The formation and characteristics of interlocking spurs

In the upper stage of a river, the primary process of erosion is vertical, meaning the river cuts downwards into the landscape rather than widening sideways. This vertical erosion, combined with the river's path through varied terrain, leads to the creation of distinct landforms known as interlocking spurs.

How interlocking spurs are formed

• Vertical erosion - The river erodes downwards, deepening its channel as it flows through the upper stage.
• Twisting pathway - As the river encounters obstacles of hard rock, it winds and turns to navigate around them, creating pronounced ridges.
• Interlocking ridges - These ridges, or spurs, protrude from alternating sides of the river valley and interlock with each other, resembling the teeth of a zip fastener.
• V-shaped valley association - Interlocking spurs are typically found within V-shaped valleys, which are narrow and steep-sided due to the dominant downward erosion.

The process of waterfall formation and associated features

Waterfalls are striking features often found in the upper stage of a river, where the riverbed has significant variations in rock resistance. They form at steep sections where the river's erosive power interacts with layers of differing rock types, leading to dramatic changes in the landscape.

Stages of waterfall formation

• Differential erosion - When a river flows over a band of hard rock followed by softer rock downstream, the softer rock erodes much faster, creating a steep drop or waterfall.
• Plunge pool creation - At the base of the waterfall, the force of the falling water erodes the softer rock further, forming a deep depression known as a plunge pool.
• Undercutting and retreat - The water undercuts the hard rock layer above by eroding the softer rock beneath it, causing the overhang to collapse over time. This process makes the waterfall retreat upstream.
• Gorge development - As the waterfall moves upstream due to undercutting and collapse, it leaves behind a narrow, steep-sided channel called a gorge.

The development of rapids in the upper stage of a river

Rapids are another characteristic feature of the upper stage of a river, often occurring where the riverbed is uneven due to alternating bands of rock with different levels of resistance. These create turbulent sections of water flow, distinct from the dramatic single drop of a waterfall.

How rapids are formed

Rapids develop where a river flows over alternating layers of hard and soft rock. The softer rock erodes more rapidly than the harder rock, resulting in an irregular riverbed with small, stepped drops. The uneven bed causes the water to become agitated and turbulent, forming a series of mini-waterfalls or rapids as the river navigates these variations.

Characteristics of rapids

• Series of small drops - Unlike a single large waterfall, rapids consist of multiple smaller drops along the river's course.
• Turbulent water surface - The water appears rough and choppy due to the disruption caused by the uneven riverbed.
• Location in upper stage - Rapids are typically found in the upper reaches of a river where vertical erosion dominates and rock resistance varies significantly.