Geography · Ch 11 — Geomorphic Processes
Special Effects of Weathering
Special Effects of Weathering
The photograph shows a single rock outcrop, its surface stripped bare of soil or vegetation. The most striking feature is the way the rock has come apart in a series of curved, shell-like layers, each one peeling away from the one beneath it. These layers are not flat or jagged; they follow the rounded contour of the boulder, giving the whole surface a smooth, onion-like appearance. The outer sheets are visibly loosened and detached, some still clinging to the rock while others have already fallen away, leaving behind a fresh, rounded surface underneath.
What the image captures is the end result of exfoliation, not the process itself. The curved shells are the "flakes" that have split off from the parent rock, and the smooth, rounded form of the outcrop is precisely what this peeling produces. The caption pairs this with "granular disintegration," but the photograph itself focuses on the flaking — the separation of large, curved sheets rather than individual grains. The rounded shape is the key visual clue: it tells you that the rock has been shaped by the removal of successive layers, each one following the curve of the surface it once covered. …
Exfoliation is not a separate weathering process at all — it is a result. The actual processes that cause it are the physical weathering mechanisms you have already met: unloading, thermal contraction and expansion, and salt weathering. What makes exfoliation worth studying on its own is the distinctive form it produces on the landscape.
When these processes act on exposed bedrock, they cause the outer layers to peel or flake off in curved sheets, somewhat like the layers of an onion. This flaking of more or less curved sheets from the surface of rocks or bedrock leaves behind smooth and rounded surfaces. The repeated peeling gradually wears away sharp edges and angular outlines, giving the rock a characteristic domed or rounded appearance.
Two specific landforms arise from this effect, and each is tied to a different underlying cause:
- Exfoliation domes — these result from unloading. When overlying rock is removed by erosion, the pressure on the rock below is released, and the outer layers expand and crack parallel to the surface, peeling off in curved sheets to form a smooth dome.
- Tors — these result from thermal expansion. Repeated heating and cooling of the rock causes the surface layers to expand and contract at a different rate from the interior, eventually causing them to peel away and leave behind isolated, blocky rock masses. …