Weathering: physical, chemical, and biological

Thermal change or pressure release can peel outer layers. In exams onion like layers indicate exfoliation.

Organic acids from organisms can chemically alter minerals. In exams do not limit biological weathering to roots only.

In physical weathering size changes but mineral composition mostly remains the same. For exams remember composition versus size.

Forest adds organic acids and root action while rainfall increases chemical reactions. In exams study rainfall and organisms together.

Different minerals respond differently to heat causing grains to separate. For exams treat multi mineral rocks as the clue.

Quartz is generally more stable and resistant under common conditions. In exams connect quartz with sandy residues.

Calcite can dissolve easily in mildly acidic water. For exams link calcite and limestone with carbonation.

Removal exposes fresh rock surfaces so weathering can continue. In exams connect slopes with removal of material.

Direct answer: Option C, a long-stable surface with sufficient moisture. Weathering depth means how far weathering has progressed below the ground surface. Chemical weathering needs water, and it also needs time to act. On a stable surface, soil and rock remain in place for a long period instead of being quickly removed. Moisture can then enter cracks and pores repeatedly, carrying chemical reactions deeper. Option C is correct because it supplies both important factors: long duration and adequate water. Option A is wrong because very little rainfall provides little water, while rapid removal prevents a deep weathered layer from developing. Option B is wrong because continuous ice cover and no water flow greatly restrict the movement of liquid water and chemical reactions. Option D is wrong because fresh lava is continuously added, so an old stable weathering profile cannot develop easily. Memory cue: deep weathering needs time, stability and moisture.

Low moisture reduces chemical reactions and temperature range increases physical stress. For exams remember desert conditions.

Weathering weakens and loosens material on slopes. In exams view weathering as preparation for mass movement.

Water acts as both a solvent and a medium for chemical reactions in weathering. When water is scarce, processes such as hydration, hydrolysis and solution become very slow, so thick chemically weathered soil develops less readily. Mechanical weathering may break rocks through thermal expansion or salt crystallisation, but it does not itself cause chemical alteration. Exam tip: associate arid climates mainly with mechanical weathering and limited chemical weathering.

Thick roots can widen cracks and break rocks. In exams consider root pressure a mechanical biological effect.

Feldspar hydrolysis can produce clay like minerals. In exams remember feldspar forming kaolin like products.

Joints and faults provide pathways for water and air to depth. In exams treat structural weakness as a weathering route.

Physical weathering reduces size but usually does not alter composition. For exams remember it as mechanical breakdown.

Breakage increases surface area and then water speeds chemical alteration. For exams see processes as connected as well as separate.

Weathering results from many factors not hardness alone. In exams remember structure minerals and climate together.

High moisture and heat drive mineral alteration to depth. For exams link deep weathering mantle with humid tropical climate.

With few cracks entry of water and air is limited. In exams connect lack of structural weakness with slow weathering.

Roots exert pressure and microorganisms may release acids. In exams remember both forms of biological weathering.

In solution water can dissolve and carry soluble substances. For exams this is the most direct chemical process.

Weathering prepares rock for erosion by breaking and altering it. In exams treat it as preparation for landform formation.

Heavy rainfall removes soluble materials by leaching and leaves iron aluminium residues. In exams link laterite with humid tropical weathering.

Deep weathering along joints leaves corestones and tors appear after loose material is removed. For exams remember tors with granite and joint controlled weathering.