Question

Name the deposit that forms when a mountain river runs onto a plain. A) subsidence C) infiltration B) an alluvial fan D) water diversion

Short answer

B) an alluvial fan

Step-by-step solution

Define Key Terms

Identify and define the key terms presented in the exercise: 'subsidence', 'infiltration', 'alluvial fan', and 'water diversion'. 'Subsidence' refers to the gradual caving in or sinking of an area of land. 'Infiltration' is the process by which water on the ground surface enters the soil. An 'alluvial fan' is a triangle-shaped deposit of gravel, sand, and other debris that forms when a fast-flowing river or stream flattens, slows, and spreads typically at the exit onto a plain. 'Water diversion' involves rerouting water from its natural path.

Analyze the River and Landscape Dynamics

Consider the geological dynamics of a mountain river transitioning onto a plain. As the river descends from a mountain, it typically carries sediments and, upon meeting the flatter terrain of a plain, the water's speed decreases, causing these sediments to spread out, forming specific geological structures.

Identify the Correct Deposit Formation

Using the definitions and dynamics discussed, identify which of the listed options corresponds to the deposit formed by a mountain river spilling onto a plain. This geological feature, consisting of sand and sediment spread out in a fan shape, is known as an 'alluvial fan'.

Key concepts

Subsidence

Subsidence is a process where the ground effectively sinks lower relative to its surrounding area. This can happen due to various reasons like the extraction of underground resources, such as water, oil, or minerals. When these materials are removed, the ground loses support and sinks.

Some common factors that cause subsidence include:

• Natural causes like tectonic activities or the compaction of soil layers.
• Human activities such as mining operations or excessive groundwater pumping.

Subsidence can lead to severe environmental and structural issues. For example, buildings or roads on the affected area might crack or collapse due to the ground shifting underneath. It's crucial to monitor and manage activities that may lead to subsidence to prevent such damage.

Infiltration

Infiltration is a fundamental process in the hydrological cycle. It refers to water permeating into the soil from the ground surface. This process is essential for replenishing groundwater supplies and sustaining plant life.

Key factors influencing infiltration include:

• Soil composition - Sandy soils allow quicker infiltration compared to clay-heavy soils.
• Vegetation cover - Areas with dense plant life tend to have higher infiltration rates as roots create pathways for water absorption.
• Soil moisture levels - Dry soils typically absorb water more effectively than already saturated ones.

Ensuring good infiltration is crucial for water management, especially in agriculture. It helps to minimize runoff and reduces the risk of erosion.

Water Diversion

Water diversion involves altering the natural course of a waterway. This can mean channeling water away from its original path through man-made structures like dams, canals, or aqueducts.

Water diversion is undertaken for several purposes:

• Irrigation - Redirecting water to arid areas for agricultural use.
• Flood control - Reducing flow into vulnerable areas to prevent flooding.
• Urban water supply - Providing water for cities that do not have adequate natural sources.

While water diversion can offer many benefits, it also needs to be managed carefully. It can disrupt natural ecosystems, impact wildlife, and even contribute to conflict over water rights.