6th Class Geography Unit 6 Changing Earth and Human Activities MCQs | PAKMCQs

Landforms are in a state of continuous change because rocks are constantly broken down and reshaped by internal forces (like tectonics) and external forces (like wind and water).

Tectonic activity originates within the Earth's interior and acts as a powerful internal geological force.

Wind and water are prime examples of external agents operating on the surface of the Earth.

Weathering and erosion are the fundamental natural processes responsible for breaking down rocks and reshaping landscapes.

Weathering is the in-situ (in place) disintegration and decomposition of rocks on the Earth's surface by natural agents.

Weathering breaks rocks down without transporting them away ("in its place"), whereas erosion actively carries the particles away.

Weathering is divided into three distinct types: physical, chemical, and biological weathering.

In physical weathering, rocks are mechanically fractured into smaller fragments while retaining their original chemical makeup.

Physical weathering is also known as mechanical weathering.

When water trapped in fissures freezes, its volume expands by roughly 9%, exerting immense pressure that shatters the rock.

Areas with diurnal temperature swings crossing 0°C (mountains and periglacial zones) experience frequent freeze-thaw weathering.

Chemical weathering involves chemical alterations where original rock minerals react with environmental substances to form new compounds.

Chemical weathering is also known as rock decomposition because it breaks down the rock's chemical structure.

Limestone caverns and subterranean cave systems worldwide are created through the chemical dissolution of calcium carbonate by carbonic acid.

Oxygen (oxidation) and carbon dioxide dissolved in water (carbonation) are the primary gaseous agents of chemical weathering.

Biological weathering occurs due to the mechanical and chemical actions of living organisms (flora and fauna).

Because it is driven by living (organic) matter, biological weathering is also termed organic weathering.

As tree roots expand within small fissures, they exert tremendous outward wedging pressure that splits hard rock apart.

Burrowing creatures (rodents, rabbits, insects) excavate subsoil, fracturing weathered rocks and exposing fresh rock to surface agents.

Erosion is the physical detachment, cutting, and transportation of weathered rock materials by mobile natural agents like water, wind, or ice.

The three chief moving agents responsible for geographic erosion are wind, flowing water, and glacial ice.

Wind erosion involves the detachment, lifting, and transport of loose dust, silt, and sand grains across landscapes.

Wind erosion is most aggressive in arid, flat, and desert environments where vegetation is scarce and loose particles are easily lifted.

In the 1930s ("Dust Bowl"), severe drought and wind erosion stripped millions of tons of fertile topsoil across the US Great Plains.

Wind transports fine, nutrient-rich silt over great distances and deposits it in thick layers called loess, which forms exceptionally fertile soils.

China's Yellow River basin contains extensive, fertile loess plateaus built up over millennia by wind-borne desert dust.

Fast-flowing water (in channels, overland sheets, and coastal waves) is the most powerful and pervasive agent shaping landscapes.

Flowing water exerts hydraulic force and carries abrasive sediments that scour streambeds, riverbanks, and valleys.

The Swat valley was carved out over long periods by the erosive downward cutting of the River Swat.

The Grand Canyon of the Colorado River is an awe-inspiring, massive chasm carved by millions of years of river water erosion.

Glacial erosion occurs exclusively in freezing cold environments and high-altitude alpine zones where perennial snow forms glaciers.

Moving masses of glacial ice bulldoze valleys into broad U-shapes, sharpen peaks into horns, and leave depressions that become lakes.

Khaplu valley in Gilgit-Baltistan exhibits prominent erosional landforms created by ancient glacial action.

Mass wasting refers to the downslope movement of rock, regolith, and soil driven directly by gravitational pull.

Mass wasting is a major form of denudation (the progressive lowering and wearing away of the Earth's surface).

Earth tremors, saturating rains, deforesting slopes, and artificial cutting into hillsides destabilize slopes, triggering landslides.

Half of mankind resides within coastal belts, which handle 90% of global commerce, major fisheries, and tourism.

The concept of the 'Blue Economy' harnesses ocean and coastal resources sustainably for economic prosperity.

According to the World Bank, the Blue Economy is the sustainable use of ocean resources for growth, jobs, and healthy marine ecosystems.

Four primary hydraulic processes drive marine erosion: hydraulic action, attrition, abrasion, and solution.

Hydraulic action is the sheer mechanical force of crashing waves trapping and compressing air into rock cracks, causing rock collapse.

Wave impact directly strikes the cliff foot, opening up wave-cut notches and undermining the structure.

Attrition occurs when loose rock fragments knocking against each other in the surf become smaller, rounded, and smooth.

Continuous collision grinds down sharp edges, turning rough fragments into smooth, rounded beach shingles and sand grains.

Abrasion is the abrasive sandpaper effect when waves throw suspended pebbles and sand against rock walls, carving them away.

Abrasion grinds and smooths rock surfaces just like sandpaper scouring wood.

Solution occurs when weak carbonic acid in seawater chemically dissolves soluble minerals like calcium carbonate in limestone cliffs.

Limestone consists of calcium carbonate, which dissolves readily when attacked by salty, mildly acidic sea water.

Marine erosion sculpts distinctive landforms including sea cliffs, wave-cut platforms, headlands, caves, natural arches, and stacks.

A cliff is a steep, often nearly vertical rock face overlooking the ocean, carved by wave erosion at its base.

Waves erode weaker rock at the water line; as the base is undermined, overlying rock collapses, leaving a sheer cliff face.

A wave-cut platform is a relatively flat bench of solid rock exposed at low tide, created as a sea cliff retreats landward.

Repeated undercutting causes cliff collapse; the remaining smoothed rock base is revealed as a wave-cut platform.

A headland is a promontory of tough, erosion-resistant rock jutting out prominently into the ocean.

Differential erosion wears away softer strata quickly (forming bays), while bands of hard rock resist erosion and project out as headlands.

Waves concentrate hydraulic energy on faults or lines of weakness on a headland, eroding them into deep hollow caves.

A sea arch forms when two back-to-back caves unite or waves blast through a narrow headland, creating an open bridge.

An arch consists of a solid rock roof spanning across two ocean-facing side buttresses.

When wave erosion and gravity cause the unsupported roof of a sea arch to collapse, an isolated column of rock—a stack—is left standing.

Wave erosion expands a crack into a cave; opposite caves cut through to form an arch; when the arch roof falls, a stack remains.

Human activities—namely deforestation, intensive tillage, open mining, and urbanization—are the primary drivers of rampant soil erosion.

Human land modifications accelerate soil erosion by roughly ten times compared to natural rates.

Tree roots physically bind soil crumbs and tree foliage softens raindrops; when cleared, soil washes away easily.

Population growth fuels clearing forests for cropland, firewood, paper pulp, housing, and factories.

Without leaf litter to replenish humus, the soil's organic structure breaks down and valuable nutrients are depleted.

Afforestation is universally recognized as the most effective natural defense to stabilize topsoil and halt erosion.

Ploughing overturns and shatters soil aggregates, leaving bare loose soil vulnerable to being swept away by rains and gales.

Topsoil holds nearly all organic matter and biology; its removal severely impairs crop yields and natural soil regeneration.

Over-application of chemical fertilizers and pesticides kills soil microorganisms, acidifies earth, and ruins soil structure.

Unsustainable intensive farming combined with the wholesale clearance of surrounding forests leads to desertification.

Heavy machinery bulldozes natural vegetation, alters natural drainage, and strips ground cover to make way for plants and roads.

Open-cast mining strips off overlying earth, blasts bedrock, and leaves heaps of loose tailings that wash away in heavy rain.

Paper mills and commercial timber lumbering demand millions of felled trees, stripping hillsides and accelerating erosion.

Urbanization is the demographic shift involving mass migration of rural populations into expanding towns and cities.

According to the United Nations, more than 50% of mankind now resides in urban agglomerations.

Ground clearance for urban sprawl strips stabilizing grass and trees; bulldozed construction sites wash away during rains.

Concentrated vehicular emissions, sewage, and concrete cover sharply degrade urban air, soil, and water quality.

Urban sprawl encroaches upon prime arable fields, turning productive food-growing soils into concrete parking lots and housing.

Field-edge shelterbelts break the mechanical force of surface winds and anchor border soils against washing away.

Controlling livestock numbers gives grassland vegetation time to regenerate, ensuring the soil remains covered and anchored.

Cutting hillside slopes into stepped terraces reduces runoff speed, allowing water to soak in rather than strip topsoil.

Engineered retaining walls offer physical resistance that holds back unstable hillsides and prevents mass movements.

Standardized mining practices prevent tunnel collapse, reduce spoil heaps, and stabilize surrounding terrains.

Human civil engineering reshapes terrain by flattening hills, driving highway tunnels, building bridges, and reclaiming coasts.

Building artificial harbors, jetties, sea walls, and filling shallow waters to expand cities alters coastlines drastically.

Paved urban surfaces create an impermeable shield; instead of soaking in to replenish aquifers, rainwater runs off into storm drains.

A celebrated natural sea arch at Hawkes Bay near Paradise Point, Karachi, collapsed under wave erosion and human impacts.

Continuous hydraulic wave battering weakened the arch until tourist trampling and human interference triggered its structural collapse.

Afforestation is the deliberate planting of new forests on previously non-forested, empty, or barren land.

A burrow is an underground tunnel or hole excavated by small creatures for shelter.

Denudation encompasses all processes (weathering, erosion, mass wasting) that strip rock layers and lower the elevation of landforms.

Desertification is severe environmental degradation stripping land of its organic fertility until it becomes unproductive desert.

Loess is an extensive deposit of windblown, highly fertile silt dust.

Pebbles are small, water-worn, smoothed and rounded rock fragments found on stream beds or sea shores.

Sediments are mineral fragments, sand, silt, and organic particles that sink and settle at the bottom of liquids or water bodies. Exercise

Physical weathering is also called mechanical weathering because rocks are broken down into smaller pieces through mechanical processes without any change in their chemical composition.

According to the United Nations, more than half (around 55%) of the global population currently resides in urban areas.

Minerals present within rocks undergo chemical reactions with atmospheric water, oxygen, and carbon dioxide, leading to chemical weathering.

Wind erosion is most dominant in dry (arid and semi-arid) areas where loose soil and lack of dense vegetation allow winds to transport particles easily.

Sea waves are the primary force driving coastal erosion through hydraulic action and abrasion along coastlines.

The Swat Valley has been primarily shaped and carved out by fluvial (water) erosion through the action of the Swat River.

Glaciers only exist and flow in cold, high-altitude or polar regions where temperatures remain below freezing.

Continuous pounding and hydraulic pressure from sea waves weaken the structure of coastal rocks, causing cracks and collapses.

A sea arch is a natural bridge-like formation formed when waves erode entirely through a headland or sea cave.

The roots of trees bind the soil particles firmly together and foliage protects against rain impact, effectively preventing soil erosion.