Deflation Basin Research Articles

Spatial–temporal evolution of aeolian blowout dunes at Cape Cod

This paper explores historical evolution of blowouts at Cape Cod National Seashore (CCNS), USA — a site that hosts one of the world's highest densities of active and stabilized blowouts. The Spatial–Temporal Analysis of Moving Polygons (STAMP) method is applied to a multi-decadal dataset of aerial photography and LiDAR to extract patterns of two-dimensional movement and morphometric changes in erosional deflation basins and depositional lobes. Blowout development in CCNS is characterized by several geometric (overlap) and movement (proximity) responses, including: i) generation and disappearance, ii) extension and contraction, iii) union or division, iv) clustering and v) divergence by stabilization. Other possible movement events include migration, amalgamation and proximal stabilization, but they were not observed in this study. Generation events were more frequent than disappearance events; the former were highest between 1985 and 1994, while the latter were highest between 2000 and 2005. High rates of areal change in erosional basins occurred between 1998 and 2000 (+3932m2a−1), the lowest rate (+333m2a−1) between 2005 and 2009, and the maximum rate (+4589m2a−1) between 2009 and 2011. Union events occurred mostly in recent years (2000–2012), while only one division was observed earlier (1985–1994). Net areal changes of lobes showed gradual growth from a period of contraction (−1119m2a−1) between 1998 and 2000 to rapid extension (+2030m2a−1) by 2010, which is roughly concurrent with rapid growth of erosional basins between 2005 and 2009. Blowouts extended radially in this multi-modal wind regime and, despite odd shapes initially, they became simpler in form (more circular) and larger over time. Net extension of erosional basins was toward ESE (109°) while depositional lobes extended SSE (147°). Lobes were aligned with the strongest (winter) sand drift vector although their magnitude of areal extension was only 33% that of the basins. These differences in extension responses likely result from more complex and evolving flow-form interactions inside erosional basins. Historical photographs and CCNS documents suggest that blowout evolution may be influenced by land-use changes, such as revegetation campaigns in 1985 that were followed by high blowout generation. High magnitude regional storm events (e.g., hurricanes) also play a role. The analytical framework presented provides a systematic means for two-dimensional geomorphic change detection and pattern analysis that can be applied to other landscapes.

Aeolian responses to climate variability during the past century on Mesquite Lake Playa, Mojave Desert

The erosion and deposition of sediments by wind from 1901 to 2013 have created large changes in surface features of Mesquite Lake playa in the Mojave Desert. The decadal scale recurrence of sand-sheet development, migration, and merging with older dunes appears related to decadal climatic changes of drought and wetness as recorded in the precipitation history of the Mojave Desert, complemented by modeled soil-moisture index values. Historical aerial photographs, repeat land photographs, and satellite images document the presence and northward migration of a mid-20th century sand sheet that formed during a severe regional drought that coincided with a multi-decadal cool phase of the Pacific Decadal Oscillation (PDO). The sand sheet slowly eroded during the wetter conditions of the subsequent PDO warm phase (1977–1998) due to a lack of added sediment. Sand cohesion gradually increased in the sand sheet by seasonal additions of salt and clay and by re-precipitation of gypsum, which resulted in the wind-carving of yardangs in the receding sand sheet. Smaller yardangs were aerodynamically shaped from coppice dunes with salt-clay crusts, and larger yardangs were carved along the walls and floor of trough blowouts. Evidence of a 19th century cycle of sand-sheet formation and erosion is indicated by remnants of yardangs, photographed in 1901 and 1916, that were found buried in the mid-20th century sand sheet. Three years of erosion measurements on the playa, yardangs, and sand sheets document relatively rapid wind erosion. The playa has lowered 20 to 40cm since the mid-20th century and a shallow deflation basin has developed since 1999. Annually, 5–10cm of surface sediment was removed from yardang flanks by a combination of wind abrasion, deflation, and mass movement. The most effective erosional processes are wind stripping of thin crusts that form on the yardang surfaces after rain events and the slumping of sediment blocks from yardang flanks. These wind-eroded landforms persist several decades to a century before eroding away or being buried by younger sands. On Mesquite Lake playa the climatic history of alternating PDO phases of multi-decadal drought and wetness is recorded twice by the presence of yardangs formed nearly a century apart.

A review of Late Quaternary inland dune systems of South America east of the Andes

Inland dune systems of South America occur in a variety of environmental settings under different climatic conditions, from humid–subhumid to semiarid–arid. This contribution provides the state of the art on dune research of inland systems east of the Andes. Tropical northern (∼10°N–∼10°S), including the dune fields of Llanos del Orinoco and the Amazonian basin, are mainly formed from parabolic, blowout (or deflation basins) and linear dunes, developed on river floodplains. Aeolian activity was reported to occur near the late Pleistocene–Holocene boundary in Llanos del Orinoco, over the last ∼17 ka in the Branco river basin and ∼32.6 ka in the Negro river basin, both in the Amazonian region. In general, the attributed aeolian origin is controversial, the morphology difficult to determine, and the chronology still extremely limited and rather debatable in some cases. The southern tropical region (∼10°S–∼22°S) includes aeolian systems situated across the extensive lowlands of the Gran Chaco and those located in fluvial basins related to the cratonic Brazilian shield (São Francisco River, Pantanal and Mato Grosso). The oldest barchanoid–barchan ridges at the Gran Chaco were dated ∼36–33 ka and subsequent aeolian sand accumulation occurred at ∼18 ka, ∼14–12 ka, ∼10–9 ka and mid to late Holocene times. Parabolic dunes at the São Francisco River floodplain show an oldest episode generated between ∼28 and ∼11 ka, followed by eolian activity during the early to mid-Holocene. No chronological data is available for the linear and lunette dunes described at the Pantanal. Linear ridges were distinguished in the upper Paraná River (Mato Grosso) with associated sand accumulation at different intervals of the Holocene. The last reviewed region is the Andean Piedmont and western Pampas, at subtropical eastern South America, comprising a large variety of dune morphologies (barchan–barchanoid, linear, parabolic, transverse and lunette dunes, deflation basins, and sand sheets). Luminescence ages suggest the occurrence of aeolian activity intervals during late glacial times and the Holocene. The general understanding on the dynamic of South American dune systems is hampered by the paucity of chronological information and the representativeness of some dune records. Whether they reflect local or regional environmental conditions is still a matter of discussion in several areas that need further studies.

Airflow and aeolian sediment transport patterns within a coastal trough blowout during lateral wind conditions

ABSTRACTBlowouts are depressions that occur on coastal dunes, deserts and grasslands. The absence of vegetation in blowouts permits high speed winds to entrain and remove sediment. Whereas much research has examined patterns of wind flow and sediment transport on the stoss slopes and lee of sand dunes, no study has yet investigated the connections between secondary air‐flow structures and sediment transport in a blowout where zones of streamline compression, expansion and steering are less clearly delineated. In this study we investigated the variability of sediment flux and its relation to near‐surface wind speed and turbulence within a trough blowout during wind flow that was oblique to the axis of the blowout. Wind flow was measured using six, three‐dimensional (3D) ultrasonic anemometers while sediment flux by eight sand traps, all operating at 25 Hz.Results demonstrated that sediment flux rates were highly variable throughout the blowout deflation basin, even over short distances (< 0.5 m). Where flow was steadiest, flux was greatest. Consequently the highest rates of sediment transport were recorded on the erosional wall crest where flow was compressed and accelerated. The strength of correlation between sediment flux and wind parameter improved with an increase in averaging interval, from 10 seconds to 1 minute. At an interval of 10 seconds, however, wind speed correlated best with flux at seven of eight traps, whereas at an interval of one minute Turbulent Kinetic Energy (TKE) provided the best correlation with flux at six of the eight traps. Correlation between sediment flux and wind parameters was best in the centre of the blowout and poorest on the erosional wall crest. The evidence from this paper suggests, for the first time, that TKE may be a better predictor of sediment transport at minute scale averaging intervals, particularly over landforms where wind flow is highly turbulent. Copyright © 2014 John Wiley & Sons, Ltd.

High resolution measured and modelled three-dimensional airflow over a coastal bowl blowout

Blowouts are common landforms found within coastal dunes. Their dynamics are primarily driven by aeolian transport caused by surface wind stress, though patterns of deflation and deposition within blowouts are poorly understood as near surface wind flow is complex. Three‐dimensional wind flows around blowouts have yet to be properly quantified, especially within zones of separation, re-attachment and acceleration. This has been largely due to inadequate measurement of airflow and a lack of suitable airflow models. With this in mind, we present results from a study that has quantified alongshore and oblique onshore wind flow dynamics over a bowl blowout on the Belmullet Peninsula, Ireland. Using ultrasonic three-dimensional anemometry (measuring at 50Hz) and three-dimensional computational fluid dynamic (CFD) modelling, we measure and model for the first time in 3D a detailed picture of the heterogeneity of wind flow over this type of terrain.During alongshore wind conditions, wind speeds within the deflation basin were retarded by 50% compared to the foredune zone and flow separation restricted to a small zone in lee of the windward rim. Wind was directed into the deflation basin through a gap in a western erosional wall, termed the blowout throat. In oblique onshore wind, airflow orientated with the blowout throat remained unchanged in direction and slowed by only 30% compared to wind speed on the foredune. In lee of the erosional wall adjacent to the blowout throat, small zones of flow separation occurred close to the erosional wall. In both cases, the highest variation in wind speed and direction occurred in zones of separation and attachment whilst flow increased in steadiness with height over the erosional walls. The results illustrate that wind is manipulated according to localised topography within the bowl blowout itself. Resulting zones of potential sediment transport (erosion and deposition) are spatially complex and alter with wind direction. The presence of a blowout throat has a significant influence on airflow patterns within a deflation basin. Modelled (CFD) and measured anemometer data demonstrated excellent comparisons for wind direction and speed, allowing much greater spatial measurement resolution than physical instrumentation. Simulated turbulence did not correlate well with measured data, highlighting the requirement for high frequency, three-dimensional anemometry in areas of complex flow.

Form–flow interactions of an aeolian saucer blowout

AbstractAirflow patterns through a saucer blowout are examined from wind speed and direction measurements made during a chinook wind event. The blowout long‐axis is oriented east–west with a broad depositional apron on the east side. Wind directions during the event rotated from south‐westerly to westerly, permitting an assessment of oblique and axis‐parallel flows. Results show that airflow passing over the windward rim of the saucer blowout expands and decelerates, leading to flow separation and a small re‐circulation zone on sheltered lee slopes. Near the deflation basin, airflow re‐attaches to the blowout surface and accelerates up to a small opening in the east rim, where it can be up to 50% faster than on the windward edge. Beyond the downwind rim the airflow expands and decelerates and sand is deposited onto a broad apron. Similar to coastal trough blowouts, the degree of airflow steering and acceleration along the deflation basin is determined by the angle of incidence between the approach wind and the long‐axis of the blowout. As the angle of incidence increases wind speed accelerates at 0·3 m above the surface of the deflation basin and the degree of airflow steering increases. Overall, a two‐fold process is identified, where south‐westerly flows have greater potential for eroding the deflation basin, while westerly flows have greater potential for evacuating sand from within the blowout. Visual observations indicate that sand eroded from the deflation basin during south‐westerly flows is re‐distributed to adjacent zones of low wind speed until axis‐parallel winds evacuate the sand through the opening in the east rim. Morphometric changes since 1994 indicate that the blowout morphology has remained relatively constant, suggesting a persistent interplay between oblique and axis‐parallel wind erosion events. Collectively, these findings indicate that the angle of approach winds is an important control on saucer blowout morphodynamics. Copyright © 2009 John Wiley & Sons, Ltd.

Spatial and temporal patterns of aeolian sediment transport on an inland parabolic dune, Bigstick Sand Hills, Saskatchewan, Canada

Topographic changes from erosion pins and on-site meteorological data document the spatial and temporal patterns of aeolian sediment transport at monthly to annual timescales across an active parabolic dune within a vegetation-stabilized inland, prairie dune field. Over two years, the sediment budget, calculated from digital elevation models, shows that the total volume of erosion (9890 m 3) is greater than the amount of deposition (6990 m 3), indicating a net loss of 2900 m 3 of sediment (or ∼ 29% of eroded sediment) from the dune. Sediment erosion occurred mainly on the stoss slope (3600 m 3; ∼ 36% of eroded sediment), but also on the south (2100 m 3; ∼ 21%) and north sides of the dune head (1700 m 3; ∼ 17%), the blowouts along the arms (1740 m 3, ∼ 18%) and the crest (650 m 3; ∼ 7%). Erosion from the deflation basin is limited by surface roughness and armoring effects of a gravel lag deposit (100 m 3; ∼ 1%). Thus, the blowouts currently contribute to maintaining dune mobility because no other sediment input occurs from upwind. Sediment deposition onto the dune occurred primarily beyond the brink on the south and southeast lee slopes (5500 m 3; ∼ 80%), coinciding with the southeasterly resultant transport direction for November 2004–05. The net loss of about 2900 m 3 (∼ 29%) may be attributed to sediment carried in suspension over and beyond the dune. Correlation analysis between sediment transport and meteorological variables suggests that monthly to seasonal changes of surface conditions (e.g., vegetation cover, ground freezing, moisture) buffer the relative importance of temperature and precipitation on rates of sediment transport. Conversely, wind correlates well on a monthly to seasonal basis because it is a driver of transport under all types of surface conditions. Seasonal effects produce a complex interaction between wind, climate and surface conditions. This leads to a dynamic range of threshold velocities, which in turn causes spatial and temporal variations in transport-limiting and supply-limiting conditions. Collectively, these findings have implications for modeling parabolic dune morphodynamics and sediment transport in mid- to high-latitude inland settings.

The 410,000 year terrestrial age of eucrite Río Cuarto 001

Abstract— We have measured a surprisingly long terrestrial age of 410,000 ±45,0020,000 yr (410 ±2045ka) for basaltic eucrite Río Cuarto 001 using accelerator mass spectrometry of 26Al, 36Cl, and 41Ca. Though many meteorites are known to have survived for tens or hundreds of ka in Antarctica or hot deserts, the mean annual precipitation of 815 mm in Río Cuarto, Cordoba Province, Argentina, makes the long survival of this meteorite remarkable. We propose two explanations for the exceptional preservation of Río Cuarto 001. First, the meteorite contains only trace amounts of metal, so the weathering and oxidation of metallic Fe, which commonly destroys chondrites, is ineffective in this case. Second, the meteorite was found in a relatively young deflation basin, and may have been exhumed only recently from beneath a protective layer of soil. Insofar as the survival on Earth of Río Cuarto 001 is due to environmental factors, there may be other meteorites with comparably long terrestrial ages still to be discovered in the vicinity.

Synthesis of a new conceptual model to facilitate management of ephemeral deflation basin lakes

AbstractEphemeral deflation basin lakes are widespread throughout arid and semiarid regions of the Murray–Darling Basin in Australia. Although they are diverse, productive habitats, the water resources development has generally caused significant declines in their ecological condition. Managers are currently trying to protect or restore these systems, however, without an adequate theoretical framework on which to base management decisions. This is because the existing conceptual models provide little insight into the effects of any component of the flow regime except flooding. This paper reviews the effects of flooding and drying on lakes, using the information and conclusions therein to propose a conceptual model that identifies five stages in the flooding and drying cycle. This conceptual model incorporates elements of the Flood Pulse Concept, Trophic Cascade models and the Geomorphic–Trophic model, as they apply to these highly variable water systems.

Morphodynamics and climate controls of two aeolian blowouts on the northern Great Plains, Canada

AbstractBlowouts are the most regionally pervasive active aeolian landform on the northern Great Plains of North America. This study reports a long‐term investigation into the morphological development of two adjacent blowouts in a continental dune field. The blowouts were monitored for a decade in the Bigstick Sand Hills of southwestern Saskatchewan, Canada. Topographic changes were determined from dense arrays of erosion pins in each blowout (1 per 4 m2, n = 171; and 1 per 16 m2, n = 150). Pin measurements were made 16 times between May 1994 and May 2004. Over the decade both blowouts expanded and more than doubled in volume. Differences in form–flow interactions have caused the larger of the two blowouts to deposit more than a metre of sediment within the deflation basin, and the smaller blowout to erode by more than a metre. A negative feedback effect was triggered when the larger blowout reached a critical size around 1994 (60 m × 36 m × 8·1 m, length × width × height) when sediment was no longer eroded from the deflation basin. A positive feedback in the smaller blowout continues to facilitate erosion from the deflation basin. Monthly observations since 2002 indicate that aspect plays an important role in the development of these blowouts by creating a spatial asymmetry in sediment availability. Sediment is more readily available throughout the year on south‐facing slopes, which receive greater insolation than north‐facing slopes and are often drier and more frequently thawed in this cold‐climate environment. Comparisons between climate data from a remote meteorological station 45 km to the southwest and sediment transport indices developed from the erosion pin data produced very few correlations significant at the 95 per cent confidence level. Nevertheless, the signs of the correlation coefficients indicate that sediment erosion and deposition in both blowouts respond similarly to the following climate variables recorded at the remote station: (i) the amount of precipitation, (ii) the transport capacity of the wind and (iii) transporting winds from a directional wedge between 180 and 330°. Taken altogether, the results from this study highlight the importance of climate and feedback effects in blowout development that may be extended to other blowouts in continental and coastal settings. Copyright © 2006 John Wiley & Sons, Ltd.

The Hot Tubb Folsom-Midland Site (41CR 10), Texas

The Hot Tubb site, located in the Monahans Dunes just off the southern High Plains of west Texas, has yielded Folsom and Midland projectile points, as well as badly fragmented and occasionally burned remains of Bison antiquus. Because these materials occur primarily on the surface of a deflation basin within an active sand dune, which also contains artifacts of later age, the Paleoindian component cannot be easily isolated, nor have attempts to determine its radiocarbon age been successful. Nonetheless, the distribution and density of the bone and diagnostic Folsom material indicate there is spatialandpossibly stratigraphic integrity to this component, which makes it possible to discern where and what Paleoindian activity may have occurred on site.We infer this was a small Folsom-age bison kill and processing locality of an estimated six animals. The lithic assemblage is marked by intensive reworking and even refluting of projectile points, suggesting that the supply of stone, originally acquired at sources at least 150 km distant, was low by the time of this occupation. That dearth of stone, the presence of Midland points, as well as a possible Midland point preform, may also shed some light on the longstanding ‘Folsom-Midland Problem.’

The Holocene history of the White Sands dune field and influences on eolian deflation and playa lakes

White Sands National Monument is the world's largest gypsum dune field. The dunes are downwind of a 20-m-deep, 19-km-wide deflation basin containing large playa lakes. Today, the gypsum sand is derived from the edge of the deflation basin, next to the dune field, rather than the alkali flat and playa lakes, where gypsum crystals are forming. Three erosional shorelines mark wetter episodes, when playa lakes formed in the deflation basin. Successively, younger shorelines formed within older ones as the basin deepened, but was not widened by deflation. The modern shoreline is forming around Lake Lucero Playa. The oldest shoreline, termed L1, is degraded and formed near the Pleistocene–Holocene transition. Deflation from the L1 to the L2 shoreline cut through Pleistocene bedded evaporites and probably marks initiation of the dune field. This event was before 5840 yr BP , based on radiocarbon dates. This reinforces an evolving consensus that episodes of deflation have characterized desert basins in the southwestern United States. Regional deflation events have been dated at 7000 and 4000 yr BP . The shorelines imply the White Sands dune field was created in short episodes and the modern dune field may not represent conditions during expansion of the dune sea.

The effects of drying and re‐flooding on nutrient availability in ephemeral deflation basin lakes in western New South Wales, Australia

AbstractWe examined the response of nutrient concentrations to the drying and re‐flooding of ephemeral deflation basin lakes (EDBL) in western New South Wales, Australia. As lakes dried total nitrogen (TN) and total phosphorus (TP) concentrations increased. TN concentrations increased more quickly and TP concentrations increased more slowly than could be attributed to evaporation alone. This suggested that additional nitrogen was being sequestered from the atmosphere or sediments and that some phosphorus loss to the sediments was occurring. Concentrations of nitrogen oxides (NOx) and filterable reactive phosphorus (FRP), however, declined as lakes dried, suggesting a tighter coupling of nutrient release and uptake mechanisms. Inorganic nutrient concentrations rose sharply in response to re‐flooding in all lakes. Evidence is provided to suggest that post‐flood nutrient pulses are the net result of both riverine inputs and sediment releases and that the relative significance of either may be influenced by regulation. Copyright © 2002 John Wiley & Sons, Ltd.

Microbial and Plant Community Structure Across a Primary Succession Gradient

The formation of the organic layer within Scandinavian forest soil started about 10000 yr ago, following the retreat of the continental ice sheet. Since then the land has been slowly rising in northern Europe and uplift still occurs on the coast of the Bothnian Bay at a rate of about 0.6-0.9 m per 100 yr. Four, 300 m long, successional gradients were studied from the shoreline to a Scots pine (Pinus sylvestris) stand with a fully developed humus layer of a few centimetres' thickness. The plantless shoreline was followed by small foredunes and dunes, characterized by Agrostis stolonifera and Leymus arenarius, respectively, and the deflation basin characterized by lichens and sparse Festuca ovina and Deschampsia flexuosa. The study sites situated in Scots pine stands of about 25 and 40 yr age were characterized by sparse dwarf shrubs, lichens and bryophytes. The amount of organic matter in soil increased along the gradient. When the microbial biomass, estimated as indicative phospholipid fatty acids (PLFAs), was calculated on the organic matter basis, the total microbial biomass as well the amount of bacterial PLFAs decreased from the earlier stages of succession towards the pine forest. The ratio of fungal to bacterial PLFAs increased along the succession. The bacterial community structure in the shore soil was different to that in the dune soil or in forested zones. On the plantless shore the microbial community was almost completely described by PLFAs indicative of Gram-negative bacteria. In addition to these bacterial PLFAs, dunes were characterized by PLFAs indicative of actinomycetes. Thus, the fungal part of the microbial community seemed to respond most to the accumulation of organic matter and increasing C/N ratio, while the bacterial biomass and bacterial community structure seemed also to reflect the composition of the vegetation and the varying quality of the organic matter.

Flow dynamics and geomorphology of a trough blowout

ABSTRACTThe dynamics and geomorphological development of a trough blowout located at Fiona Beach in the Myall Lakes National Park in NSW, Australia, are examined. Wind speeds, velocities and flow structure were measured utilizing an array of miniature Rimco cup anemometers, Gill bivane and UVW instruments, and wind vanes. Flow measurements indicate that when the wind approaches the trough blowout parallel to the throat orientation, jets occur both in the deflation basin and along the erosional walls, relative flow deceleration and expansion occurs up the depositional lobe, jets are formed over the depositional lobe crest accompanied by downwind flow separation on the leeward side of the lobe, and flow separation and the formation of corkscrew vortices occur over the crests of the erosional walls. Maximum erosion and transport occurs up the deflation basin and onto the depositional lobe. Trough blowout morphologies are explained as a function of these flow patterns.When the wind approaches the blowout obliquely, the flow is steered considerably within the blowout, and the degree and complexity of topographic steering is dependent on the blowout topography. The flow is usually extremely turbulent and large corkscrew vortices are common. The local topography of a blowout can be very important in determining overall sand transport and blowout evolutionary conditions and paths.Estimates of potential sand transport within the blowout may be up to two orders of magnitude lower than actual rates if remotely sensed wind data are used.

Flow dynamics in a trough blowout

The dynamics and geomorphological development of a trough blowout located at Fiona Beach in the Myall Lakes National Park in NSW, Australia are examined. Wind velocities and flow structure were measured utilising an array of miniature Rimco cup anemometers, Gill bi-vane and UVW instruments, and wind vanes. Flow measurements indicate that when the wind approaches the trough blowout parallel to the throat orientation, jets occur both in the deflation basin and along the erosional walls, relative flow deceleration and expansion occur up the depositional lobe, jets are formed over the depositional lobe crest accompanied by downwind flow separation on the leeward side of the lobe, and flow separation and the formation of corkscrew vortices occur over the crests of the erosional walls. Maximum erosion and transport occur up the deflation basin and onto the depositional lobe. Trough blowout morphologies are explained as a function of these flow patterns. When the wind approaches the blowout obliquely, the flow is steered considerably within the blowout. The degree and complexity of topographic steering is dependent on the blowout topography. The flow is usually extremely turbulent and large corkscrew vortices are common. The local topography of a blowout can be very important in determining flow patterns, overall sand transport and blowout evolutionary conditions and paths. Estimates of potential sand transport within the blowout may be up to two orders of magnitude lower than actual rates if remote wind data are used.

Deflation and redeposition of sand dunes in finnish lapland

Deflation and redeposition of aeolian sands in Finnish Lapland have been studied by analysis of their sedimentology and stratigraphy, by dating buried charcoal layers, and by obtaining TL dates. The thickness of redeposited sands on buried soils ranges from a few decimetres to more than two metres. Original dune formation after deglaciation finished around 7000 BP. Subsequent aeolian activity has been mainly destructive in nature. Deflation started in some regions about 4800 BP, continuing with several breaks until the present. Some deflation basins have stayed active for at least 1300 years. However, it is too early to draw general conclusions for the whole area. Forest fires have been important reactivators of aeolian sand drift, but tend to be rather local events. Change in the ground water table is a basic factor affecting deflation. At present, human impact and overgrazing by reindeer seem to increase deflation.

The age of the meteorite recovery surfaces of Roosevelt County, New Mexico, USA

Abstract— We have obtained minimum age estimates for the sand units underlying the two largest meteorite deflation surfaces in Roosevelt County, New Mexico, USA, using thermoluminescence dating techniques. The dates obtained ranged from 53.5 (±5.4) to 95.2 (±9.5) ka, and must be considered lower limits for the terrestrial ages of the meteorites found within these specific deflation surfaces. These ages greatly exceed previous measurements from adjacent meteorite‐producing deflation basins. We find that Roosevelt County meteorites are probably terrestrial contemporaries of the meteorites found at most accumulation zones in Antarctica. The apparent high meteorite accumulation rate reported for Roosevelt County by Zolensky et al. (1990) is incorrect, as it used an age of 16 ka for all Roosevelt County recovery surfaces. We conclude that the extreme variability of terrestrial ages of the Roosevelt County deflation surfaces effectively precludes their use for calculations of the meteorite accumulation rate at the Earth's surface.

Ecological processes and plant adaptations on coastal dunes

This paper examines the stresses on coastal plants and plant adaptations imposed in the coastal dune environment. The coastal dune ecosystem experiences severe stresses in the form of salt spray, sand burial, swash inundation, dryness, high light intensity, wind exposure, soil salinity and nutrient deficiency. Common adaptations to these stresses include salt resistance, positive growth response to burial, flooding resistance, leaf roll, photosynthesis, salt bladders, nitrogen fixation, variation of life cycle, germination strategies, and plant morphology to name a few. The level of these stresses is highest in the beach–foredune environment and generally decreases with distance from the coast in fully vegetated coastal dune systems (e.g. relict foredune plains). Plant succession and generally species richness tend to follow these landward-decreasing trends. Blowouts disrupt the most simple systems. Parabolic dunes, when active, display reversed-succession landward trends compared to foredunes and locally disjunct lateral species patterns. Transgressive (mobile) dunefields experience high stress levels (principally a mobile substrate) and locally, slack and deflation basins add cement pavement or standing water stresses. Microenvironments and local habitats are generally lowest on foredunes, moderate on blowouts and parabolics, and highest on transgressive dunefields. On a global scale, warm temperature coasts generally display the highest species richness, lowest stress levels overall, and possibly lowest number of endemic species. As semi-aridity and aridity on coasts increase, there is a trend towards increasing stress levels, lower species richness (particularly in foredunes), less foredune, relict foredune and parabolic dune development, increasing development of transgressive dunefields, less plant cover, more endemic species, and an increasing mixture of desert and coastal species. This paper is dedicated to the memory of Derek Ranwell.

Lea County 001, an H5 chondrite, and Lea County 002, an ungrouped type 3 chondrite

Abstract— A search of active deflation basins near Jal, Lea County, New Mexico resulted in the discovery of two meteorites, Lea County 001 and 002. Lea County 001 has mean olivine and low‐Ca pyroxene compositions of Fa19 and Fs17, respectively. These and all other mineralogical and petrological data collected indicate a classification of H5 for this stone. Lea County 002 has mean olivine and low‐Ca pyroxene compositions of Fa2 and Fs4, and is unequilibrated. Although it is mineralogically most similar to Kakangari and chondritic clasts within Cumberland Falls, the high modal amount of forsterite makes Lea County a unique type 3 chondrite. Oxygen isotope data for Lea County 002 fall on an 16O‐mixing line through those of the enstatite meteorites and IAB irons, a feature shared by Kakangari.