Desert Pavement Formation Research Articles

Soil erosion facilitates shrub encroachment in Patagonian herbaceous steppes

AbstractPrevious studies in northeastern Patagonia suggested that, mainly as a consequence of overgrazing by sheep, the herbaceous steppes are being replaced by shrub steppes dominated by Chuquiraga avellanedae as a consequence of shrub encroachment. The herbaceous steppe presents a thick sandy loam to loamy sand A‐horizon lying on a clay‐horizon while the shrub steppe presents the clay‐horizon at or near the soil surface. The thickness reduction of the remaining A‐horizon and the formation of desert pavements are evidence of soil erosion. As previous studies suggested that shrub encroachment co‐occurs with the erosion of the sandy A‐horizon, we hypothesized that shrub encroachment is favored by the presence of an clay‐horizon near the soil surface. We expected that C. avellanedae emergence and establishment would be higher as the clay horizon is closer to the soil surface and the A‐horizon is reduced. We performed field and greenhouse experiments to evaluate seedling emergence and establishment along a gradient of A‐horizon thickness. We found that the presence of a relatively thin sandy layer on the surface had a negative influence on both shrub emergence and establishment. The summer drought was not a critical period for the seedlings. Conversely, the highest seedling mortality took place during late winter in sandy soils, suggesting that these soils are more susceptible to frost heaving than clay soils. In conclusion, soil erosion in the northeastern Patagonian steppes would indirectly facilitate shrub encroachment due to differences in frost heaving susceptibility between sandy and clay soils.

Processes of Paleoindian site and desert pavement formation in the Atacama Desert, Chile

AbstractA distinct feature of many of the earliest archaeological sites (13,000-11,200 cal yr BP) at the core of the Atacama Desert is that they lie at or just below the surface, often encased in desert pavements. In this study, we compare these sites and undisturbed desert pavements to understand archaeological site formation and pavement development and recovery. Our results indicate these pavements and their soils are poorly developed regardless of their age. We propose that this is because of sustained lack of rain and extreme physical breakdown of clasts by salt expansion. Thus, the core of the Atacama provides an example of the lower limits of rainfall (<50 mm/yr) needed to form desert pavements. At site Quebrada Maní 12 (QM12), humans destroyed the pavement. After abandonment, human-made depressions were filled with eolian sands, incorporating artifacts in shallow deposits. Small and medium-sized artifacts preferentially migrated upwards, perhaps due to earthquakes and the action of salts. These artifacts, which now form palimpsests at the surface, helped – along with older clasts - to restore surface clast cover. Larger archaeological features remained undisturbed on top of a deeper Byzm horizon. The vesicular A horizons (Av horizons) have not regenerated on the archaeological sites due to extreme scarcity of rainfall during the Holocene.

Formation of desert pavements and the interpretation of lithic-strewn landscapes of the central Sahara

This study focuses on two different but interlinked lines of evidence that critically examine land surface processes contributing to the formation of desert pavements in the central Sahara. (1) Soil pedostratigraphies from the Messak plateau (SW Libya) illustrate phases of land surface stability and instability that reflect humid and arid phases of Quaternary climate, respectively. (2) The density and morphologies of surface lithic scatters in the same region were re-examined, based on data previously published by Foley and Lahr (2015, PLoS ONE). This re-examination shows that many surface clasts previously interpreted as lithics are better interpreted as formed by in situ weathering and wind abrasion. Furthermore, weathering, abrasion and deflation are the major processes by which desert clasts are formed and concentrated on the land surface, not human agency. Erosional Quaternary periods allowed for the formation of condensed pedostratigraphies by which surface clasts and lithics were mixed and concentrated on the land surface. These two independent lines of evidence show that desert land surfaces do not reflect a single time period of formation, and that Quaternary desert pavements (including any lithics located thereon) evolved in response to subaerial weathering and erosion processes.

고등학교 세계지리 교과서의 사막포도 형성에 대한 고찰

고등학교 세계지리 교과서의 사막포도 형성에 대한 고찰

Distribution of soil taxa in Antarctica: A preliminary analysis

Only 0.35% (49,500km2) of Antarctica is ice-free. These areas are scattered around the periphery of the continent and in interior mountain ranges, making soil mapping difficult. Here we compile the results of mapping in five of the nine ice-free areas that account for 79% of the ice-free area on a reconnaissance scale and interpret the distribution of soil subgroups in Soil Taxonomy. Soils of Antarctica are contained in four orders, dominantly Gelisols (84%), 13 suborders, 27 great groups, and 76 subgroups. Forty-five percent of the soils of Antarctica are Orthels, Gelisols that show minimal cryoturbation and occur in dry landscape positions; 38% of the soils are Turbels showing cryoturbation and occurring in more moist landscape positions. Only 16% of the soils of Antarctica lack permafrost in the control section and are classified as Entisols (Gel-great groups), Inceptisols (Gelepts suborder or Gelaquepts), or Histosols (Gel-great groups). These soils occur almost exclusively along the western Antarctic Peninsula and at elevations below 30m in the South Shetland Islands (SSI) and South Orkney Islands (SOI). Typic Anhyorthels are the dominant soil subgroup comprising nearly 15,340km2, or 31% of the soils in Antarctica. These soils occur primarily in central and southern Victoria Land, but also occur in the Thiel and Pensacola Mountains and Shackleton Range, the Prince Charles Mountains, and the mountains of Queen Maud Land. Typic Haploturbels and Typic Anhyturbels occupy 14 and 13% of the soils of ice-free regions of Antarctica, respectively. Most abundant in central Victoria Land, they are common in most mountainous regions of Antarctica. The dominant soil processes of maritime Antarctica are cryoturbation, gleization, melanization, podzolization, paludization, and phosphatization. In coastal East Antarctica, the major soil processes are rubification, salinization, calcification, pervection, and gleization. The predominant soil-forming processes in the Transantarctic Mountains include rubification, salinization, desert pavement formation, and permafrost development. Measures of pedodiversity will be valuable in the selection of protected areas in Antarctica.

A soil chronosequence on Lake Mega-Frome beach ridges and its implications for late Quaternary pedogenesis and paleoenvironmental conditions in the drylands of southern Australia

The terminal lake systems of central Australia are key sites for the reconstruction of late Quaternary paleoenvironments. Paleoshoreline deposits around these lakes reflect repeated lake filling episodes and such landforms have enabled the establishment of a luminescence-based chronology for filling events in previous studies. Here we present a detailed documentation of the morphology and chemistry of soils developed in four well-preserved beach ridges of late Pleistocene and mid-to-late Holocene age at Lake Callabonna to assess changes in dominant pedogenic processes. All soil profiles contain evidence for the incorporation of eolian-derived material, likely via the formation of desert pavements and vesicular horizons, and limited illuviation due to generally shallow wetting fronts. Even though soil properties in the four studied profiles also provide examples of parent material influence or site-specific processes related to the geomorphic setting, there is an overall trend of increasing enrichment of eolian-derived material since at least ~33ka. Compared to the Holocene profiles, the derived average accumulation rates for the late Pleistocene profiles are significantly lower and may suggest that soils record important regional changes in paleoenvironments and dust dynamics related to shifts in the Southern Hemisphere westerlies.

Desert pavements as indicators of soil erosion on aridic soils in north-east Patagonia (Argentina)

Desert pavements are prominent features of many geomorphic surfaces in arid and semiarid lands. In the semiarid soils of north-eastern Patagonia, gravel cover in the shrub interspace areas of shrub-dominated communities is generally high, and contrast with that of grass-dominated patches where gravel cover is either absent or negligible. In the present study we analyze the relationship between soil erosion and desert pavement formation, in three sites, the upper, middle and lower slope positions of a flank pediment where well-conserved soils served as reference areas. We used the gravel cover and mass, as well as the thickness of the remnant A horizon, as determined by the depth of the Bt horizon of a Xeric Calciargid, as measures of soil erosion. Surface gravel at four cardinal points in respect to mounds associated with shrub-clumps was collected and the depth to the Bt horizon was determined. The mean thickness of the A horizon in the well-conserved soils were 11.3, 10.0 and 13.5 cm for the upper, middle and lower slope positions, respectively. For the same positions, the mean coarse fragment contents (> 2.0 mm) in the 0–10 cm depth of the A horizon in the well-conserved soils were 144, 92 and 119 g kg −1, and the mean surface gravel mass in the eroded patches were 5.3, 3.1 and 4.7 kg m −2. Surface gravel mass and depth of the remnant A horizon gave different estimates of the magnitude of soil erosion in the flank pediment. Thus, the mean/maximum soil loss, as determined by the mean gravel mass on the soil surface for the upper, middle and lower slope positions were, 28.3/68.2, 27.0/63.8 and 31.5/56.4 mm, respectively. These figures increased to a mean of 50.0, 52.5 and 82.0 mm for the same positions when soil loss was determined as the difference between the thickness of the A horizon of the well-conserved soil and that of the remaining A horizon in eroded patches. The loss of the A horizon by wind and water erosion seems to initiate the change from grass steppe to a stable shrub steppe characterized, in the shrub interspaces, by well-developed desert pavements. The strong correlation between surface gravel mass and the thickness of the remaining A horizon indicates that accelerated soil erosion has played an important role in the formation of desert pavements, and that desert pavements are good indicators of the extent and intensity of the erosion process in the Punta Ninfas area.

Controls on marine–erg margin cycle variability: aeolian–marine interaction in the mid‐Cretaceous Iberian Desert System, Spain

AbstractThe interaction between aeolian dunes of the Iberian erg and Tethys waters during the mid‐Cretaceous led to a variety of sedimentary facies associations such as subtidal deposits, aeolian dunes, playa lakes, coastal lakes with tidal creeks, and marshes and lagoonal embayments with tide‐influenced delta deposits. Facies associations are organized in several stacked cycles. Every cycle is defined by a sand‐drift surface separating playa lake deposits below from aeolian dune deposits above, followed by a transgressive surface separating aeolian deposits below from shallow marine deposits above. The latter are covered by playa lake deposits and finally topped by the next sand‐drift surface. Similar marine–erg margin cycles have been explained previously in terms of high‐order relative sea‐level variations (normally controlled by glacioeustasy). The studied erg margin developed during the mid‐Cretaceous which is considered to be the archetypal example of a polar ice‐free greenhouse period. This manuscript presents an alternative explanation for the cycles as caused by climate‐induced variations in the aeolian sediment supply. In this scenario, orbitally induced latitudinal shifts of the boundary between climate belts led to alternating periods of increased and decreased precipitation in the highland catchments of the back‐erg system (Variscan Iberian Massif). When climate belts shifted to lower latitudes, back‐erg highlands were under the influence of the Northern Warm Humid Belt. While arid conditions prevailed in the lowland central‐erg, increased precipitation in the highlands and the consequent recharge of ground water led to a rise of the phreatic level in the erg system; that diminished wind erosion and windblown sediment input to the fore‐erg, so that the desert margin contracted. With ongoing basin subsidence this favoured the transgression. The increased desert‐ground water flux favoured permanent coastal lakes in the fore‐erg margin and the local development of vegetation. In places where such lakes (lagoons) were connected to the sea, tidal channels were active, as seen nowadays along the desert coast of Qatar (Persian Gulf). When climate belts moved to higher latitudes, the catchment areas in the back‐erg Iberian Massif were under the influence of the Northern Hot Arid belt and a decrease of precipitation led to a drop of the phreatic level, allowing deflation of dunes and exposed wadi channel floors, and the formation of desert pavements and deflation lags in the back‐erg area; this favoured the import of large volumes of windblown sand and dust, forcing progradation of the erg and consequently a retreat of the coastline. The sand fraction accumulated in climbing aeolian dunes and dust was trapped in extensive playa lake systems. Another long‐term allocyclic control is formed by active extensional tectonics that enhanced the creation of accommodation space, especially in the first cycle. A high ground water table sustained by subsurface water supply from the Variscan Iberian Massif generated coastal fresh/brackish lakes in which tide‐influenced meandering channels and salt marshes developed. Erg margin cycles thin upward in response to a decrease of the rate of basin subsidence, suggesting that transgressions led to deep erosion of the underlying aeolian dune sands.

Desert landscape processes on a timescale of millions of years, probed by cosmogenic nuclides

Abstract Since their inception, cosmogenic nuclide methods have enhanced our understanding of Earth’s surface processes by providing a basis for directly determining surface exposure times and erosion rates of landscape elements. The ability to measure exposure ages up to several million years and erosion rates as low as a decimetre per million years means that the method is particularly useful for environments where landscapes change very slowly, such as deserts in tectonically stable regions. In this paper, we review cosmogenic nuclide studies of various aspects of desert landscapes, including regional to continental-scale landscape evolution in arid–semiarid Australia and the hyper-arid Namib, Atacama and Negev Deserts, together with mechanisms and timescales of formation of desert pavements and dune fields that have been difficult to be evaluated by other methods. The timescales revealed by these studies range beyond the Quaternary into the Miocene, and provide links between desert landscapes and late Cenozoic climate changes.

The action of wind and water in a mid-Cretaceous subtropical erg-margin system close to the Variscan Iberian Massif, Spain

Aeolian processes and ephemeral water influx from the Variscan Iberian Massif to the mid-Cretaceous outer back-erg margin system in eastern Iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements. Remains of aeolian dunes encased in ephemeral fluvial deposits (aeolian pods) demonstrate intense erosion of windblown deposits by sudden water fluxes. The alternating activity of wind and water led to a variety of facies associations such as deflation lags, desert pavements, aeolian dunes, pebbles scattered throughout dune strata, aeolian sandsheets, aeolian deposits with bimodal grain-size distributions, mud playa, ephemeral floodplain, pebble-sand and cobble-sand bedload stream, pebble–cobble-sand sheet flood, sand bedload stream, debris flow and hyperconcentrated flow deposits. Sediment in this desert system underwent transport by wind and water and reworking in a variety of sub-environments. The nearby Variscan Iberian Massif supplied quartzite pebbles as part of mass flows. Pebbles and cobbles were concentrated in deflation lags, eroded and polished by wind-driven sands (facets and ventifacts) and incorporated by rolling into the toesets of aeolian dunes. The back-erg depositional system comprises an outer back-erg close to the Variscan highlands, and an inner back-erg close to the central-erg area. The inner back-erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits. In the inner back-erg area ephemeral wadis, desiccated after occasional floods, were mud cracked and overrun episodically by aeolian dunes. Subsequent floods eroded the aeolian dunes and mud-cracked surfaces, resulting in largely structureless sandstones with boulder-size mudstone intraclasts. Floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes. The remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands. Upon desiccation, deflation resulted in lags of coarser-grained sediments. A renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions. Synsedimentary tectonics caused the outer back-erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands. Ephemeral water flow to the outer back-erg area supplied pebbles, eroded aeolian dunes, and produced hyperconcentrated flow deposits. Fluidization and liquefaction generated gravel pockets and recumbent folds. Dune damming after sporadic rains (the case of the Namib Desert), monsoonal water discharge (Thar Desert) and meltwater fluxes from glaciated mountains (Taklamakan Desert) are three potential, non-exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the Cretaceous desert margin system. An increase in relief driven by the Aptian anti-clockwise rotation of Iberia, led to an altitude sufficient for the development of orographic rains and snowfall which fed (melt)water fluxes to the desert margin system. Quartzite conglomerates and sands, dominantly consisting of quartz and well-preserved feldspar grains which are also observed in older Cretaceous strata, indicate an arid climate and the mechanical weathering of Precambrian and Palaeozoic metamorphic sediments and felsic igneous rocks. Unroofing of much of the cover of sedimentary rocks in the Variscan Iberian Massif must therefore have taken place in pre-Cretaceous times.

Characterizing arid region alluvial fan surface roughness with airborne laser swath mapping digital topographic data

Range‐front alluvial fan deposition in arid environments is episodic and results in multiple fan surfaces and ages. These distinct landforms are often defined by descriptions of their surface morphology, desert varnish accumulation, clast rubification, desert pavement formation, soil development, and stratigraphy. Although quantifying surface roughness differences between alluvial fan units has proven to be difficult in the past, high‐resolution airborne laser swath mapping (ALSM) digital topographic data are now providing researchers with an opportunity to study topography in unprecedented detail. Here we use ALSM data to calculate surface roughness on two alluvial fans in northern Death Valley, California. We define surface roughness as the standard deviation of slope in a 5‐m by 5‐m moving window. Comparison of surface roughness values between mapped fan surfaces shows that each unit is statistically unique at the 99% confidence level. Furthermore, there is an obvious smoothing trend from the presently active channel to a deposit with cosmogenic 10Be and 36Cl surface exposure ages of ∼70 ka. Beyond 70 ka, alluvial landforms become progressively rougher with age. These data suggest that alluvial fans in arid regions smooth out with time until a threshold is crossed where roughness increases at greater wavelength with age as a result of surface runoff and headward tributary incision into the oldest surfaces.

Rock varnish microlamination dating of late Quaternary geomorphic features in the drylands of western USA

Varnish microlamination (VML) dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts. In this study, we establish a generalized late Quaternary (i.e., 0–300 ka) varnish layering sequence for the drylands of western USA and tentatively correlate it with the SPECMAP oxygen isotope record. We then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late Quaternary geomorphic features in the study region. VML dating of alluvial fan deposits in Death Valley of eastern California indicates that, during the mid to late Pleistocene, 5–15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation. During the Holocene interglacial time, however, 0.5–1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate. VML dating of alluvial desert pavements in Death Valley and the Mojave Desert reveals that pavements can be developed rapidly (< 10 ky) during the Holocene (and probably late Pleistocene) in the arid lowlands (< 800 m msl) of these regions; but once formed, they may survive for 74–85 ky or even longer without being significantly disturbed by geomorphic processes operative at the pavement surface. Data from this study also support the currently accepted, “being born at the surface” model of desert pavement formation. VML dating of colluvial boulder deposits on the west slope of Yucca Mountain, southern Nevada, yields a minimum age of 46 ka for the emplacement of these deposits on the slope, suggesting that they were probably formed during the early phase of the last glaciation or before. These results, combined with those from our previous studies, demonstrate that VML dating has great potential to yield numerical age estimates for various late Quaternary geomorphic features in the western USA drylands.

Clast size controls and longevity of Pleistocene desert pavements at Lathrop Wells and Red Cone volcanoes, southern Nevada

Formation of desert pavement and accretionary soils are intimately linked in arid environments. Well-sorted fallout scoria lapilli at Lathrop Wells (75‐80 ka) and Red Cone (ca. 1 Ma) volcanoes (southern Nevada) formed an excellent parent material for pavement, allowing infiltration of eolian silt and fine sand that first clogged the pore space of underlying tephra and then aggraded and developed vesicular A (Av) horizons. Variations in original pyroclast sizes provide insight into minimum and maximum clast sizes that promote pavement and soil formation: pavement becomes ineffective when clasts can saltate under the strongest winds, while clasts larger than coarse lapilli are unable to form an interlocking pavement that promotes silt accumulation (necessary for Av development). Contrary to predictions that all pavements above altitudes of !400 m would have been reset in their development after late Pleistocene vegetation advances, the soils and pavements show clear differences in maturity between the two volcanoes. This indicates that either the pavements and/or soils develop slowly over many tens of thousands of years and then are very stable, or, if they are disrupted by vegetation advances, subsequent pavements are re-established with successively more mature characteristics.

Clast size controls and longevity of Pleistocene desert pavements at Lathrop Wells and Red Cone volcanoes, southern Nevada

Research Article| July 01, 2006 Clast size controls and longevity of Pleistocene desert pavements at Lathrop Wells and Red Cone volcanoes, southern Nevada Greg A. Valentine; Greg A. Valentine 1Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar Charles D. Harrington Charles D. Harrington 1Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Greg A. Valentine 1Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Charles D. Harrington 1Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Publisher: Geological Society of America Received: 13 Dec 2005 Revision Received: 09 Feb 2006 Accepted: 03 Apr 2006 First Online: 09 Mar 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 The Geological Society of America, Inc. Geology (2006) 34 (7): 533–536. https://doi.org/10.1130/G22481.1 Article history Received: 13 Dec 2005 Revision Received: 09 Feb 2006 Accepted: 03 Apr 2006 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Greg A. Valentine, Charles D. Harrington; Clast size controls and longevity of Pleistocene desert pavements at Lathrop Wells and Red Cone volcanoes, southern Nevada. Geology 2006;; 34 (7): 533–536. doi: https://doi.org/10.1130/G22481.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Formation of desert pavement and accretionary soils are intimately linked in arid environments. Well-sorted fallout scoria lapilli at Lathrop Wells (75–80 ka) and Red Cone (ca. 1 Ma) volcanoes (southern Nevada) formed an excellent parent material for pavement, allowing infiltration of eolian silt and fine sand that first clogged the pore space of underlying tephra and then aggraded and developed vesicular A (Av) horizons. Variations in original pyroclast sizes provide insight into minimum and maximum clast sizes that promote pavement and soil formation: pavement becomes ineffective when clasts can saltate under the strongest winds, while clasts larger than coarse lapilli are unable to form an interlocking pavement that promotes silt accumulation (necessary for Av development). Contrary to predictions that all pavements above altitudes of ∼400 m would have been reset in their development after late Pleistocene vegetation advances, the soils and pavements show clear differences in maturity between the two volcanoes. This indicates that either the pavements and/or soils develop slowly over many tens of thousands of years and then are very stable, or, if they are disrupted by vegetation advances, subsequent pavements are re-established with successively more mature characteristics. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Pedogenesis of Vesicular Horizons, Cima Volcanic Field, Mojave Desert, California

An existing model of desert pavement formation suggests desert pavement clasts rise vertically on an accreting eolian mantle and the underlying vesicular horizon coevolves with pavement formation. Results presented here support this model and provide a mechanism whereby eolian material is transported from the ground surface to ped interiors, thereby increasing the thickness of the vesicular horizon underlying desert pavements. Basaltic desert pavements in the Cima Volcanic Field are underlain by a vesicular horizon with strong coarse columnar and strong medium platy soil structure. Peds collected from three sites along a topographic gradient were subsampled into seven ped domains to quantify physical, chemical, and micromorphological properties within peds and along the topographic transect. Ped interiors have up to 40% clay and 12% CaCO3 whereas sediments adhering to ped sides have &lt;7% clay and 2% CaCO3 Argillans and siltans lining platy surfaces in ped centers and bottoms indicate desert dust is translocated vertically along the macropores between peds and horizontally along platy boundaries to ped interiors. Once soils develop a strong columnar and platy structure, translocation to ped interiors is enhanced. Calibrated radiocarbon ages between 5440 and 5045 BP for Av ped centers suggest enhanced dust flux and pedogenesis occurred during the drier middle Holocene, an inference supported by luminescence dating and correlations with regional eolian chronologies.

Pedogenesis of Vesicular Horizons, Cima Volcanic Field, Mojave Desert, California

An existing model of desert pavement formation suggests desert pavement clasts rise vertically on an accreting eolian mantle and the underlying vesicular horizon coevolves with pavement formation. Results presented here support this model and provide a mechanism whereby eolian material is transported from the ground surface to ped interiors, thereby increasing the thickness of the vesicular horizon underlying desert pavements. Basaltic desert pavements in the Cima Volcanic Field are underlain by a vesicular horizon with strong coarse columnar and strong medium platy soil structure. Peds collected from three sites along a topographic gradient were subsampled into seven ped domains to quantify physical, chemical, and micromorphological properties within peds and along the topographic transect. Ped interiors have up to 40% clay and 12% CaCO3 whereas sediments adhering to ped sides have <7% clay and 2% CaCO3 Argillans and siltans lining platy surfaces in ped centers and bottoms indicate desert dust is translocated vertically along the macropores between peds and horizontally along platy boundaries to ped interiors. Once soils develop a strong columnar and platy structure, translocation to ped interiors is enhanced. Calibrated radiocarbon ages between 5440 and 5045 BP for Av ped centers suggest enhanced dust flux and pedogenesis occurred during the drier middle Holocene, an inference supported by luminescence dating and correlations with regional eolian chronologies.

Field and computer simulation experiments on the formation of desert pavement

A series of rainfall simulation experiments was carried out at the Walnut Gulch Experimental Watershed, Tombstone, Arizona (31° 43′N, 110° 41′W), to observe the speed at which desert pavement surfaces could be re-established following disturbance. The results of these experiments, which consisted of repeated, 5 min rainfall events, demonstrate that pavements can reform within 10 events, which is compatible with observations of the recovery of surfaces under natural rainfall on an annual cycle. A model for the development of pavements by raindrop erosion processes had previously shown the importance of these processes. The rainfall simulation experiments were used to test the general applicability of this model. The model was able to reproduce the general characteristics of the regenerated surfaces and the timing of their development. However, details of the particle size fractions produced were less well simulated by the model. Testing of the sensitivity of the model to the sediment transport parameters suggests that this problem is not related to the soil characteristics, but is more likely to be an indication of a poor understanding of all the feedbacks operating in the raindrop erosion processes. Copyright © 1999 John Wiley & Sons, Ltd.

Field and computer simulation experiments on the formation of desert pavement

A series of rainfall simulation experiments was carried out at the Walnut Gulch Experimental Watershed, Tombstone, Arizona (31° 43′N, 110° 41′W), to observe the speed at which desert pavement surfaces could be re-established following disturbance. The results of these experiments, which consisted of repeated, 5 min rainfall events, demonstrate that pavements can reform within 10 events, which is compatible with observations of the recovery of surfaces under natural rainfall on an annual cycle. A model for the development of pavements by raindrop erosion processes had previously shown the importance of these processes. The rainfall simulation experiments were used to test the general applicability of this model. The model was able to reproduce the general characteristics of the regenerated surfaces and the timing of their development. However, details of the particle size fractions produced were less well simulated by the model. Testing of the sensitivity of the model to the sediment transport parameters suggests that this problem is not related to the soil characteristics, but is more likely to be an indication of a poor understanding of all the feedbacks operating in the raindrop erosion processes. Copyright © 1999 John Wiley & Sons, Ltd.

The use of Landsat Thematic Mapper data for mapping and correlation of Quaternary geomorphic surfaces in the southern Whipple Mountains, California

Alluvial geomorphic surfaces in the southern Whipple Mountains (south-eastern California) were mapped using Landsat Thematic Mapper (TM) data. Surfaces can readily be classified as young, intermediate or old in terms of stages of development. Spectral and textural information contained in these data are interpretable in terms of source rock composition, degree of desert pavement formation and drainage patterns, which are among the most important criteria used in field-based classification. Thus, classification and mapping of geomorphic surfaces based on image analysis is directly comparable to maps produced from field-based observations, potentially providing information about climate and neotectonics.

Effects of vegetation change on interrill runoff and erosion, Walnut Gulch, southern Arizona

During the past 100 years grassland has been replaced by shrubland in many parts of the American Southwest. The effects of this vegetation change on interrill runoff and erosion are investigated by performing field experiments on small and large runoff plots located on contemporary grassland and shrubland hillslopes in Walnut Gulch Experimental Watershed. The experiments indicate that the vegetation change causes runoff and erosion to increase in interrill areas by decreasing resistance to overland flow, decreasing runon infiltration, increasing the spatial heterogeneity of the plant canopy, and possibly increasing the susceptibility of the soil to frost action. Increased runoff and erosion result in stripping of the soil A horizon, the formation of desert pavement in intershrub areas, and the development of rills. Fines remain and accumulate only under shrubs, where they form islands of fertility. Shrubs are able to regenerate in these islands, but it is difficult for any plants to become established in intershrub areas. Consequently, there is an increase in the spatial heterogeneity of soil resources, and this spatial heterogeneity is self-perpetuating. Increasing spatial heterogeneity of soil resources is considered to be characteristic of the process of desertification.