R&W Exam Questions

Define subduction.

One tectonic plate moves under another and melts in the subduction zone.

Define conservative plate boundary.

Plates slide past each other, either in same or opposite directions.

How are fold mountains formed?

• Plates converge → compression → buckling

• Uplift of sediments forms mountain folds

Explain the role of water in the surface movement of sediment on slopes.

Water affects sediment movement through several processes.

Firstly, rainsplash erosion occurs when raindrops strike bare soil, dislodging particles. If the slope is angled, these particles are thrown downslope, which leads to gradual downslope movement.

Secondly, when infiltration capacity is exceeded, sheetwash occurs — this is the movement of water as a thin layer over the surface, which can transport loose sediment.

On uneven surfaces, this may form rills, concentrating the water and increasing erosion power, which results in further downslope transport of sediment.
Additionally, soil heave caused by wetting and drying or freeze-thaw cycles can gradually move particles downslope as they expand and contract.

Therefore, water acts both as a direct agent of movement and as a trigger for erosion processes, particularly on slopes with limited vegetation.

Name and explain two factors that influence the rate of weathering.

1. Temperature

   • Freeze-thaw cycles increase with frequent temperature changes

   • Higher temperatures speed up chemical weathering (Van’t Hoff’s Law)

2. Rock type & structure

   • Some minerals weather faster

   • Rocks with joints and bedding planes weather more quickly

Explain how afforestation can reduce mass movement on a slope.

Afforestation can reduce mass movement primarily through the role of vegetation in increasing slope stability. Firstly, tree roots bind soil particles together, which enhances the soil's shear strength. As a result, the resistance to downward movement due to gravity is increased.

Furthermore, the canopy of trees intercepts rainfall, and water is also taken up by roots and lost through transpiration. Consequently, there is a reduction in soil moisture content, which lowers pore water pressure and thus decreases the likelihood of slope failure.

In addition, less moisture means a reduction in the overall weight of the slope, which further minimises gravitational stress acting on it. Therefore, afforestation contributes to both mechanical and hydrological stability, especially on slopes vulnerable to shallow landslides or slumping.

Define the term rainsplash

Rainsplash is when precipitation hits bare soil, dislodging soil particles.

Define the term Rills

Rills are small, shallow channels cut by water flowing over soils.

Explain how the type and rate of weathering is influenced by precipitation.

Precipitation directly affects both the type and rate of weathering because many weathering processes rely on water as a key agent. In climates with high precipitation, chemical weathering dominates. This is because water facilitates reactions like hydrolysis, carbonation, and oxidation, which break down minerals in rock over time.

For example, in humid tropical climates, high rainfall leads to intense leaching, enhancing the rate of decomposition of rocks. In contrast, arid regions with low precipitation experience limited chemical weathering, as insufficient water restricts these reactions.

However, precipitation also affects physical weathering. In climates with fluctuating temperatures and moderate rainfall, freeze-thaw cycles become significant. Water enters cracks in rocks, freezes, expands, and exerts pressure on the rock, leading to its breakdown.

Thus, the availability of water determines not only how fast weathering occurs but also which weathering processes are most active. The greater the water input, the more effective both chemical and physical weathering processes tend to be, though the specific outcomes also depend on temperature.

Briefly explain how afforestation can reduce mass movement on a slope.

• Trees intercept and absorb water, reducing soil moisture and lowering pore water pressure.

• Roots bind soil material, increasing shear strength and reducing the likelihood of mass movement.

• It also decreases the overall water content and weight of the slope, though tree weight may slightly counteract this.

Explain how the type and rate of weathering is influenced by precipitation.

Precipitation significantly affects both the type and rate of weathering, because many weathering processes are water-dependent. In areas with high rainfall, such as the Amazon Basin, chemical weathering dominates. This includes processes like hydrolysis, carbonation, and chelation, which rely on water to react with minerals in rocks. As a result, the rate of chemical breakdown is high due to the continuous presence of moisture.

In contrast, in arid regions like the Sahara Desert, precipitation is limited, so chemical weathering is much slower or even absent. Instead, physical weathering such as salt crystallisation becomes more dominant, although its effectiveness is also reduced due to lack of moisture.

Furthermore, in mid-latitude regions with seasonal precipitation and fluctuating temperatures, freeze–thaw weathering is common. Here, water enters rock cracks, freezes, and expands, exerting pressure on the rock. This repetitive action increases the rate of physical breakdown.

Therefore, both the availability and variability of precipitation directly control which weathering processes are active and how rapidly they occur. More water generally leads to more intense and diverse weathering, while limited water restricts both type and effectiveness.

Define the weathering terms heating/cooling and hydration.

Heating/cooling: Daily temperature changes cause expansion (day) and contraction (night) of rock, leading to breakdown from stress.

Hydration: Minerals absorb water, swell, and exert pressure on the rock, causing physical breakdown.

Briefly explain how rockfalls occur on slopes.

Rockfalls occur due to freeze–thaw weathering in joints, seismic activity, slope undercutting, or human activity like overloading. Steep slopes and gravity increase the risk.

Describe and explain the formation of volcanic island arcs.

Volcanic island arcs form at convergent boundaries where one oceanic plate subducts beneath another.

As the denser plate sinks into the mantle, it melts due to friction and pressure, producing magma. This magma is less dense, so it rises through the overlying plate and erupts, forming volcanic islands.

Over time, a chain of volcanoes develops along the subduction zone, often curved due to the Earth's spherical shape and plate movement.

Examples include the Mariana Islands and the Aleutian Islands.

This process involves deep ocean trenches, intense seismic activity, and andesitic magma, characteristic of explosive eruptions.