Figure 2—Cartoon of tor development

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Figure 2—Cartoon of tor development.
Panel A: Tor and inselberg formation under the 2-stage etching hypothesis. Areas of lower joint density, and hence more structurally competent rock, weather more slowly than areas of higher joint density. Stripping of the weathering mantle exposes a mass of tor-forming boulders.
Panel B: Tor formation through regolith thickness instability, as described in the vignette. ‘Regolith’ refers to loose weathered debris resting on the bedrock (i.e., the sediment blanket). Initially, the sediment blanket has a stable thickness of heq’. Focused erosion causes thinning of the sediment blanket to the point at which it is unstable. As thinning continues at this discrete location, bedrock weathers more slowly than adjoining bedrock covered by a thicker sediment blanket. This process eventually leads to tor growth and exposure at the surface, without invoking any particularities of bedrock structure.

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Mark Strudley
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