Active Sand Dunes Research Articles

Pluvial Lake Basins of West Texas

Deep linear lake basins in West Texas originated by "cap rock" breaching along Pleistocene pluvial streams, but large shallow circular lake basins were caused mainly by "cap rock" breaching due to solution and leaching in blowouts. Large pluvial lake basins and associated playas oriented normal to ancient prevailing winds developed by end-current erosion during wet periods, but the small post-Wisconsin lake basins which now pockmark the plains, as well as the present playas of the larger pluvial basins, developed by wind deflation mainly during the arid Altithermal period 6,500 to 5,000 years B.P. Isolated examples of small basins formed by meteorite impact, animals, infiltration, and active sand dunes also exist. Small basins formed by differential subsidence and piping and roofing are unknown but may occur. Radiocarbon dates, sedimentation rates, and paleoclimatic studies indicate the basins have received little fill since the last pluvial period. Beneath thin Recent playa surface deposits is a thin zone of Wisconsin Tahoka Clay resting on a variable thickness of pre-Tahoka (pre-Wisconsin?) lacustrine strata. The large pluvial lake basins antedate approximately 27,000-year-old sediments, and the present playas postdate approximately 17,000-year-old strata.

Plant Succession on Dune Sands in Fremont County, Idaho

Active sand dunes in Fremont County, Idaho, move northeastward at an approximate rate of 3 m/year. Sand deposits, continuous in some areas for several kilometers, extend to windward from the dunes in the form of long ridges, parallel to the wind direction. Five successional vegetation stages, distinct as to dominant species, appear on the deposits as belts transverse to the direction of dune movement. Elymus flavascens and Psoralea lanceolata dominate the pioneer stage, which lasts up to about 30 years. The second stage, dominated by Chrysothamnus nauseosus with an understory of the two pioneer species, lasts from 10 to 70 years. Purshia tridentata then replaces much of the C. nauseosus to form a third stage lasting for about 50 to 70 years. Dominant species in the fourth stage are Artemisia tridentata, P. tridentata, and in many areas Prunus virginiana var. demissa. Very little A. tridentata is found after 700 to 900 years of stabilization, and the final and most extensive stage on deep sand is dominated by dense P. tridentata with clumps of P. virginiana var. demissa. Vegetation on old, shallow deposits has characteristics of both that on deep sand and the Artemisia/bunchgrass type on the surrounding native soil. Fields that were plowed and abandoned in the early 1930's now support dense stands of Stipa comata. The presence of dense shrub stands on dunes now topographically sheltered by the wind, but not on migrating dunes, indicates that establishment of a species on sand depends on relative site stability rather than on soil nutrient buildup caused by previous vegetation. Deep sand holds moisture available to plants throughout the dry part of the growing season while the native soil does not, which probably accounts for the greater shrub density and vigor on sand.

A New Species of Glenanthe Haliday (Diptera: Ephydridae) from the North American Interior

One of the most unusual results of intensive collecting in southern Manitoba in. 1958 was the discovery of this striking representative of a dominantly coastal genus of Ephydridae. It ivas collected at several times but in only the one locality, the Bald Head Hills, a region of active sand dunes in the largely stabilized, spruce-covered area representing the shores of the Pleistocene Lake Agassiz. The species is strikingly different from other species of the genus in its thoracic and wing pattern, hut in structural characters it is fairly typical.

A Tentative Classification of Sand Dunes Its Application to Dune History in the Southern High Plains

Part I. Existing sand dunes fall naturally into two groups-complex and simple, the former being much the more common. Variable factors, such as wind direction, depth of sand, irregularity of vegetal growth, etc., are responsible for the rarity of the simple dunes. It is only by first studying simple forms, however, that one can discern the origin and history of surfaces of complex form. Following is a basic classification of simple dunes which is at the same time genetic and naturalistic. It is based on the assumption that the sand-moving wind blows with unvarying direction. Simple Dunes A. Bare Surfaces or Loose Sand I. The barcan dune. An isolated bare-sand hill on a nonsandy base II. The transverse dune series. Formed on bare, loose sand of "unlimited" surface area and "unlimited" depth III. The isolated transverse dune ridge. Formed (frequently with human aid) from bare, loose sand of unlimited surface area, but shallow depth IV. Lee dunes 1. Wind-shadow dunes ("umbracer" dunes). Longitudinal dunes. Formed from a continuing (unlimited) sand supply in the lee of a bedrock obstacle 2. Shrub-coppice dunes (see p. 124) 3. Source-bordering lee dunes ("umbrafon" dunes, lee-source dunes). Formed from a continuing (unlimited) sand supply leeward from a source of sand of limited area (e.g., stream flood plain) B. Formed by Wind in Conflict with Vegetation I. Shrub-coppice dune cluster. Formed in and to leeward from bunch or clump vegetation, such as mesquite bush, on an unlimited and smooth surface of very shallow sand II. (a) Blowout or parabolic dunes; (b) elongate-blowout dunes; and (c) windrift dunes. Formed by gentle, moderate, and strong winds, respectively, on deep sand with shrub- or grass-covered surface Under the heading "Complex Dune Forms" is considered the ideal simple case of two equally effective sand-moving winds blowing at right angles. It is pointed out that even this degree of complexity is much simpler than that of many of the well-known sand-dune areas. PART II. A study of dunes in the southern High Plains by means of vertical aerial photographs reveals: 1. Up to the decade from 1920 to 1930, active sand dunes were insignificant in number and total area, compared to the anchored dunes of Recent or post-Pleistocene age. 2. There has been a systematic shift in the direction of the prevailing sand-moving wind during the last 15,000 years (estimate), such that winds which formerly blew toward S. 70° E. have been replaced gradually by modern winds blowing N. 20° E. in most of the region. For convenience in description these dunes are divided into three series: I, II, and III, from youngest to oldest. 3. An unusual series of large parallel windrift dunes, indicating strong persistent winds, was formed around 15,000 years ago. Sand dunes of this type (Series III) are apparently not forming at present to any noteworthy degree, either in the interior of North America or along the coasts.

Annual Rings of Thuja occidentalis in Relation to Climatic Conditions and Movement of Sand

1. Climatic conditions in Michigan sand dunes are sufficiently variable to produce marked effects in the annual growth of Thuja occidentalis. 2. A graph showing the annual growth of each of a group of trees indicates the period of existence of the dead trees. 3. The time required for the destruction of this particular area was approximately 160 years. 4. The active sand dune in this region averaged 3.12 feet per year in its progression into the living forest. About 20 years is required for the life of a tree to be terminated by sand moving at this rate. 5. The destruction of living forests by the moving sand in this dune region occurs very slowly, as revealed by the records of the annual growth of Thuja occidentalis.