Geographical Processes and Landform Development

Posted on Oct 29, 2025 in Geology

Geographical Processes: Weathering and Erosion

Key Definitions

Weathering: The rock is broken down and is weakened but does not move.

Erosion: When rock is worn away and moved by forces of nature.

Types of Weathering

Weathering can be categorized as:

  • Mechanical
  • Chemical
  • Freeze-thaw
  • Biological
  • Onion-skin (Physical)

Chemical Weathering

This occurs when acids in rain and sea/river water react with rock, causing it to wear away.

Freeze-Thaw Weathering

  1. Water fills a crack in a rock.
  2. The water freezes and expands.
  3. The rock breaks into little pieces.

Processes of Fluvial Erosion (River Action)

Rivers erode their banks and beds through several key processes:

  • Abrasion: The river uses rocks and stones to wear away the banks and beds.
  • Solution: Some rock dissolves in the water.
  • Attrition: Rocks and stones rub and knock against each other, becoming smooth and rounded.
  • Hydraulic Action: The river forces air into cracks in the bed and banks; the air expands, causing the bank to crumble.

Fluvial Landforms (River Features)

Drainage Basin

A drainage basin is the area of land around the river that is drained by the river and its tributaries.

Landforms

A landform is a shape or characteristic of the land caused by either erosional or depositional processes.

Gorge

A gorge is a sloped, narrow, steep-sided valley usually found immediately downstream of a waterfall. It is formed by the gradual retreat of waterfalls over hundreds, sometimes thousands of years.

Waterfall

Waterfalls are found in the upper course, where a layer of hard rock sits on top of a layer of soft rock. As the water hits the bottom of the waterfall, it erodes the soft rock through hydraulic action and abrasion, creating a plunge pool. Over time, the plunge pool gets bigger until the hard rock overhangs. Eventually, the hard rock will collapse, and the waterfall will retreat upstream, leaving a steep-sided gorge.

Meanders and Floodplains

Meanders are found in the middle course, usually in lowland and flatter areas. The dominant form of erosion here is lateral erosion. Due to constant erosion and deposition, meanders are always changing shape. The flat area of land on either side of the meanders is called a floodplain.

Oxbow Lakes

Oxbow lakes are found in the middle course. They form when a meander is cut off from the main channel because the meander neck is eroded away.

Oxbow Lake Formation Steps

  1. The neck of the meander is gradually eroded.
  2. Water takes the fast route across the neck.
  3. Deposition seals off the meander.
  4. The meander neck is eroded completely.
  5. The meander is cut off, forming an oxbow lake.

Coastal Landforms

Headlands and Bays: Differential Erosion

Differential erosion refers to different rates of erosion. The coast is made up of bands of different types of rock. Some rock types, such as granite, are hard rock and are resistant to erosion. Headlands and bays are created when layers of hard and soft rocks are perpendicular to the sea. When they are parallel, they erode at the same time.

Coastal Erosion Sequence

Caves

Waves erode cracks in the headland. The crack widens due to processes like hydraulic action. Erosion continues to create a cave.

Arches

The waves continue to erode the cave until eventually the caves erode right through the headland to form an arch.

Stacks

The arch erodes more due to weathering processes like biological weathering; the top of the arch becomes unsupported. It collapses into the sea, leaving a stack.

Stumps

Erosion continues to attack the stack at the bottom until it collapses. A stump is formed when the stack collapses.

Glacial Processes and Landforms

Glacier Definition

A glacier is a slow-moving mass or river of ice formed by the accumulation and compaction of snow on mountains or near the poles.

Corrie (Cirque) Formation

  1. Snow collects in a natural hollow on the side of a mountain.
  2. The hollow is deepened and widened by the corrie glacier through the process of abrasion and plucking.
  3. The over-deepening leads to an ‘armchair’ shape characteristic of a corrie and causes a ‘rock lip’ to be formed.
  4. Eventually, the glacier and ice might melt, and a lake can form in the corrie. This is called a tarn.

Erosional Glacial Landforms

Arêtes

An arête is an erosional glacial landform. They are often found between two corries and around a pyramid peak.

Pyramid Peaks

A pyramid peak is an erosional glacial landform, formed when three or more corries cut into the same mountain. This creates a steep-sided mountain with a very sharp, often point-like shape.

Glacial Movement and Processes

The ice mass (glacier) flows. As it does this, it erodes the ground below. Examples of this are plucking and abrasion. Glaciers are found in very cold regions where lots of freeze-thaw weathering occurs.

Depositional Glacial Landforms

Erratics

An erratic is a boulder that is different from the bedrock upon which it is sitting. They have been transported or deposited by a glacier. Therefore, erratics are useful indicators of the direction the glacier traveled in.

Drumlins

Drumlins are formed of till. They are elongated features that can reach a kilometer or more in length, 500 meters or so in width, and up to 50 meters in height. It is common to find several drumlins grouped together. A collection of drumlins is called a swarm.

Moraine

Moraine is a type of landform created when a glacier deposits the material (till) that it has been transporting. It does this by melting or dragging along and dropping rocks at the side of the glacier. It is made up of unsorted angular rocks.

Types of Moraine
  • Lateral
  • Medial
  • Ground
  • Recessional
  • Terminal