Back wasting, also known as back wearing, is a fundamental geomorphological process characterized by the recession or retreat of a slope face with little to no significant loss of its original steepness. Essentially, the slope moves backward across the landscape while maintaining its angle.
This process plays a crucial role in shaping landforms, particularly in environments where weathering and erosion rates support this specific type of slope evolution.
Understanding the Process
Back wasting describes how slopes erode laterally rather than primarily flattening out. Instead of becoming gentler, the slope face itself migrates away from its original position.
Here's a breakdown of its key characteristics and implications:
- Slope Recession: The primary feature is the backward movement of the slope.
- Constant Steepness: Crucially, the angle of the slope remains largely unchanged as it recedes.
- Lateral Valley Widening: In the context of valleys, back wasting leads to their lateral widening. As the valley sides retreat, the valley floor expands.
- Narrowing of Water Divides: A direct consequence of valleys widening through back wasting is the narrowing of the ridges or divides separating adjacent drainage basins. Over time, these divides can become sharper and more pronounced or eventually be entirely consumed.
Environmental Dominance
Back wasting is particularly recognized as a potentially dominant process in certain tropical environments. The specific climatic and weathering conditions in these regions—such as high rainfall, deep chemical weathering, and dense vegetation—can favor the steady retreat of slopes while preserving their angle.
Historical Context
The concept of back wearing was notably envisaged by William Morris Davis (W.M. Davis) in his influential cycle of erosion. Davis's model, which describes the evolution of landscapes through stages of youth, maturity, and old age, incorporated the idea of slopes retreating parallel to themselves as a key mechanism in landscape development.
Key Characteristics of Back Wasting
| Characteristic | Description | Impact on Landscape |
|---|---|---|
| Slope Recession | Slopes move backward or away from their initial position. | Creates expanding valleys and migrating landforms. |
| Steepness Retention | The angle of the slope face remains largely constant during recession. | Maintains characteristic relief and prevents rapid flattening of terrain. |
| Lateral Valley Widening | Valleys expand sideways as their confining slopes retreat. | Leads to broader valley floors over geological timescales. |
| Water Divide Narrowing | Ridges between adjacent valleys become thinner due to valley expansion. | Can result in sharper, more incised divides or eventual planation of interfluves. |
Practical Insights
Understanding back wasting is vital for:
- Geomorphological Research: It helps scientists model and predict how landscapes evolve over long periods, especially in tropical and tectonically stable regions.
- Environmental Planning: Knowledge of slope recession rates can inform land-use planning, particularly in areas susceptible to this process, by understanding how landforms might change.
- Engineering Geology: In some cases, recognizing the potential for back wasting is important for infrastructure development near slopes, as it implies a stable but retreating slope rather than one prone to catastrophic failure.
In summary, back wasting represents a fundamental way landscapes change, demonstrating that erosion isn't always about reducing elevation, but often involves reshaping topography through the lateral movement of its distinctive features.
