The angle of repose is defined as the steepest angle at which a sloping surface composed of a specific loose material remains stable.

To elaborate, the angle of repose is a crucial concept in slope stability analysis. It represents the maximum angle at which a pile of unconsolidated grains can maintain stability. This angle is influenced by several factors, including the density and shape of the particles, as well as the frictional interactions between them. When a slope consisting of loose material exceeds its angle of repose, the material begins to move downhill, often resulting in a landslide.

The angle of repose can vary significantly based on the properties of the material involved. For instance, dry sand typically has an angle of repose of approximately $34^\circ$, whereas wet sand can exhibit a higher angle of repose. This increase occurs because water between the sand grains forms a temporary bond that enhances the frictional forces holding the grains together.

In the fields of geography and earth science, understanding the angle of repose is essential for predicting the stability of both natural and artificial slopes. It finds applications in numerous areas, including the design of roads and buildings in hilly terrains, as well as the assessment of landslide risk in mountainous regions.

Furthermore, the angle of repose plays a significant role in the study of hillslope morphology and evolution. The shape of a hillslope results from a balance between processes that tend to steepen the slope, such as erosion and weathering, and those that promote flattening, like the downslope movement of loose materials. The angle of repose serves as the critical threshold between these opposing processes.

In summary, the angle of repose is a fundamental concept for understanding slope formation and its evolution over time. It is a vital factor in evaluating slope stability and the potential for landslides.