Deflation Plains Research Articles

The Formation of Deflation Ridges

The deposition of both pumice and shell is common on beaches during calm and storm wave conditions. This paper describes an investigation of pumice and shell ridges at two sites in Australia, Dark Point in NSW, and in the Younghusband Peninsula in SE South Australia. The formation of lines of wave formed shelly and pumice rich deposits on, and above the backshore is described. The deposits are buried by dune development, but then later exhumed by aeolian deflation as deflation plains and basins evolve. Aeolian erosion of the finer sandy sediments leads to the creation of a ridge form, herein termed a deflation ridge. A new schematic model of ridge formation is also detailed whereby deflation ridges are formed by the aeolian erosion and deflation of shell or pumice concentrations and lag deposits.

Catastrophic beach sand losses due to erosion from predicted future sea level rise (0.5–1.0 m), based on increasing submarine accommodation spaces in the high-wave-energy coast of the Pacific Northwest, Washington, Oregon, and Northern California, USA

The U.S. Pacific Northwest (PNW) coastline (1000 km) has been analyzed for conditions that could impact beach erosion from potential near-future (100 year) sea level rise (SLR). Heavy mineral analysis of river, beach, and shelf samples (n = 105) establish the sources of the beach deposits. River bedload discharge and intervening estuarine sinks for river sand supplies (n = 31) were normalized to the one century time interval. Twenty-six subcell beaches (657 km in combined length) were surveyed (153 profiles) for beach sand widths (20–412 m) and sand cross-sectional areas (20–1810 m2) above wave-cut platforms and/or 0 m tidal datum. Cross-sectional areas were multiplied by beach segments to yield subcell beach sand volumes (0.4 × 106 m3–35.8 × 106 m3 ± 20% uncertainty). Innermost-shelf profiles were measured for distance to the 100-year depth of closure (30 m) to digitize the areas of inner-shelf accommodation space. Both innermost-shelf and estuarine accommodation space volumes for beach sand displacements were established for 0.5 and 1.0 m SLR. The existing subcell beach sand volumes and computed new beach sand supplies (rivers and longshore transport) were subtracted from the estimated sand volumes lost to submarine accommodation spaces to establish potential beach sand deficits from near-future SLR. Of the 26 surveyed active-beaches, some 60% and 80% (by length) are predicted to be lost, respectively, from the 0.5 m and 1.0 m SLR or equivalent littoral sand sedimentation in submarine accommodation spaces. Projected losses reach 90% for all PNW beaches (~900 km total length) from 1.0 m SLR. The computed beach sand deficits are used to estimate soft-sand retreat distances or erosional beach step backs (50–590 m ± 35% uncertainty) in unrevetted barrier spit and beach/dune deflation plains from 1.0 m SLR. Such empirical accommodation space analyses should have worldwide relevance to predicting beach erosion from near-future SLR.

Remobilizing stabilized island dunes for keeping up with sea level rise?

Dune spits of the island of Sylt (North Sea) persisted through millennia by mobile dunes transferring sand from exposed to sheltered shores. However, 150 years of systematic planting on washovers, blowouts and migrant dunes have almost completely stopped this sand conveyor belt. Spits lost sand until sand replenishments to the exposed side compensated for losses during the last three decades. Based on maps since 1878, aerial images from the 1930s onward as well as botanical ground surveys, we document a long-term shift from loose grass cover to dense heather dominated vegetation. Bare sand areas almost vanished and high shrubs proliferated. Only three dunes continue migrating with about 3 m a-1 since 1936. Mainly artificial dune stabilizations and introduced plants have facilitated succession to an almost complete plant cover. Thus, revitalization of aeolian dynamics would be desirable, and pilot projects may acquire the appropriate knowledge. For a 1.7 × 2.5-km corridor across the island spit, we therefor discuss two suggested experiments: (1) intensify sand nourishments to the eroding beach and stop stabilization measures to allow excess sand blown inland and washovers entering deflation plains, and (2) examine the potential of tunnels for roads to let mobile dunes passing over. Such experiments may not only contribute to dune biodiversity but also to long-ranging adaptations of crowded barrier islands to accelerating sea level rise.

Weakening of northeast trade winds during the Heinrich stadial 1 event recorded by dune field stabilization in tropical Brazil

AbstractThe identification, characterization, and mapping of large areas of stabilized eolian features along the tropical northeastern Brazilian coast enabled recognition of the existence of one of the largest Quaternary dune fields (16,000 km2) in South America. This paleodune system is observed inland of the Lençóis Maranhenses transgressive dune field (2.5°S, 43°W) and comprises deflation plains, stabilized parabolic dunes, and barchanoid chains developed under the action of northeast (NE) trade winds. Optically stimulated luminescence ages coupled with geomorphological analysis were used to constrain the time of dune field stabilization. Ages of stabilization of parabolic dunes and barchanoid chains throughout this paleodune system range between 19 to 14 ka showing heterogeneous dune stabilization by vegetation growth during a 5 ka time interval. Dune field stabilization is related to a decrease in NE trade wind strength and increase in precipitation as a consequence of the southward shift of the Intertropical Convergence Zone during the Heinrich stadial 1 event (18–15 ka), which resulted in a lower eolian drift potential, less sand input by alongshore transport, and low sediment availability to eolian transport, due to an increase in moisture to support vegetation growth and rising relative sea level.

OS ECOSSISTEMAS DUNARES E A LEGISLAÇÃO AMBIENTAL BRASILEIRA

DOI: http://dx.doi.org/10.12957/geouerj.2013.5546 Brazil covers various ecosystems, including the dune, a complex endowed with naturalfeatures interdependent and interconnected among them, mobile and fixed dunes,deflation plains and beaches. However, the current Brazilian environmental legislationat the federal level does not seem to understand and / or consider such relevant features,in view of the Federal Law No 12.651-2012 (Forestry Code) which presents the fixeddunes as a feature separate from the others, characterizing them as PermanentPreservation Areas and other features of the dune ecosystem, no. The paper presentsscientific concepts and legal reasoning that the dunes are treated as an ecosystem andthat this is protected under federal law under this fundamental premise, under the samerisks that the alleged sectorized legal protection is compromised by forms of historicaland current use and occupation of the ecosystem in the country.

Dolomitic paleosols in the lagoonal tetrapod track-bearing succession of the Holy Cross Mountains (Middle Devonian, Poland)

The Eifelian Zachełmie succession consists of several transgressive–regressive cycles, 1 to 3m thick, starting with evenly laminated marly–shaly dolomicrites and transitioning upward into irregularly laminated dolomitic laminites with well-preserved sedimentary textures. Their upper levels are frequently mud-cracked, and they are topped by massive to nodular dolomite beds, 5 to 30cm thick, which exhibit various degrees of internal deformation. These disturbed beds were investigated in detail on the basis of saw-cut slabs, thin sections, SEM, mineralogical XRD and chemical analyses including stable oxygen and carbon isotopes. The investigations revealed a range of paleosol features, such as columnar peds, characteristically deformed surfaces (microbial earth), tubular structures interpreted as plant roots, and blackened clasts. The SEM images show that the beds are finely detrital in nature; the dolomitic silt is interpreted as having been reworked from adjacent laminated microbial muds. This interpretation is confirmed by the consistent marine stable isotope signatures of the dolomite. Slight depletion in 13C points to a minor authigenic addition related to soil CO2 input and/or microbial activity.The disturbed beds are interpreted as waterlogged paleosols showing different stages of pedogenesis related to varying durations of subaerial exposure, most likely ranging from hundreds to a few thousands of years. The paleosols developed on low-relief coastal deflation plains separating shallow lagoons fed by marine waters. The semi-arid to sub-humid seasonal climate is indicated by evaporite traces, the development of columnar peds, and the covariance of the C and O stable isotopic values.The Zachełmie disturbed beds appear to represent a unique example of dolomitic paleosols retaining the nearly marine chemical signatures of their marine-lagoonal dolomitic substrates, with little meteoric or vadose-evaporitic overprint. Their occurrence in the Zachełmie succession significantly changes our views on early tetrapod habitats, which apparently included permanently elevated and sparsely vegetated areas adjacent to shallow marine lagoons.

Conceptual models of the evolution of transgressive dune field systems

This paper examines the evolutionary paths of some transgressive dune fields that have formed on different coasts of the world, and presents some initial conceptual models of system dynamics for transgressive dune sheets and dune fields. Various evolutionary pathways are conceptualized based on a visual examination of dune fields from around the world. On coasts with high sediment supply, dune sheets and dune fields tend to accumulate as large scale barrier systems with little colonization of vegetation in arid-hyper to arid climate regimes, and as multiple, active discrete phases of dune field and deflation plain couplets in temperate to tropical environments. Active dune fields tend to be singular entities on coasts with low to moderate sediment supply. Landscape complexity and vegetation richness and diversity increases as dune fields evolve from simple active sheets and dunes to single and multiple deflation plains and basins, precipitation ridges, nebkha fields and a host of other dune types associated with vegetation (e.g. trailing ridges, slacks, remnant knobs, gegenwalle ridges and dune track ridges, ‘tree islands’ and ‘bush pockets’). Three principal scenarios of transgressive dune sheet and dune field development are discussed, including dune sheets or dune fields evolving directly from the backshore, development following foredune and/or dune field erosion, and development from the breakdown or merging of parabolic dunes. Various stages of evolution are outlined for each scenario. Knowledge of evolutionary patterns and stages in coastal dune fields is very limited and caution is urged in attempts to reverse, change and/or modify dune fields to ‘restore’ some perceived loss of ecosystem or dune functioning.

Backbeach Deflation Aprons: Morphology and Sedimentology

Backbeach deflation aprons are heterogeneous, coarse clastic deposits associated with active transverse dune fields. The apron comprises variously angular, rounded, fractured, cracked, polished, and ventifacted clasts of bedrock (local and exotic), beachrock, and bioherm fragments (coral and worm reef). Terrestrial and anthropogenic clasts (from archeological sites, deflated dunes, flotsam, and shipwrecks) are also present. The unit forms as a lag deposit on top of a gently sloping (ca. 0.008), planar sandy deflation surface and is typically only one clast thick. It is up to 100 m wide and extends for tens of kilometers along the coast. It is replaced landward by a steep (ca. 0.1) deflated soil surface armored with a layer of iron concretions. Backbeach deflation aprons are compound deposits that result from marine storm, eolian, and human activity since the mid- Holocene. The depositional model proposed involves periodic storm deposition of coarse clasts (of beachrock, bedrock, and biogenic origin) and flotsam (shipwreck and other floating debris) on the backbeach or dunes. Some clasts are deposited directly into interdune depressions and enter the deflation plain immediately. Others are deposited initially on dune surfaces. Dune migration results in winnowing of the storm-deposited coarse clasts (together with rhizoliths and any other coarse material in the dune) until they come to rest on the deflation surface. The lag deposit is subsequently buried and uncovered multiple times by dune migration, during which time it is exposed to polishing and subaerial weathering. Consequently, the lag comprises a variety of materials that reflect both storm and eolian processes. The clasts exhibit variable degrees of rounding, polishing, and ventification according to how long they have been in the deposit.Backbeach deflation aprons are characteristic of sandy beaches along approximately 475 km (. 10% of the total length) of the South African east coast. They develop in association with large-scale transverse dunefields on the backbeach, which in turn depend on reversing shore-parallel winds and high sediment abundance. The variable degree of polishing and weathering, planar surface, low elevation, and back-beach location along extensive shoreline distances distinguish backbeach deflation aprons from tsunami or marine storm deposits.

Transgressive dunefield landforms and vegetation associations, Doña Juana, Veracruz, Mexico

AbstractTransgressive dune fields often comprise a multiplicity of landforms where vegetation processes largely affect landform dynamics, which in turn, also affect vegetation processes. These associations have seldom been studied in detail. This paper examines four separate landform types in a complex coastal transgressive dunefield located in the central Gulf of Mexico, in order to assess the relationships between dunefield habitat, local environmental factors, vegetation associations and landform evolution. Topographic surveys using tape and clinometer were conducted in conjunction with vegetation survey transects at four locations across the Doña Juana dunefield. Vegetation surveys allowed the estimation of relative plant cover of each plant species found along the transects. A large variety of landforms were found at the Doña Juana Dunefield: deflation plains, gegenwalle (counter) ridges, transverse dune trailing ridges, blowouts and parabolic dunes, aklé (fish‐scale shaped) dunefields and precipitation ridges, with plant species associations developing on these different landforms equally variable. Flood tolerant species were located in the lower parts (deflation plain and gegenwalle ridges) whereas the older and dryer parts were covered by coastal matorral shrubs. Burial‐tolerant species were dominant in the most mobile areas (blowouts and aklé dunefield and margin). The dune trailing ridge, with relatively milder conditions, showed the highest richness, with no dominant species. A dual interaction was found such that colonizing species both create and affect topography, and in turn, topography determines vegetation association and succession patterns. In coastal dunes, the vegetation and abiotic environment (namely the different landforms and the inherent micronevironmental variability) interact tightly and generate a complex and highly dynamic biogeomorphic system where substrate mobility and colonization processes reinforce one another in positive feedback. Copyright © 2010 John Wiley & Sons, Ltd.

Evolution of Eureka Flat: A dust-producing engine of the Palouse loess, USA

Sedimentologic, stratigraphic, and pedologic evidence demonstrates that Eureka Flat (EF), a narrow, 80-km-long deflation plain in south-central Washington, USA, is the source for the thick and widespread loess of the Palouse region. Located in the southern Columbia Plateau, EF has been a depocenter for abundant clay-to-sand-sized sediment derived from repeated glacial outburst floods that swept through the area during the Pleistocene. Prevailing SW winds that were funneled across EF remobilized flood sediment into sand dunes, sand sheets, and loess. An eolian sand sheet buried beneath 1.8 m of loess at the downwind end of EF attests to bioclimatically driven changes in the style of eolian deposition. The depositional transition from sand sheet to loess is characterized by a change from wind-rippled strata to structureless, bimodal sand and silt with insect burrows and rhizoliths, to unimodal sandy loess. Soil moisture and density of dust-trapping vegetation control where sand dunes and loess accumulate. Up to 4.5 m of post-LGM loess mantles the landscape adjacent to and downwind from EF. Some of the thickest loess deposits owe their origins to the sequestering of eolian sand particles by topographic traps such as the Touchet River and its tributary valleys. The removal of saltating sand from the eolian system promotes thick accumulation of loess downwind of topographic traps. Patterns of loess accumulation across the Columbia Plateau are identified on isopach maps of major pre- and post-LGM loess units and show that EF has been the major engine for the production of atmospheric dust and loess during both times.

The role of wind and splash erosion in inland drift-sand areas in the Netherlands

European drift-sand areas reached their maximum size in the 19th century. From the late 19th until the mid-20th century most drift-sand areas in Europe were successfully reforested. Today drift-sand formation can still be studied in the Netherlands. However, due to change in land-use, their limited size, eutrophication and colonisation by invasive exotics, the area occupied by active drift sand is rapidly declining and with it its unique fauna and vegetation. Between 2001 and 2005, experiments and observations were carried out at the inland drift-sand area Kootwijkerzand (central Netherlands) to know more about the extent, the intensity and the role of wind and splash erosion in a drift-sand ecosystem. Measurements were carried out on the horizontal sediment flux, the vertical accumulation flux, the raising and lowering of the surface, the organic matter content of the topsoil, the saltation activity and the weather conditions. An attempt was also made to evaluate the effect of various measures to re-activate erosion. Without sufficient erosion the scattered drift-sand vegetation will rapidly change into closed, grass-dominated vegetation. The role of erosion in the drift-sand ecosystem is therefore crucial: erosion slows down the succession rate because it causes the regular deposition of nutrient-poor sediment, and facilitates the regular renewal of the vegetation by creating new locations with extremely poor conditions for colonisation (blow-outs). On bare deflation plains wind erosion is the dominant process. Here the transport generated by splash drift can be of the same magnitude as during a moderate wind erosion event, but splash drift events are less frequent and also shorter than wind erosion events. They normally represent less than 10% of the total sediment transport. In the scattered drift-sand vegetation areas, on the other hand, splash erosion and splash drift dominate. Here the organic matter content of the transported (and later deposited) sediment is equal to the organic matter content of the parent soil, showing that splash (drift) has been the main transport mechanism. Biological crusts developed in these areas may later reduce the influence of splash. High transport rates are needed to reactivate wind erosion in vegetated areas. Under the present conditions the erosion activity in most drift-sand areas is small. Heavy wind erosion is only observed during extreme storms.

Morphology of the Itapeva to Tramandai transgressive dunefield barrier system and mid‐ to late Holocene sea level change

AbstractThe surface morphology of the transgressive dunefield barrier extending from Itapeva to Tramandai along the northern littoral of Rio Grande do Sul, is examined and an attempt is presented to link morphological changes across the barrier to Holocene sea level changes. The 4·5 km wide Holocene barrier displays two typical morphologies: an inner part dominated by large‐scale, continuous alongshore, overlapping dunefield phases comprising sand sheets, dunes, deflation plains and precipitation ridges; and an outer part dominated by discontinuous, medium‐ to small‐scale, triangular to lobate transgressive dunefield phases, cut by both active and relict (palaeo‐) creeks or washouts. Holocene sea level in the region rose to c. +1 to +3 m above present reaching a maximum around 5100 years bp and then progressively fell to the present level. We argue that the effect on barrier development was to suppress the development of a drainage system during the rising and maximum stages, and encourage the development of an organized drainage system in the form of regularly spaced washouts during the falling period, and that this change in sea level from rising to falling therefore produced the large‐scale differences in barrier morphology. Copyright © 2006 John Wiley & Sons, Ltd.

Beach ridges, foredunes or transgressive dunefields? Definitions and an examination of the Torres to Tramandaí barrier system, Southern Brazil

Many prograded barriers and some dunefields in theworld have been termed 'beach ridge' plains, but the actual genesis of the 'ridges' is often unknown. Use of the terms, berms, beach ridges and foredunes is also confusing in the literature because their definitions are highly variable and are commonly used interchangeably. Thus, the formation and definition of sand berms, beach ridges and foredunes is briefly reviewed. Beach ridges are re-defined as entirely wave formed deposits which are most commonly formed during high wave conditions and/or elevated water levels (e.g. storm surges). Foredunes are formed by aeolian sand deposition in vegetation on the backshore. Some dunefields in Brazil have been called beach ridge plains when they are, in fact, foredune plains, transgressive dunefields, or complex barriers (i.e. barriers comprising two types of dunes). The Holocene barrier extending from Torres to Tramandaí in southern Brazil has been regarded as a beach ridge plain. The landforms of this Holocene barrier comprise wide, relatively linear, widely spaced (400-600m), shore parallel ridges on the landward half, and more closely spaced (80-400m), lobate and crescentic, discrete ridges on the seaward half. Low, rolling dunefields, sand sheets, nebkha fields and deflation plains occur between the ridges. The barrier is re-interpreted as a prograded, transgressive dunefield barrier.

Evolution of a dune from crescentic to parabolic form in response to short-term climatic changes: Råbjerg Mile, Skagen Odde, Denmark

Råbjerg Mile, a complex parabolic dune, reaches a height of 20 m above the deflation plain. The width of the dune is 900 m and the length of the whole dune is 1500 m. The dune is covered by 0.5–1.5 m high transverse dune ridges. The dune has migrated approximately 1 km since 1887 A.D., accompanied by a change in the migration direction from ESE (100°) to ENE (68°). The morphology of Råbjerg Mile through the last 100 years is illustrated by a geographical information system (Arc/Info) applied to a series of high-quality topographical maps. Based on the digitized contour lines, the evolution of Råbjerg Mile can be followed from an initial crescentic form in 1887 A.D. to a complex parabolic dune in this century. Dune dynamics and sites of erosion and deposition are evaluated from the digital terrain models. Changes in vegetation cover, documented from the maps and air photos, indicate that vegetation in the study area steadily increased with time. Calculations of resultant drift directions and gross bedform-normal transport are based on climatic data from the Skagen changed from an almost perfect transverse bedform (1887–1924) to an oblique imperfectly transverse bedform (1966 to present). The bedform alignment followed the gross bedform-normal transport rule in most years. The evolution of a parabolic dune after 1924 is related to a period of reduced wind energy and increased vegetation cover. This parabolic dune was maintained after 1960 when wind energy increased and the wind regime was more complex. At the same time the dune became markedly asymmetric because of the frequent occurrence of strong southerly and easterly winds.

Above and belowground community development in a marine sand dune ecosystem

Transects across undisturbed marine sand dunes sequentially traversed the following plant communities: littoral, foredunes, intradune complex of ridges and hollows, deflation plain, myrtle forest, and mature conifer forest. Organic carbon levels were low in the littoral zone and increased across the dune ecosystem landward to the forest communities. The highest percentage of nutrients was isolated from the heavy fraction of soil residues. Soil microfloral populations responded to vegetation, physical dune characteristics, and seasonal moisture patterns. Populations of bacteria and actinomycetes were higher in winter than during summer sampling periods in all communities. Populations of microscopic fungi were higher in winter in all the communities except the hollows. The distribution of vesicular-arbuscular mycorrhizal fungi responded to vegetation and sand dune succession but did not display seasonality. Species of Gigaspora and Acaulospora were the most commonly isolated VAM fungi.

Predicting depth to the water table based on species presence on an Oregon coast deflation plain

Vegetation on an Oregon coast deflation plain was related to changes in depth to the water table and time since the initiation of succession. A new method was evaluated for the prediction of water-table depth based on species presence or absence. It was found that for 96% of the quadrats, water-table depth was predicted to within 10 cm; for 73% of the quadrats it was predicted to within 5 cm. The method can be applied to other studies for predicting the value of environmental variables based on species presence.

RØMØ: NATURVURDERING PÅ GEOGRAFISK-ØKOLOGISK BASIS

SUMMARY Presentation of 3 maps concerning the island of Rømø: Plate 1: The landscape elements (ecotypes). Plate 2: The man-made constructions as settlements, roads, dam, dikes and a harbour as well as plantations. Plate 3: A land use map supplemented by noise zoning of road traffic, an interference leaving a minor part of the area as being untouched nature. Plate 1: 1) Tidal flats, low lying, 2) Creek, 3) Channel, 4) Tidal inlet, 5) Tidal flat, sandy, 6) High sand, 7) Sandy salt marsh, 8) beach ridge, 9) Break-through of the sea, 10) Deflation plain, 11) Dunes, minor forms, 12) Dunes, greater forms, 13) Salt marsh of the foreland, 14) Muddy tidal flats, 15) Phragmites salt marsh, 16) Agricultural area, 17) Polder area, 18) Marine foreland, dike burst. Plate 2: 1) Macadam main road, 2) Macadam road, 3) Gravel road, 4) Earth road, 5) Sand road, 6) Dike, 7) Line of poles, 8) Settlements, 9) Recreational area, 10) Camping, 11) Plantations. Plate 3: 12) Agricultural area, diked in, 13) Agricultural area, undiked. Principles of nature conservancy as well as the future problems of agriculture on the island are discussed.