Climate–surface–pore‐water interactions on a salt crusted playa: implications for crust pattern and surface roughness development measured using terrestrial laser scanning

Abstract

Sodium accumulating playas (also termed sodic or natric playas) are typically covered by polygonal crusts with different pattern characteristics, but little is known about the short-term (hours) dynamics of these patterns or how pore water may respond to or drive changing salt crust patterning and surface roughness. It is important to understand these interactions because playa-crust surface pore-water and roughness both influence wind erosion and dust emission through controlling erodibility and erosivity. Here we present the first high resolution (10 À3 m; hours) co-located measurements of changing moisture and salt crust topography using terrestrial laser scanning (TLS) and infra-red imagery for Sua Pan, Botswana. Maximum nocturnal moisture pattern change was found on the crests of ridged surfaces during periods of low temperature and high relative humidity. These peaks experienced non-elastic expansion overnight, of up to 30 mm and up to an average of 1.5 mm/night during the 39 day measurement period. Continuous crusts however showed little nocturnal change in moisture or elevation. The dynamic nature of salt crusts and the complex feedback patterns identified emphasize how processes both above and below the surface may govern the response of playa surfaces to microclimate diurnal cycles.

The Polygonal Surface Structures in the Dalangtan Playa, Qaidam Basin, NW China: Controlling Factors for Their Formation and Implications for Analogous Martian Landforms

“…These polygons are characterized by their uplifted rims (or pressure ridges) that formed from a subsurface process of lateral salt displacement (e.g., Artieda et al, ; Christiansen, ; Lowenstein & Hardie, , and references therein) due to crystallization pressures (Handford, ) or to thermal contraction and expansion (Dellwig, ; Handford, ; Tucker, ). In fact, polygonal ridges are formed through a combination of thermodynamic and geochemical mechanisms (e.g., Lowenstein & Hardie, ; Nield et al, , and references therein). The durability of salt polygons is in most cases limited by seasonal rainfall or flooding events, which often destroy the surface morphology and then start a new cycle of the formation and evolution of salt polygons (Artieda et al, ).…”

Analyses of Recent Sediment Surface Dynamic of a Namibian Kalahari Salt Pan Based on Multitemporal Landsat and Hyperspectral Hyperion Data

“…In addition to mineralogical differences, the physical properties of the salt pan surface are altered by cattle trampling, increasing the surface roughness [107], which may also cause the reflectance to decrease even at similar salt content by casting micro shadows [108]. The rougher surface crust is also likely to be more moist [109] adding to the decrease in reflectance.…”

“…The rougher surface crust is also likely to be more moist [109] adding to the decrease in reflectance. Figure 6 shows the result of the IR-MAD analysis.…”

Correction of Incidence Angle and Distance Effects on TLS Intensity Data Based on Reference Targets

“…Apart from discrete topography measurements, almost all current TLS instruments simultaneously measure the power of the backscattered laser signal of each point and record it as an intensity value [3]. The intensity recorded by current laser scanners, either in the form of the echo amplitude or full-waveform of the backscattered laser signal [4], can be utilized as complementary information along with the point cloud in a wide range of applications, especially in visualization, segmentation [5], classification [6][7][8][9][10], and multi-temporal analysis [11][12][13][14].…”

“…The intensity value is regarded as a significant source of spectral information associated with the surface properties, e.g., reflectance [1,[15][16][17][18], roughness [15,19], moisture [11,13,14,20,21], brightness [22][23][24][25] and grain size [26,27], of the scanned object. However, the original intensity data 1.…”