Two factors that affect the Earth's crust are temperature and pressure.

• Temperature: Variations in temperature cause expansion and contraction of crustal rocks, leading to weathering and deformation of the crust.
• Pressure: Pressure from overlying rocks, tectonic forces, and magma movement causes the crust to fold, fault, or fracture.

(1) Altitude and (2) monsoon wind (seasonal monsoon).

Altitude determines temperature — temperature falls with height, so a hill area is cooler than the Tarai at the same latitude. The monsoon wind brings heavy summer rainfall, so areas lying in its path (like the Chure/Bhabar and hill slopes) get much more rain than rain-shadow areas like Mustang.

The rock formation process refers to the natural sequence by which rocks are formed and recycled on the Earth's surface and interior. It is best explained through the rock cycle, in which the three major rock types — igneous, sedimentary and metamorphic — are formed from one another. The main processes are:

1. Formation of igneous rocks (cooling and solidification): Molten material called magma (below the surface) or lava (after eruption onto the surface) cools and solidifies. Slow cooling underground forms coarse-grained rocks like granite; rapid cooling on the surface forms fine-grained rocks like basalt. This is the primary or first-formed rock.

2. Formation of sedimentary rocks (deposition, compaction and cementation): Existing rocks are broken down by weathering and erosion into sediments (sand, silt, clay, gravel). These sediments are transported by rivers, wind or glaciers and deposited in layers in low-lying areas, river beds or sea beds. Over time, the weight of overlying layers causes compaction, and dissolved minerals act as cement to bind the grains together through cementation, forming sedimentary rocks such as sandstone, limestone and shale. Fossils are often found in these rocks.

3. Formation of metamorphic rocks (heat and pressure): When igneous or sedimentary rocks are subjected to great heat and pressure deep inside the Earth (or by contact with magma), their minerals recrystallise and their texture and structure change without melting. This process is called metamorphism, producing rocks such as marble (from limestone), slate (from shale) and gneiss (from granite).

4. Recycling (melting and re-solidification): Rocks buried still deeper may melt into magma again, and on cooling form new igneous rocks, completing the cycle. Similarly, any rock may be weathered into sediments to form new sedimentary rocks. Thus the process is continuous and cyclic.

Conclusion: In short, rock formation involves cooling and solidification (igneous), deposition, compaction and cementation (sedimentary), and metamorphism under heat and pressure (metamorphic), all linked in a continuous rock cycle driven by internal and external Earth processes.

Endogenetic forces are the internal forces that originate inside the Earth, mainly from heat and the movement of molten material and crustal plates. They build up and reshape the crust. Their main effects are:

1. Formation of continents and ocean basins: Slow movement of the lithospheric plates (plate tectonics) has divided the crust into continental and oceanic parts, producing the present continents and ocean basins.

2. Formation of mountains: Compressive forces fold and uplift the crust. The Himalaya, formed by the collision of the Indian and Eurasian plates, is a fold mountain; block mountains form where crust is uplifted between faults.

3. Formation of plateaus and plains: Broad upward movement of land forms plateaus (for example the Tibetan Plateau), while sinking or levelling of land forms plains and basins.

4. Folds, faults and rift valleys: Horizontal forces bend rock layers into folds. Tension or compression breaks them along faults, and land sinking between parallel faults forms rift valleys (for example the East African Rift Valley).

5. Volcanic activity: Molten magma rising through weak zones erupts as lava, ash and gases, building volcanic cones, lava plateaus (for example the Deccan Plateau) and islands.

6. Earthquakes: Sudden release of stored stress along faults shakes the ground, causing ground cracks, uplift or subsidence and landslides, as in the 2015 Gorkha earthquake in Nepal.

Conclusion: Endogenetic forces create the major relief of the crust, such as mountains, plateaus, basins and volcanoes, while exogenetic forces later wear these features down.

The climate of a place is the average condition of the atmosphere over a long period. It is never determined by a single cause; several factors act together. The five most important factors influencing climate are described below.

1. Latitude Latitude is the angular distance of a place north or south of the equator. Because the Earth is spherical, the sun's rays fall vertically near the equator and obliquely near the poles. Vertical rays concentrate heat over a small area, so the equatorial belt is hot throughout the year. Oblique rays spread the same energy over a larger area and pass through a greater thickness of atmosphere, so the polar regions remain cold. Thus temperature generally decreases from the equator towards the poles, producing the torrid, temperate and frigid zones. Latitude also controls the length of day and night and the seasonal shift of pressure and wind belts.

2. Altitude Altitude is the height of a place above sea level. Temperature decreases with increasing height at the normal lapse rate of about $6.5^\circ\text{C}$ per 1000 metres, because the atmosphere is heated mainly by terrestrial radiation from below and the air becomes thinner and less able to hold heat at higher levels. Hence hill stations like Nagarkot or Darjeeling are cooler than the Tarai plains at the same latitude, and snow lies permanently on high Himalayan peaks. Altitude also affects air pressure, which falls with height, and influences the amount and form of precipitation on windward and leeward slopes.

3. Distance from the Sea (Continentality) The sea heats and cools slowly, while land heats and cools quickly. Places near the sea therefore enjoy an equable or maritime climate with small annual range of temperature, as in Mumbai or Kochi. Places far inland experience a continental climate with very hot summers and very cold winters, as in Jumla or Delhi. Ocean currents further modify this effect: warm currents raise the temperature of adjoining coasts, while cold currents lower it and often cause fog and desert conditions. Distance from the sea also affects humidity and rainfall.

4. Prevailing Winds and Pressure Belts Winds carry heat and moisture from one region to another. Winds blowing from the sea bring rainfall to coastal areas, while winds blowing from land are dry. The planetary pressure belts and wind systems — the equatorial low, the subtropical highs, the westerlies and the trade winds — determine the seasonal distribution of rainfall. In Nepal, the summer monsoon from the Bay of Bengal brings about 80% of the annual rainfall, while the dry winter monsoon from the north-west brings little rain. Local winds such as the loo, chinook and foehn also affect temperature.

5. Relief and Aspect Mountains act as barriers to winds. A mountain range forces moist air to rise on the windward slope, where it cools, condenses and gives heavy orographic rainfall; the leeward slope remains dry as a rain-shadow area. The Himalaya thus blocks the monsoon from crossing into Tibet and makes the southern slopes of Nepal far wetter than the northern side. Aspect, or the direction in which a slope faces, also matters: south-facing slopes receive more direct sunlight and are warmer than north-facing slopes. Relief further affects temperature through the normal lapse rate and controls the direction of drainage of air masses.

Conclusion Latitude, altitude, distance from the sea, prevailing winds and relief together shape the climate of any region. Their combined effect explains why places on the same latitude can have very different climates, and why Nepal, though small, possesses climates ranging from tropical in the Tarai to alpine in the high mountains.

Soil formation process

Soil formation (pedogenesis) is the slow, gradual transformation of the parent rock material into soil through the combined action of several processes. The main processes are:

1. Weathering of parent rock (disintegration and decomposition). The parent rock is broken down physically by temperature changes, frost, wind and water, and chemically by solution, oxidation, carbonation and hydrolysis. This produces the loose, fine mineral particles that form the skeleton of the soil.

2. Addition of organic matter. Plants, roots, leaves and dead animals fall on the surface and are decomposed by bacteria and fungi, forming humus. Humus gives the soil its dark colour, improves fertility, water-holding capacity and structure.

3. Translocation (eluviation and illuviation). Rainwater percolating downward carries clay, iron, aluminium, lime and humus from the upper layer (eluviation, giving a leached, light-coloured A-horizon) and deposits them in the lower layer (illuviation, forming a clay-rich B-horizon).

4. Horizon development and soil profile. Over time these processes produce distinct layers — O, A, B, C and R horizons — together called the soil profile.

5. Biological activity and mixing. Earthworms, insects, roots and burrowing animals mix organic and mineral matter and aerate the soil, speeding up soil formation.

Conclusion: Soil is thus formed by the interaction of climate, parent rock, relief, organisms and time, with climate and living organisms being the most active factors. The process is very slow — it may take hundreds to thousands of years to form a mature soil profile.

Measures to Protect the Locality from Major Natural Disasters

Nepal is highly prone to natural disasters such as earthquakes, floods, landslides, droughts, and fires. The following measures can protect our locality:

1. Earthquake

• Construct earthquake-resistant buildings using proper pillars, beams, and quality materials as per the building code.
• Conduct public awareness and mock drill programmes so people know to "duck, cover, and hold."
• Keep emergency kits with food, water, torch, and first-aid ready.
• Avoid building houses on steep slopes and loose soil.

2. Flood

• Construct embankments and check dams along rivers.
• Plant trees on riverbanks to control soil erosion.
• Build houses above the flood level and avoid settling on floodplains.
• Develop an early warning system and safe evacuation routes.

3. Landslide

• Afforestation and terracing on vulnerable slopes.
• Construct retaining walls and drainage channels.
• Discourage haphazard road cutting and quarrying on steep hills.
• Shift settlements from high-risk landslide zones.

4. Fire

• Keep fire extinguishers, sand buckets, and water ready.
• Follow safe electrical wiring and cooking practices.
• Conduct awareness campaigns on fire safety.

5. Drought and Other Measures

• Promote rainwater harvesting and irrigation.
• Store food grains and fodder for emergencies.
• Form local disaster management committees and prepare a disaster preparedness plan.
• Coordinate with the local government, Red Cross, and security forces for rescue and relief.

Conclusion: A combination of structural measures (embankments, resistant buildings) and non-structural measures (awareness, early warning, preparedness plans) can greatly reduce the loss of life and property in our locality.

Model Plan to Protect from the Effects of Earthquake

An earthquake cannot be predicted or prevented, but its effects — loss of life, collapse of buildings, fires, landslides and disruption of services — can be greatly reduced by a planned combination of preparedness, engineering and response measures. The following model plan is designed for a disaster-prone settlement or district.

1. Pre-Disaster (Preparedness and Mitigation) Phase

(a) Risk assessment and mapping

• Prepare seismic hazard maps of the area, identifying active fault lines, weak soils and landslide-prone slopes.
• Identify vulnerable structures (old mud-mortar houses, unengineered concrete buildings) and mark safe open grounds for evacuation.

(b) Earthquake-resistant construction

• Enforce the National Building Code in all new construction; use reinforced concrete frames, shear walls, proper foundations and light roofing.
• Retrofitting of existing weak buildings by adding bracing, jacketing columns and tying walls together.
• Follow the "light house, strong base" principle and avoid heavy overhanging structures.

(c) Awareness and education

• Include earthquake safety in school curricula and conduct regular drills (Drop, Cover and Hold On).
• Train masons, engineers and local leaders in safe construction practices.
• Distribute safety information through radio, FM, pamphlets and community meetings.

(d) Institutional and logistic preparation

• Form and train Local Disaster Management Committees, search-and-rescue teams and first-aid groups.
• Stock emergency supplies: food, water, tents, blankets, torches, medicines, shovels and stretchers.
• Prepare emergency communication systems and a warning/drill schedule.

2. During the Earthquake (Response)

• Stay calm; indoors — take cover under a sturdy table, away from windows and heavy objects; outdoors — move to an open area away from buildings, poles and trees.
• Switch off electricity, gas and water mains to prevent fire and electrocution.
• Do not use lifts; do not rush to exits during strong shaking.
• After the shaking stops, evacuate calmly to the pre-identified open ground and take a head count.

3. Post-Disaster (Recovery) Phase

• Conduct rapid search and rescue; provide first aid and shift the injured to hospitals.
• Set up relief camps with safe water, sanitation and food; prevent epidemics.
• Clear debris, restore roads, power, water and communication services.
• Assess damage scientifically and rebuild according to improved seismic codes ("build back better").
• Review the plan after every drill or event and update it.

Conclusion

An effective earthquake protection plan rests on four pillars — hazard mapping, earthquake-resistant construction, public awareness and organised emergency response. If these are implemented together with strict enforcement of building codes and regular mock drills, the loss of life and property from a future earthquake can be minimised substantially.

Permanent Winds and the Origin and Nature of Climate

Permanent winds (also called planetary winds) are the large-scale winds that blow throughout the year in a fixed direction from permanent high-pressure belts to permanent low-pressure belts. Because they are permanent, they become the dominant control of climate over large parts of the earth's surface. Their effect on the origin and nature of climate can be explained as follows:

1. Origin of climate (why a climate type develops where it does):

• The permanent winds originate from the sub-tropical high-pressure belts (blowing towards the equator as trade winds and towards the temperate low-pressure belt as westerlies) and from the polar high-pressure belts (blowing as polar easterlies).
• Where these winds blow from the sea towards land, they carry moisture and give rise to humid, rainy climates; where they blow from land towards sea or from cold to warm regions, they give rise to dry or arid climates.
• Thus the very existence of a particular climate type (equatorial, monsoon, hot desert, temperate, cold) at a place is largely decided by which permanent wind belt that place lies in.

2. Nature of climate (temperature and rainfall characteristics):

• Temperature: Winds blowing from higher (cooler) latitudes to lower (warmer) latitudes cool the place, while winds blowing from lower to higher latitudes warm it. Thus permanent winds decide whether a climate will be cool or warm.
• Rainfall: Winds blowing from ocean to land bring rainfall (maritime influence); winds blowing from land to sea bring dryness (continental influence). The amount and seasonal distribution of rainfall — hence the wet or dry nature of the climate — depends on the direction and moisture content of these winds.
• Humidity and cloudiness: On-shore permanent winds keep the air humid and cloudy; off-shore winds keep it dry and clear.

Effect of one permanent wind with reference to one climate — the Trade Winds and the Equatorial Climate:

The trade winds are permanent winds that blow from the sub-tropical high-pressure belts (about 30° N and 30° S) towards the equatorial low-pressure belt, blowing from the north-east in the Northern Hemisphere (NE trades) and from the south-east in the Southern Hemisphere (SE trades).

• As they blow from the sub-tropics towards the equator, they become increasingly warm and moisture-laden over the oceans.
• On reaching the equatorial belt, the intense heating makes the air converge and rise (the Inter-Tropical Convergence Zone), causing heavy convectional rainfall almost daily.
• This gives the equatorial climate its characteristic nature: uniformly high temperature (about 27°C) throughout the year, very heavy rainfall (over 200 cm), high humidity, and no distinct dry season — the classic hot, wet, ever-green rainforest climate of the Amazon, Congo and Malay Archipelago.
• The same trade winds, when they blow over land in the interior of continents (e.g., the Sahara), lose their moisture and produce hot desert climates, showing that the same permanent wind can create different climates depending on whether it blows over sea or land.

Conclusion: Permanent winds thus act as the primary agent in deciding both the origin (location) and the nature (temperature, rainfall, humidity) of the world's major climatic types.

Natural disasters leave both immediate and long-term marks on the Earth's surface. The main effects are:

1. Changes in landforms

• Earthquakes cause ground rupture, fissures, cracks, and landslides on steep slopes. They may raise or lower land, form fault scarps, and trigger subsidence (land sinking).
• Volcanic eruptions build new landforms such as lava plateaus, cones, and craters, while also destroying existing slopes.
• Landslides remove material from hill slopes and deposit it at the base, changing slope profiles.

2. Soil erosion and deposition

• Floods and landslides strip away fertile topsoil from one place and deposit sand, gravel, and silt elsewhere. Rivers change course and deposit new alluvial plains, sandbars, and deltas.
• Erosion leaves behind gullies, ravines, and barren rocky surfaces.

3. Changes in river courses and drainage

• Floods silt up river beds, shift channels, and create oxbow lakes or new meanders.
• Earthquakes can dam rivers, forming temporary lakes, or cause rivers to disappear underground.

4. Coastal changes

• Tsunamis and cyclones erode beaches, destroy sand dunes, and wash away coastal vegetation.
• They may deposit new sand ridges or shift the shoreline.

5. Glacial and mountain changes

• Avalanches and glacial lake outburst floods (GLOFs) scour valleys, deposit debris, and create new moraines.

6. Destruction of vegetation and fertile land

• Forest fires, floods, and landslides uproot trees and strip vegetation cover, exposing the surface to further erosion.
• Fertile agricultural land is buried under sand or washed away, turning it into waste land.

7. Slope instability

• After an earthquake or heavy rainfall, slopes become weak and prone to repeated landslides and rockfalls for years.

In short, natural disasters reshape the Earth's surface through erosion, deposition, uplift, subsidence, and changes in rivers and coasts, often turning productive land into degraded or unstable terrain.

Metamorphic rocks are rocks formed when existing igneous, sedimentary or older metamorphic rocks are changed in texture, structure and mineral composition by great heat, pressure or chemical action, without melting completely. Examples are marble (from limestone), slate (from shale) and gneiss (from granite).

Four factors controlling weathering are:

1. Climate: temperature and rainfall decide the type and rate of weathering. Hot, humid climates speed up chemical weathering, while frost action dominates in cold areas.
2. Nature of rock: the mineral composition, hardness, joints and cracks of a rock determine how easily it breaks down.
3. Relief (slope): steep slopes remove weathered material quickly, while gentle slopes let it accumulate and weather further.
4. Vegetation and organisms: roots, burrowing animals and decaying plants help break rocks and add organic acids, while a dense plant cover also protects the surface.

Relative humidity is the ratio of the amount of water vapour actually present in the air to the maximum amount the air can hold at the same temperature, expressed as a percentage.

$\text{Relative humidity}=\frac{\text{Actual water vapour content}}{\text{Water vapour capacity at that temperature}}\times 100\%$

When relative humidity reaches 100%, the air is saturated.

The B-horizon is the second layer of the soil profile, lying below the A-horizon and above the C-horizon. It is also called the zone of accumulation or illuviation, because clay, iron and aluminium oxides, lime and some humus washed down from the A-horizon are deposited here. It is therefore compact, contains little organic matter and is usually denser and more reddish or brownish than the layer above.

Two characteristics of monsoon forest are:

1. Deciduous trees: most trees shed their leaves in the dry season to reduce water loss, so the forest looks bare for a few weeks before the rains.
2. Valuable hardwood: the forest is less dense than the equatorial rainforest and has trees of one dominant kind in patches, such as sal, teak and sisam, which give good timber.

Physical geography is the branch of geography that studies the natural features and processes of the Earth's surface and the interaction among them. Its scope is very wide and includes the following fields.

1. Geomorphology: study of the origin, structure and development of landforms such as mountains, plateaus, plains, valleys, and of the processes of weathering, erosion and deposition by rivers, glaciers, wind and waves.
2. Climatology and meteorology: study of the atmosphere, its composition and layers, temperature, pressure, winds, humidity, precipitation, weather and climate, and the classification of world climates.
3. Hydrology and oceanography: study of water on and under the land, rivers, lakes, groundwater, and of oceans, their relief, salinity, tides, waves and currents.
4. Soil geography (pedology): study of the formation, horizons, types, distribution and conservation of soils.
5. Biogeography: study of the distribution of plants and animals, natural vegetation regions and their relation to climate and soil.
6. Astronomical and earth-system aspects: study of the shape, rotation and revolution of the Earth, interior structure, rocks, minerals, earthquakes and volcanoes.
7. Environment and resource management: study of natural hazards such as floods, landslides and drought, climate change, and the sustainable use and conservation of natural resources.

Conclusion: Physical geography explains the natural environment in which humans live, and its knowledge is useful for planning agriculture, settlement, disaster management and environmental conservation.

Sedimentary rocks are formed by the accumulation, compaction and cementation of sediments. On the basis of the process of formation they are of three main types.

1. Mechanically formed (clastic) sedimentary rocks These are formed from fragments of older rocks broken by weathering and erosion, transported by water, wind or ice, deposited in layers, and then compacted and cemented. The rocks differ by the size of the particles.

• Gravel and pebbles form conglomerate.
• Sand forms sandstone.
• Silt and clay form shale and mudstone.

2. Organically formed sedimentary rocks These are formed from the remains of plants and animals that accumulate and harden over a long time.

• Shells and skeletons of marine organisms form limestone (organic).
• Buried vegetation forms coal and peat.

3. Chemically formed sedimentary rocks These are formed when dissolved minerals in water precipitate out or when water evaporates, leaving the minerals behind.

• Evaporation of sea water or lakes forms rock salt and gypsum.
• Chemical precipitation of calcium carbonate forms some limestone and dolomite.

Common features: These rocks occur in layers (strata), often contain fossils, and are generally softer than igneous rocks. Because they are formed in layers over millions of years, they preserve the history of past environments.

Transportation is the carrying of eroded material (the load) by a river from one place to another. The river transports its load in the following ways.

1. Solution: soluble minerals such as calcium carbonate and salts are dissolved in the water and carried invisibly. This is common in rivers flowing over limestone.
2. Suspension: very fine particles of clay and silt are lifted by turbulence and carried within the flowing water, giving a muddy appearance, especially during floods.
3. Saltation: medium-sized particles such as sand and fine gravel are lifted for short distances, then fall back and bounce along the bed in a series of jumps.
4. Traction: large and heavy materials such as pebbles, cobbles and boulders are rolled, dragged or slid along the river bed. They move mainly during floods.

Factors affecting transportation: the volume and velocity of water, the gradient of the bed and the size and weight of the load. A swift and large river carries a bigger load. When the velocity falls, the river drops its load, beginning with the heaviest, and this results in deposition and the formation of features such as deltas and flood plains.

The normal cycle of erosion, proposed by W. M. Davis, describes the stages by which a land area uplifted above sea level is gradually worn down by running water to a low, almost flat surface. It has three stages.

1. Youthful stage

• The rivers have a steep gradient and high velocity, so vertical erosion (downcutting) dominates.
• Deep, narrow V-shaped valleys, gorges, canyons, rapids and waterfalls develop.
• Valleys are separated by wide, flat interfluves, and there are few tributaries. Lakes and marshes may be present.

2. Mature stage

• The gradient becomes gentler, and downcutting slows while lateral (side) erosion increases.
• The valley is widened, and the river develops many tributaries, a well-integrated drainage system and a developed flood plain.
• Waterfalls and rapids are smoothed out, and the river begins to form meanders. Relief is at its maximum.

3. Old stage

• The gradient is very low, and deposition exceeds erosion.
• The river forms wide meanders, ox-bow lakes, a broad flood plain, natural levees and, near the sea, a delta.
• Hills are reduced and the land is lowered to a nearly flat surface called a peneplain, with isolated resistant hills called monadnocks.

Conclusion: Thus the river changes the land from a high, rugged surface to a plain, passing through youth, maturity and old age.

Meaning (2 marks): Moraine is the rock debris, such as clay, sand, gravel and boulders, that is eroded, carried and deposited by a glacier. When the ice melts, this unsorted and unlayered material is left behind in ridges or mounds.

Types of moraine (3 marks): Moraines are classified by their position.

1. Lateral moraine: ridges of debris formed along the sides of a valley glacier, mainly from material fallen from the valley walls.
2. Medial moraine: a ridge formed in the middle of a glacier when the lateral moraines of two glaciers join at their meeting point.
3. Ground moraine: a thick layer of unsorted debris dragged along the base of the glacier and spread over the valley floor when the ice melts, forming undulating plains.
4. Terminal (end) moraine: a curved ridge of debris deposited at the snout of the glacier where it stops advancing. It marks the furthest extent of the glacier.

Weather and climate both describe the condition of the atmosphere, but they differ in the following ways.

In short, weather is the day-to-day condition of the atmosphere, while climate is the long-term average of weather.

Factors affecting the distribution of temperature (3 marks)

1. Latitude
2. Altitude
3. Distance from the sea (land and water distribution)
4. Ocean currents
5. Prevailing winds
6. Slope and aspect of land
7. Cloudiness and rainfall
8. Nature of the surface and vegetation cover

Explanation of one factor: Latitude (2 marks) Latitude is the angular distance of a place from the equator. Near the equator the Sun's rays fall almost vertically, so a small area receives concentrated heat and the rays pass through a thinner layer of atmosphere. Towards the poles the rays are oblique, so the same energy is spread over a larger area and passes through a thicker atmosphere. Hence temperature decreases from the equator towards the poles, which gives the torrid, temperate and frigid zones.

Meaning Cyclonic (frontal) rainfall occurs when warm, moist air meets cold, dense air along a front, usually in a low-pressure system called a cyclone. It is common in the temperate latitudes, where it is also called frontal rainfall, and in tropical cyclones.

Process

1. In a cyclone, air from different regions converges towards a low-pressure centre.
2. When a warm, moist air mass meets a cold air mass, the lighter warm air rises over the denser cold air along the sloping front.
3. As it rises, the warm air cools adiabatically, and the water vapour condenses to form clouds.
4. Further condensation produces rain, which is usually widespread and continuous, lasting for days.

Diagram (described) Draw a cold air mass on the left as a wedge with its sloping surface, and a warm, moist air mass on the right. Show arrows of warm air rising along the slope above the cold air, with clouds and rain falling along and ahead of the front.

Importance and example It brings rain to much of western Europe and to the western Himalaya of Nepal in winter, through the western disturbances.

Podzolization is the soil-forming process that occurs in cool, humid (cold temperate) climates under coniferous forest, where leaching of the upper soil is very strong. It produces the podzol soil, also called an ash-grey soil.

Conditions

• Cool temperature with high rainfall or snowmelt.
• Coniferous vegetation, whose needle litter decays slowly and produces acidic humus.
• Sandy, well-drained parent material.

Process

1. Needle litter from coniferous trees decomposes slowly and forms organic acids, which make the soil strongly acidic.
2. The rainwater percolating down becomes acidic and dissolves iron, aluminium and other minerals. This downward washing is called eluviation or leaching.
3. The upper layer (A-horizon) is stripped of these minerals and bases and is left with silica, so it becomes light grey and ash-like, with a bleached E-layer.
4. The dissolved iron, aluminium and humus are carried down and deposited in the B-horizon (illuviation), which becomes dark and sometimes hardened into a layer called hardpan.

Result The soil has a thin organic layer, a grey leached upper layer and a darker accumulation layer below. It is acidic, poor in nutrients and not very fertile, so it is of limited use for agriculture. It is found in Siberia, northern Europe and Canada, and in parts of the high Himalaya.

On the basis of the moisture available, natural vegetation is classified into the following types.

1. Hydrophytes These plants grow in water or in very wet places. Their leaves and stems have air spaces that help them float or breathe. Examples: water lily, lotus, water hyacinth and algae.

2. Xerophytes These plants are adapted to dry, desert conditions with very little water. They have long roots, thick fleshy stems, small or no leaves (spines) and a waxy coating to reduce water loss. Examples: cactus, acacia and date palm.

3. Mesophytes These plants grow in areas of moderate moisture. They have broad leaves and a well-developed root system. Most trees, crops and forests of the temperate and monsoon regions belong here, such as sal, teak, mango and wheat.

4. Tropophytes These plants are adapted to areas that have alternate wet and dry seasons. They behave as mesophytes in the wet season and as xerophytes in the dry season, shedding their leaves in the dry season. Examples: deciduous trees such as sal and sisam of the monsoon forest.

5. Halophytes These plants grow in saline soils and coastal salt marshes. Examples: mangroves.

An earthquake is the sudden shaking of the ground caused by the release of energy in the Earth's crust. Earthquakes are not distributed evenly over the world but occur mainly along the boundaries of the tectonic plates, where stress builds up. The world's earthquake belts are as follows.

1. Circum-Pacific belt (Ring of Fire)

• This is the most active belt and has about 80% of the world's earthquakes.
• It surrounds the Pacific Ocean, running along the western coast of North and South America (Alaska, California, Mexico, Chile and Peru), then through the Aleutian Islands, Kamchatka, Japan, the Philippines, Indonesia and New Zealand.
• It is formed by subduction of the Pacific and other oceanic plates beneath continental plates and is also the main zone of volcanoes.

2. Mid-Continental (Alpine-Himalayan) belt

• It has about 15% of the earthquakes.
• It runs from the Mediterranean region (Spain, Italy, Greece, Turkey) through Iran, the Hindu Kush and the Himalaya, including Nepal, to Myanmar and Indonesia, where it joins the Pacific belt.
• It results from the collision of the Eurasian plate with the African and Indian plates. The 2015 Gorkha earthquake of Nepal belongs here.

3. Mid-Atlantic ridge belt

• It extends along the Mid-Atlantic Ridge in the Atlantic Ocean from Iceland southwards.
• It is related to plate divergence, where new crust forms, and earthquakes are mostly shallow and of low to moderate magnitude.

4. Other zones

• The East African Rift Valley, a region of plate divergence, and the Mid-Indian Ocean ridge also have frequent earthquakes.
• Intraplate earthquakes occur occasionally away from plate boundaries along old faults.

Sketch map (described) On an outline world map, draw a thick line for the Circum-Pacific belt around the Pacific Ocean, a line for the Alpine-Himalayan belt from the Mediterranean to Indonesia, and a line down the middle of the Atlantic Ocean for the Mid-Atlantic ridge belt. Label Nepal, Japan, Chile and California.

Meaning (3 marks) A plateau is an extensive, elevated, flat-topped landform that rises sharply above the adjoining land on at least one side, usually with steep slopes. Its height is generally more than 300 metres above the surrounding area. Examples are the Tibetan Plateau, the Deccan Plateau and the Colorado Plateau.

Classification on the basis of formation (5 marks) Plateaus are of three main types according to their mode of formation.

1. Tectonic plateaus: formed by the uplift of land by endogenetic forces such as crustal folding and faulting.
2. Volcanic (lava) plateaus: formed by the spreading and cooling of lava from fissure eruptions.
3. Erosional (residual) plateaus: formed when running water, glaciers or wind erode the surrounding area and leave a flat, elevated block.

Description (4.5 marks)

1. Tectonic plateaus These are of two kinds.

• Intermontane plateaus are surrounded by mountain ranges and are formed by mountain-building forces. Examples: Tibetan Plateau and the plateau of Bolivia.
• Continental plateaus are formed by uplift of a large part of the continent or are bordered by plains or the sea. Examples: the plateaus of Africa, Arabia and the Deccan.

2. Volcanic plateaus Fissure eruptions of basaltic lava flood a wide area, and successive flows build a thick, flat plateau. Examples: the Deccan Trap of India, the Columbia Plateau of the USA and the plateau of Iceland.

3. Erosional plateaus Rivers cut deep valleys into an uplifted area, leaving flat-topped remnants, or glaciers and wind remove softer rocks. Examples: the Colorado Plateau, with the Grand Canyon, and the Appalachian Plateau.

Plateaus are important for mining, grazing, hydropower and agriculture on fertile lava soils, such as the black cotton soil of the Deccan.

Classification of world climate (5 marks) Several scientists have classified world climates; the widely used scheme is that of Koppen, based on temperature and precipitation, with vegetation as an indicator. It divides the world into five major groups:

1. A: Tropical humid (hot) climates: every month is above 18 degrees C. Types: equatorial rainforest (Af), tropical monsoon (Am), savanna (Aw).
2. B: Dry climates: evaporation exceeds precipitation. Types: desert (BW) and steppe (BS).
3. C: Warm temperate (mesothermal) climates: the coldest month is between 0 and 18 degrees C. Types: Mediterranean (Cs), humid subtropical (Cfa, Cwa) and marine west coast (Cfb).
4. D: Cold snowy (microthermal) climates: the coldest month is below 0 degrees C. Types: humid continental and subarctic (taiga).
5. E: Polar climates: every month is below 10 degrees C. Types: tundra (ET) and ice cap (EF).

Highland climates (H) are sometimes added as a sixth group.

Equatorial climate (5 marks)

• Location: within about 5 to 10 degrees north and south of the equator. It covers the Amazon basin of South America, the Congo basin of Africa and the islands of Indonesia and Malaysia.
• Temperature: high throughout the year, with a mean monthly temperature of about 27 degrees C and a very small annual range of 2 to 3 degrees C. Nights are warm and humid.
• Rainfall: heavy, usually 200 cm or more, spread through the year with no dry month. It is mostly convectional, falling in the afternoon with thunder and lightning.
• Humidity and winds: the air is humid and sultry, and winds are light (the doldrums).
• Vegetation: dense, evergreen tropical rainforest with tall, broadleaved trees in layers, such as mahogany and ebony, and thick undergrowth.
• Life: diverse wildlife, with sparse population and traditional shifting cultivation; the climate is unhealthy and enervating.

Map (2.5 marks, described) On a world outline map, shade a belt about 10 degrees on either side of the equator, covering the Amazon basin, the Congo basin and Southeast Asian islands, and label it "Equatorial climate".