Post by Professor Heather Viles, School of Geography, University of Oxford, UK.
Observations in arid and hyper-arid environments on Earth show a range of processes, often acting together or in sequence, which cause rock breakdown. These processes cut across the conventional categorisation into weathering and erosion and illustrate the synergistic associations of chemical, biological and physical weathering and aeolian abrasion. Whilst there is no exact correlation between the processes at work and the features formed, because of geomorphological equifinality and complexity, nevertheless the appearance of breakdown features is a visual signature of the processes at work.