Overview
This lecture covers the concept of slope in geomorphology, focusing on different types of slopes, how to identify them, and their significance in human activities.
Definition and Concept of Slope
- Slope refers to the rise or fall of the landscape at an angle from the horizontal.
- Horizontal surfaces are not slopes; only surfaces at an angle are considered slopes.
Types of Slopes
- Primary Slopes are formed by internal Earth forces like faulting and folding.
- Faulting creates slopes when rock cracks and one side subsides.
- Folding forms slopes when horizontal rock layers bend due to compression.
- Slopes by Erosion are formed when land is worn away by water, wind, or ice, creating features like gorges.
- Secondary Slopes result from further erosion and weathering of primary slopes, making them wider.
- Deposition Slopes form when weathered material is deposited, such as in sand dunes.
Classes of Slopes by Gradient
- Gentle Slopes have a gradient of 5–15° and are low-angle; contour lines are far apart on maps.
- Steep Slopes have gradients over 15° and are high-angle; contour lines are close together on maps.
- Concave Slopes are rounded inward, steep at the top, gentle at the bottom; contour lines close at the top, wider at the bottom.
- Convex Slopes are rounded outward, gentle at the top, steep at the bottom; contour lines far apart at the top, close at the bottom.
Significance of Slopes
- Settlements may be built on slopes for views or sunlight, especially on north-facing slopes in the Southern Hemisphere.
- Forestry can take place on steeper slopes as trees can survive there.
- Contour Ploughing is used in farming to minimize soil erosion by following the slope's contours.
- Recreation activities like hiking, mountaineering, and skiing occur on slopes.
- Infrastructure such as roads and railways are challenging to build on slopes and usually follow contour lines to reduce steepness and costs.
Key Terms & Definitions
- Slope — The rise or fall of the landscape at an angle from the horizontal.
- Primary Slope — Formed by Earth’s internal forces such as faulting and folding.
- Faulting — Cracking of rock, often causing one part to drop and create a slope.
- Folding — Bending of rock layers due to compression, resulting in a slope.
- Erosion — Wearing away of land by water, wind, or ice.
- Deposition — Accumulation of weathered material, forming new slopes.
- Contour Lines — Lines on a map that connect points of equal elevation, indicating slope steepness.
Action Items / Next Steps
- Review types and characteristics of slopes.
- Practice identifying different slopes using contour maps.
- Study the significance of slopes in settlement, farming, forestry, recreation, and infrastructure.