Upper Course Landforms (Interlocking Spurs)

Definition and Formation

Interlocking spurs are a series of ridges that extend alternately from the valley sides into the river valley. They are formed in the upper course of a river where the river flows through hard, resistant rock. Because the river has limited energy to erode sideways, it winds around these ridges, cutting down vertically instead. This creates a narrow, steep-sided valley with the spurs appearing to "interlock" like the teeth of a zip on either side of the river.

The river cannot cut through the hard rock of the spurs, so it bends around them, creating a winding valley shape. This process happens mainly in the upper course where the river’s gradient is steep and vertical erosion dominates.

Processes Involved

In the upper course, vertical erosion is the dominant process shaping the landscape. The river has a steep gradient and a lot of potential energy, so it cuts downwards into the valley bed through processes like hydraulic action and abrasion. This deepens the valley but does not widen it much because lateral erosion is limited.

The path of the river is influenced by the presence of resistant rock. The river flows around these areas of hard rock rather than eroding through them, leading to the formation of interlocking spurs. The river’s energy is focused on downward erosion rather than sideways, so the valley remains narrow and V-shaped.

Characteristics

• Steep-sided valleys with a narrow floor
• Alternating ridges (spurs) projecting from each side of the valley
• V-shaped valley cross-section due to vertical erosion
• River winds around the spurs, creating a zigzag pattern
• Visible on the river’s long profile as a steep gradient section

These features are typical of upland river valleys where the river is actively eroding downwards but has little energy to erode sideways.

Examples in the UK

Interlocking spurs are common in the upper courses of many UK rivers, especially in upland areas such as the Pennines and the Lake District. Examples include:

• River Tees: In its upper course, the River Tees flows through a steep, narrow valley with prominent interlocking spurs before reaching the famous High Force waterfall.
• River Wye: The upper reaches of the River Wye in the Welsh borders show clear interlocking spurs as the river winds through resistant rock.
• Other upland rivers in the UK often show similar landforms where the valley is narrow and steep-sided with alternating spurs.

These interlocking spurs support diverse upland ecosystems, providing habitats for plants and animals adapted to steep, rocky environments.

Learning Example

For instance, imagine a river flowing through a steep valley where the river encounters a ridge of hard rock on its right side. Because the river cannot erode through this hard rock, it bends to the left, cutting down vertically into softer rock. On the left side, another ridge of hard rock forces the river back to the right. This alternating pattern of ridges creates interlocking spurs.