The role of water in the development of surface roughness and mineralogical variability on playa surface sediments: implications for aeolian erodibility and dust emission

Open Access
Author:
Tollerud, Heather Joy
Graduate Program:
Geosciences
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 03, 2014
Committee Members:
  • Matthew Scott Fantle, Dissertation Advisor
  • Susan Louise Brantley, Committee Member
  • James Kasting, Committee Member
  • Timothy Joseph Kane, Special Member
Keywords:
  • Aeolian erodibility
  • Atm. dust emission
  • Synthetic aperture radar
  • Remote sensing
  • Surface roughness
  • Black Rock Desert playa
Abstract:
Playas are significant sources for atmospheric mineral dust, but the evolution of their surface erodibility through time is not well established, leading to difficulties in modeling dust emission. Investigation of the spatial and temporal variability of surfaces within dust source regions has the potential to elucidate the processes that control erodibility and to improve model predictions of dust emission. In this dissertation the variability in time and space of surface mineralogical composition, particle size distribution, and surface roughness is measured in a playa (the Black Rock Desert, NV, USA). Water is found to be critical to the development of playa surfaces. Analysis of samples from the Black Rock playa demonstrates that the playa is mainly composed of quartz (~30 wt%), clay (~45 wt%), plagioclase (~10 wt%), calcite (2-15 wt%), and halite (0-40 wt%). Composition varies between the center of the playa (more frequently inundated) and edge, with smaller particles, more clay, less plagioclase, and less calcite in the central areas. The surface roughness of the Black Rock playa is observed through time (2004-2010) using synthetic aperture radar (SAR) remote sensing data. Surface roughness is relatively constant during the dry summer months, but changes significantly from year to year, suggesting that water and inundation have more control on playa surfaces than anthropogenic activity or saltation abrasion. Roughness is low in years with heavy precipitation, but late drying areas of the playa are rough. Small scale lab experiments on a playa analog surface demonstrate that cycles of wetting/drying increase roughness, particularly for surfaces with added CaCO3; a surface with added CaCO3 produced aggregates of a size appropriate for saltation (< 100 microns) through wetting/drying cycles, while a surface with added NaCl remained relatively smooth. These observations suggest a conceptual framework for the development of surfaces in a playa: inundation smooths the playa surface while cycles of wetting/drying roughen it. The surface is particularly susceptible to roughening when it is rich in calcite.