In popular concept, a desert should be hot, barren, and, preferably, sandy. In reality, many deserts are few, or none of these things. Most deserts are, however, areas of aridity, and it is upon this property that the scientific definition of deserts has generally hinged. Even so, providing an acceptable measure of aridity upon which to base a definition of desert areas has not been straightforward, and several attempts based upon a variety of geomorphic, climatic, and/or vegetational indices of aridity have been made to identify the world distribution of deserts.

Climatic Accidents in Landscape Making.

Geomorphology of Desert Environments

ological finds in the arid and semiarid western United States is based on geology, on the relationship between moisture, vegetation, and geological processes, and on climatic history. The procedure of dating includes 4 main steps, namely, (1) study of beds and geological features, (2) climatic interpretation of beds and features, (3) assignment of the bed with the human record to a particular regional climatic age or phase, and (4) correlation of the regional relative chronology with a dated climatic history. The geological study of the site includes texture, structure, and appearance of the beds or terrace deposits, their modes and conditions of formation, their sequence, fossils, and artifacts, the soil zones, caliche incrustations, and erosions. The climatic interpretation of the beds and features is made in conformity with the delicate regional relationship between climatic conditions and changes and geological processes and deposits. The regional correlation is carried out with consideration of the areal extent of the moisture conditions and of the

Geologic-Climatic Dating in the West

Davis, in his early writings (1899–1909) recognised, by implication, that some aspects of the geographic cycle were related to the climatic regime under which they were formed. This was a corollary to his classic formula: form is the result of the influence of structure plus process plus stage. Davis, in recognising the existence of the arid and glacial cycles, which he called climatic accidents, also recognised that process was dependent on climate.

https://www.jstor.org/stable/pdfplus/2561059.pdf

The Geographic Cycle in Periglacial Regions as it is Related to Climatic Geomorphology

The depth to unweathered bedrock beneath landscapes influences subsurface runoff paths, erosional processes, moisture availability to biota, and water flux to the atmosphere. Here we propose a quantitative model to predict the vertical extent of weathered rock underlying soil-mantled hillslopes. We hypothesize that once fresh bedrock, saturated with nearly stagnant fluid, is advected into the near surface through uplift and erosion, channel incision produces a lateral head gradient within the fresh bedrock inducing drainage toward the channel. Drainage of the fresh bedrock causes weathering through drying and permits the introduction of atmospheric and biotically controlled acids and oxidants such that the boundary between weathered and unweathered bedrock is set by the uppermost elevation of undrained fresh bedrock, Zb. The slow drainage of fresh bedrock exerts a “bottom up” control on the advance of the weathering front. The thickness of the weathered zone is calculated as the difference between the predicted topographic surface profile (driven by erosion) and the predicted groundwater profile (driven by drainage of fresh bedrock). For the steady-state, soil-mantled case, a coupled analytical solution arises in which both profiles are driven by channel incision. The model predicts a thickening of the weathered zone upslope and, consequently, a progressive upslope increase in the residence time of bedrock in the weathered zone. Two nondimensional numbers corresponding to the mean hillslope gradient and mean groundwater-table gradient emerge and their ratio defines the proportion of the hillslope relief that is unweathered. Field data from three field sites are consistent with model predictions.

https://www.pnas.org/content/pnas/111/18/6576.full.pdf

Climatic Accidents in Landscape Making.

Citations

Geomorphology of Desert Environments

Geologic-Climatic Dating in the West

The Geographic Cycle in Periglacial Regions as it is Related to Climatic Geomorphology

Geomorphology of Desert Environments

A bottom-up control on fresh-bedrock topography under landscapes

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