Geology topics

Dale A. Gillette

Publications and source records attributed to Dale A. Gillette.

3 recordsLinked to original sources

USGS2001

Supply-limited horizontal sand drift at an ephemerally crusted, unvegetated saline playa

A site at Owens Dry Lake was observed for more than 4 years. The site was a vegetation-free saline playa where the surface formed “ephemeral crusts,” crusts that form after rainfall. Sometimes these crusts were destroyed and often a layer of particles on the crust would engage in vigorous aeolian activity. Three “phases” of active sand drifting are defined as almost no movement (extreme supply limitation), loose particles on crust with some degree of sand drift (moderate supply limitation), and unlimited source movement corresponding to a destroyed surface crust (unlimited supply). These “phases” occurred 45, 49, and 6% of the time, respectively. The accumulation of loose particles on the crust was mostly the result of in situ formation. Crusted sediments with loose particles on top can exhibit mass flux rates about the same as for noncrusted sediments. Crusted sediments limit or eliminate sand drift in two conditions: for rough crusts that effect a sufficiently high threshold friction velocity (above the wind friction velocity) and for limited amounts of loose particles on the crust where particle supply is less than would be transported in normal saltation for a thick sandy surface. These “supply-limited” cases are similar to wind erosion of limited spilled material on a hard concrete surface. We quantified “supply limitation” by defining a “potential” or “supply unlimited” sand drift function Q = AG where A represents supply limitation that decreases as the particle source is depleted. Here Q is the mass of sand transported through a surface perpendicular to the ground and to the wind and having unit width during time period t , and G = ∫ u * ( u 2 * − u 2 * t ) dt for u * > u * t . G is integrated for the same time period t as for Q , u * is the friction velocity of the wind, and u * t is the threshold friction velocity of the wind. Hard crusts (usually formed in the summer) tended to show almost no change of threshold friction velocity with time and often gave total protection from wind erosion. Rough crusts provided sufficient protection expressed as high threshold friction velocities. For these high threshold friction velocities, aeolian activity was greatly reduced or practically prevented. The softest crusts, usually formed in the winter, provided much less protection and sometimes were destroyed by the wind. Following this destruction the “potential” or “supply unlimited” sand drift would be observed.

California↗

USGS1997

Disturbance of biological soil crusts: Impacts on potential wind erodibility of sandy desert soils in southeastern Utah

Friction threshold velocities (FTVs) were determined for biological soil crusts in different stages of recovery. Particles on the surface of crusts that had been relatively undisturbed for at least 20 years were found to have significantly higher FTVs than those that had been disturbed 5, 10 or 1 years previously (376, 87, and 46 cm sec -1 , respectively). FTV's for crust breakage was also much higher for undisturbed crusts when compared to the previously disturbed crusts (573, 148, and 88 cm sec -1 , respectively). All crusted surfaces were more stable than bare sand, which had an FTV of 16 cm sec -1 . Disturbance treatments were then applied to the three crustal classes. Disturbance significantly reduced the FTVs of all classes by 73±92 per cent. Comparing crustal FTVs with mean and high monthly wind speeds found in this region, it was observed that only crusts that had been undisturbed for approximately 20 years or more were able to protect soil surfaces from wind gusts expected on the average of once a month. Other crustal classes, as well as all disturbance treatments, had FTVs lower or equal to that of commonly occurring winds in this region. Because most of the crustal biomass occurs in the top 0-3 mm of soils, even slight soil loss can negatively influence stability and nutrient inputs to this ecosystem.

Utah↗

USGS1994

The origin and evolution of dust clouds in Central Asia

Data from a high resolution radiometer AVHRR (580–680 nm optical lengthwaves) installed on the “NOAA-11” satellite as well as TV (500–700 nm) and IR (8000–12000 nm) equipment of the Russia satellite “Meteor-2/16” were used to study the evolution of dust storms for 1–30 September 1989 in Tajikistan, Uzbekistan, Turkmenistan and Afghanistan. These data help to validate the hypothesis, that long-term dusted boundary layer (duration of the order of a day or more), but of comparatively not high optical density (4–10 km meteorological visibility range at the 20–50 km background), is formed after the northwest intrusions into a region of intensive cold fronts at the surface wind velocities of 7–15 m/s. Stability of dust clouds of vertical power to 3–3.5 km (up to an inversion level) is explained by an action of collective buoyancy factors at heating the dust particles of 2–4 μm in mean diameter by solar radiation. The more intensive intrusions stimulate a formation of simultaneously dust and water clouds. The last partially reduce the solar radiation (by the calculations of the order of 30–50%) and decrease the role of buoyancy factors. Thus, initiated is the intensive but short-term dusted boundary layer at horizontal visibility of 50–200 m.

central Asia↗