1. Frost Wedging: When water seeps into cracks and pores of rocks and subsequently freezes, it expands in volume, exerting tremendous pressure. This repeated freezing and thawing action can cause the rock to break into fragments with sharp and angular edges due to the expansion and contraction stresses.
2. Thermal Stress Fracturing: Extreme temperature variations can induce thermal stresses within rocks. During hot days, rocks expand, and during cold nights, they contract. Over time, this repeated expansion and contraction can cause fracturing and breakage, resulting in uneven angular pieces of rock.
3. Abrasion and Erosion: When rocks are exposed to abrasion from wind, water, or other materials, their surfaces undergo gradual erosion. This abrasive action can produce uneven angular shapes as the softer regions of the rock erode faster than the more resistant portions.
4. Exfoliation: Some rocks, especially those formed through volcanic processes, contain concentric layers or bands. Weathering can weaken the bonds between these layers causing them to peel off, exposing fresh and uneven surfaces with angular edges.
5. Pressure Release: Deep underground, rocks are subjected to intense confining pressure. When these rocks are brought to the surface due to tectonic uplift or glacial retreat, the sudden pressure release causes them to expand and break into blocks, often with irregular and angular shapes.
In summary, uneven angular rocks form primarily due to mechanical weathering processes such as frost wedging, thermal stress fracturing, abrasion, exfoliation, and pressure release. These processes create fractured surfaces with sharp and angular edges, leading to the characteristic uneven shapes often observed in rocky terrains.