Earth’s External Processes and Landform Development Weathering, erosion, transportation and deposition; resulting landforms (valleys, deltas, beaches, dunes, floodplains).

GEOGRAPHY: Earth's External Processes and Landform Development (SS2)

Welcome, SS2 students! Today, we will explore how Earth's surface is constantly being shaped by external forces. These forces work together to break down rocks, move the broken materials, and then deposit them elsewhere, creating diverse landforms we see around us.

Core Concepts

Earth's external processes involve a series of actions: weathering, erosion, transportation, and deposition.

1. Weathering

Weathering is the process where rocks are broken down into smaller pieces or dissolved in situ (on the spot) without much movement. There are three main types:

• Physical Weathering: Rocks break into smaller fragments due to forces like temperature changes (expansion and contraction), freezing and thawing of water in cracks (frost shattering), or the growth of salt crystals.
• Chemical Weathering: Rocks are changed into new substances through chemical reactions, such as rusting (oxidation), dissolution by rainwater (carbonation), or reaction with acids from decaying plants.
• Biological Weathering: Living organisms, like plant roots growing into rock cracks or animals burrowing, break down rocks.

This image shows exfoliation, a type of physical weathering where layers of rock peel away due to pressure release.

2. Erosion

Erosion is the process by which weathered rock material (sediment) is picked up and carried away from its original location. It always involves movement. The main agents of erosion are:

• Water: Rivers, rain, and ocean waves.
• Wind: Especially in dry areas.
• Ice: Glaciers (though less relevant in Nigeria).
• Gravity: Mass wasting like landslides.

3. Transportation

Transportation is the movement of eroded material from one place to another. The agents of erosion also act as agents of transportation. For example:

• Rivers transport sediments through rolling, bouncing, suspension (fine particles floating), and solution (dissolved minerals).
• Wind transports sand grains by bouncing (saltation) and finer dust by suspension.
• Waves transport sand along coastlines.

4. Deposition

Deposition is the process where transported sediments are dropped or laid down when the agent of transportation (water, wind, ice) loses energy. Heavier and larger particles are usually deposited first. Deposition leads to the formation of new landforms.

Resulting Landforms

These processes collectively create many common landforms:

• Valleys: Formed mainly by river erosion. Rivers cut downward, creating V-shaped valleys in their upper courses and wider, U-shaped valleys in their lower courses as they erode sideways. This image shows a typical V-shaped valley, carved by a river.

• Deltas: Triangular-shaped landforms created at the mouth of a river where it meets a larger body of water (like an ocean or lake). The river's speed slows down significantly, causing it to deposit large amounts of sediment. An aerial view of the Niger Delta, a massive landform created by the deposition of sediments from the Niger River.

• Beaches: Accumulations of sand, gravel, or pebbles along coastlines, formed by the depositional action of waves and currents.

• Dunes: Mounds or ridges of sand formed by the wind. They are common in deserts and coastal areas where sand is abundant and wind is strong enough to transport it. This image displays sand dunes, sculpted by wind deposition.

• Floodplains: Flat, low-lying areas adjacent to a river, formed by the deposition of fine sediments during periods of flooding. When a river overflows its banks, the water spreads out, slows down, and deposits silt and clay, enriching the soil.

Real-World Example

The Niger Delta in Nigeria is a prime example of a massive landform shaped by external processes. The Niger River carries vast amounts of sediment from its long journey across West Africa. As it approaches the Atlantic Ocean, its speed decreases, and it deposits these sediments, forming the extensive delta. This process has created a fertile, low-lying region crisscrossed by numerous distributaries, rich in biodiversity and natural resources.

Practice/Reflection Question

Think about your local environment. Can you identify any signs of weathering, erosion, or deposition (e.g., potholes in roads, gullies after heavy rain, sandbanks in a nearby stream)? How might human activities affect these natural processes?