes are naturally prone to erosion. The fragile geology of the Himalaya, with weak, unconsolidated rocks, adds to the problem.

6. Natural factors. Heavy monsoon rainfall, landslides, floods, earthquakes and strong winds remove or bury fertile topsoil. Nepal's concentrated monsoon, with most rain in a few months, makes this especially severe.

7. Construction and urbanization. Roads, buildings and other infrastructure disturb the soil, remove vegetation and create steep cut slopes and spoil heaps that are easily eroded. Unplanned road building in the hills is a major cause of landslides.

8. Mining and quarrying. Extraction of sand, gravel and minerals from riverbeds and hillsides destroys the soil cover and destabilizes slopes.

9. Land use change and pollution. Conversion of forest and farmland to other uses, plus industrial waste, sewage and solid waste, contaminate the soil and reduce its biological activity.

Measures for Soil Conservation

1. Afforestation and reforestation. Planting trees on bare and degraded land binds the soil with roots, checks runoff and restores organic matter. Community forestry in Nepal is a successful model of this approach.

2. Terracing and contour farming. Terrace farming on hill slopes reduces the speed of runoff and retains water and soil. Contour ploughing, strip cropping and alley cropping along contour lines serve the same purpose on gentler slopes.

3. Controlled grazing. Limiting the number of livestock, rotational grazing and stall feeding allow vegetation to recover and prevent compaction and trampling.

4. Scientific farming. Crop rotation, mixed cropping, use of green manure and compost, and balanced use of chemical fertilizers maintain fertility and soil structure. Organic farming should be encouraged.

5. Check dams and gully control. Building check dams, brush dams and embankments in gullies and rivers traps sediment and prevents further cutting of the land.

6. Proper irrigation and drainage. Regulated irrigation with adequate drainage prevents waterlogging and salinity. Sprinkler and drip irrigation save water and reduce salt accumulation.

7. Watershed management. Treating an entire watershed — its slopes, streams and land — through integrated planning conserves soil and water together. Nepal's watershed management projects follow this approach.

8. Land use planning. Land should be used according to its capability: steep slopes for forest, moderate slopes for pasture and terraced farming, and flat land for intensive agriculture.

9. Control of construction and mining. Roads and buildings should be built with proper engineering, slope protection and bio-engineering measures. Sand and stone extraction from rivers should be regulated.

10. Awareness and legal measures. Public awareness, environmental education and strict enforcement of laws on forest, land and environment are essential for long-term soil conservation.

In short, soil degradation in Nepal results mainly from deforestation, overgrazing, unscientific farming and unplanned construction on fragile slopes. Conservation requires a combination of biological measures (afforestation, cropping practices), engineering measures (terraces, check dams, drainage) and institutional measures (land use planning, laws and awareness), applied together on a watershed basis.

Interrelationship between Climate and Vegetation of Nepal

Introduction

Climate and vegetation are two closely related components of the natural environment. Climate determines the type and density of vegetation, while vegetation also influences climate by affecting temperature, humidity and rainfall. Nepal, extending from the Terai (about 60 m) to the Himalaya (above 8,000 m), shows a great variety of climate and vegetation, and the two are directly interrelated.

Effect of Climate on Vegetation

1. Temperature and altitude: As altitude increases, temperature decreases at about 6.5°C per 1,000 m. This produces distinct vegetation belts:

   • Tropical zone (Terai and Chure, below 1,000 m): hot and humid climate with heavy rainfall; dense tropical evergreen forests of sal, sisau, khair, simal and tall grasses.
   • Subtropical zone (1,000–2,000 m): warm temperate climate; forests of chilaune, katus, sal, bamboo and schima.
   • Temperate zone (2,000–3,000 m): cool climate; oak, rhododendron, maple, walnut, pine and fir.
   • Sub-alpine zone (3,000–4,000 m): cold climate; coniferous forests of spruce, fir, birch, juniper and rhododendron.
   • Alpine zone (4,000–5,000 m): very cold, short growing season; only mosses, lichens, dwarf shrubs and alpine pastures (kharka).
   • Above 5,000 m: perpetual snow; no vegetation.

2. Rainfall: Vegetation is dense where rainfall is high (eastern Nepal, more than 2,000 mm) and sparse where rainfall is low (Manang, Mustang, less than 500 mm). The rain-shadow areas beyond the Himalaya have a dry, desert-like climate with thorny bushes and cactus.

3. Wind and sunlight: Strong winds and steep slopes in high mountains limit the growth of tall trees. Sunny slopes have more vegetation than shady slopes at the same altitude.

Effect of Vegetation on Climate

1. Rainfall: Forests release water vapour through transpiration, which increases humidity and helps in rainfall. Deforestation in the Chure and Terai has reduced local rainfall and increased drought.
2. Temperature: Forests keep the local climate cool by absorbing carbon dioxide and giving shade. Clearing forests makes the climate hotter.
3. Soil and water: Roots hold soil and help water to seep into the ground, which maintains springs and streams and keeps the local climate moist.
4. Windbreak: Trees reduce the speed of hot and cold winds, making the local climate moderate.

Conclusion

Thus, climate and vegetation of Nepal are interdependent: climate decides the type and distribution of vegetation from Terai to Himalaya, and vegetation in turn maintains rainfall, temperature and moisture. Therefore, protection of forests is necessary to keep the climate balanced.