Great Sand Dunes National Monument Research Articles

First Report of White Pine Blister Rust on Rocky Mountain Bristlecone Pine.

White pine blister rust caused by Cronartium ribicola was introduced into North America in the early 20th century and is spreading throughout the range of five-needle pines. In northern Colorado, this pathogen was first observed in 1998 on limber pine (Pinus flexilis) (1). It has not been reported on Rocky Mountain or Great Basin bristlecone pine (Pinus aristata and P. longaeva, respectively) in nature. However, Rocky Mountain bristlecone pine is susceptible to the disease when artificially inoculated (2). In October 2003, a Rocky Mountain bristlecone pine was found infected with C. ribicola in the Great Sand Dunes National Monument, Alamosa County, Colorado. Seven branch cankers were observed on the tree. Cankers ranged in length from 15 to 41 cm and were estimated to be approximately 5 to 7 years old. Distinct C. ribicola branch symptoms were observed, including flagging, spindle-shaped swellings, and 6 mm long aecial scars. A branch was deposited at the Colorado State Herbarium. Microscopic examination of spores within remnant aecial blisters revealed aeciospores characteristic of C. ribicola (yellow-orange, ellipsoid, verrucose, and 19 × 25 μm). Cankers were only observed on one bristlecone pine. However, most limber pines in the area were infected with C. ribicola, including a limber pine less than 1 m from the infected bristlecone pine. To our knowledge, this is the first report that shows Rocky Mountain bristlecone pine can become infected naturally, and the pathogen is further south in Colorado on limber pine than previously reported. These observations suggest the need for a more complete investigation of this disease on bristlecone pines.

Stream/aquifer interactions at Great Sand Dunes National Monument, Colorado: influences on interdunal wetland disappearance

Between 1937 and 1995 a complex of more than 100 interdunal wetlands disappeared from Great Sand Dunes National Monument, Colorado. We investigated three hypotheses that could explain wetland disappearance: (1) dune movement during a severe drought in the 1950s buried the wetlands, (2) agriculture related ground water pumping lowered the regional water table, and (3) changes in local hydrologic processes led to wetland loss. We used regional stream flow records, ground water level measurements, natural stable isotope analyses, soil stratigraphy, buried seed banks, and ground water modeling to address these hypotheses. Hydrologic data and stable isotope analyses illustrated the interaction between Sand Creek, a nearby stream, and the unconfined aquifer in the area where wetlands occurred. When the intermittent Sand Creek flows, seepage through its bed creates a large ground water mound under the creek. The seasonal development and dispersion of this mound propagates pressure waves through the aquifer that influence ground water levels up to 2 km from Sand Creek. Our data suggest the primary factors contributing to wetland disappearance were recent climatic fluctuations and incision of the Sand Creek channel. Below average stream flow between 1950 and 1980 reduced the duration of Sand Creek flow across the dune complex, minimizing ground water mound development. Consequently, the water table in the unconfined aquifer dropped ∼1.0 m and interdunal wetlands dried up. Twentieth Century incision of Sand Creek's channel reduced ground water mound height ∼2.5 m, decreasing seasonal water table fluctuations at interdunal wetlands and contributing to the overall water table decline. Long-term wet and dry cycles affect the water table elevation more than channel incision, leading us to conclude that many interdunal wetlands are ephemeral features. Wetland area is maximized during consecutive years of above average Sand Creek discharge and minimized as the water table drops during dry periods.

An analysis of the current stability of the Dune Field at Great Sand Dunes National Monument using temporal TM imagery (1984–1998)

Research conducted at the Great Sand Dunes National Monument (37°46.5′N, 105°32.5′W) thus far has focused on dune composition in order to explain formation, dune migration to monitor aeolian processes, and dune extent to detect encroachment in the eastern periphery, a region that contains several visitor services. These studies used a series of field techniques in conjunction with aerial photography; however, modern satellite data, such as temporal TM imagery, were not used to track changes of the dunes. In this study, I used two TM images from 1984 and 1998 to examine changes in dune extent. A series of image enhancements, including edge enhancements were applied, and a supervised classification was conducted. Overall classification accuracies, based on ground truth data, ranged from 89% (1998) to 91% (1984). Over the study period, the amount of sand in the entire complex decreased in area by 416.4 ha, dune grass decreased by 487.5 ha, and a semidesert scrub category containing a mixture of bushes, taller grasses, and desert pavement increased by 1457.3 ha. Few changes in the extent and orientation of the main dune complex were observed; however, notable changes were observed in the periphery. On the western side of the complex, dune grass is slowly being converted to scrub; as a result, the extent of exposed sand is decreasing. On the eastern side, dune grass and scrub are increasing, succeeding upon the dunes. These results demonstrate the stability of the main dune complex and suggest that dune migration in the periphery is no longer a concern.

Using GPS to Teach More Than Accurate Positions

Undergraduate science majors need practice in critical thinking, quantitative analysis, and judging whether their calculated answers are physically reasonable. We have developed exercises using handheld GPS receivers that expose students to this recent technology and promote larger goals that transcend the simple use of a tool for precision location. Using the GPS to calculate the volume of sand in the dunes at Great Sand Dunes National Monument in Colorado requires traversing the dunes, plotting a topographic profile, calculating the volume of sand traversed, and then extrapolating to estimate the volume in the entire dune field. This exercise serves to reinforce students' abilities to think quantitatively, to make realistic “back of the envelope” assumptions, and to determine whether their final answers make physical sense. Using the GPS to measure the running track at an outdoor track and field stadium requires students to gather data, import the data into a spreadsheet such as Microsoft Excel, plot it and perform an error assessment. This exercise reinforces concepts from statistics, and allows students to estimate the precision of GPS measurements both quantitatively and qualitatively. Together these two exercises promote quantitative analysis in a geologic context.

The relationship between the water table and the surface flow of a losing stream, lower Medano Creek, Great Sand Dunes National Monument, Colorado

Proposed groundwater withdrawals in the San Luis Valley of Colorado may lower the water table in Great Sand Dunes National Monument. In response, the National Park Service initiated a study that has produced a generalized conceptual model of the hydrologic system in order to assess whether a lowering of the water table might decrease the surface flow of lower Medano Creek. Based upon information obtained during the drilling of several boreholes, there appear to be five important hydrostratigraphic units underlying lower Medano Creek within the upper 30 m of the ground surface: 1. a perched aquifer overlying an aquitard located between about 5 and 6 m below the ground surface; 2. the aquitard itself; 3. an unconfined aquifer located between the upper and lower aquitards; 4. an aquitard located between about 27 and 29 m below the ground surface; and 5. a confined underlying the lower aquitard. Because the areal extent of the aquitards cannot be determined from the borehole data, a detailed conceptual model of the hydrogeologic system underlying lower Medano Creek cannot be developed. However, a generalized conceptual model can be envisioned that consists of a complex system of interlayered aquifers and leaky aquitards, with each aquifer having a unique hydraulic head. Water levels in the perched aquifer rise rapidly to their annual maximum levels in response to the arrival of the flow terminus of Medano Creek during the spring runoff event, and the location of the flow terminus is directly dependent upon the discharge of the creek. Water levels in the deeper, non-perched aquifers do not appear to fluctuate significantly in response to the arrival of the flow terminus, demonstrating that it is unlikely that the proposed groundwater withdrawals will decrease the surface flow of lower Medano Creek.

Surface Flow on Medano, Mosca, and Sand Creeks in Relation to Fault Zones and Water Tables

This project seeks to determine the relation between surging surface flow and projected groundwater declines at the Great Sand Dunes National Monument. Surging flow in Medano Creek is a unique visitor attraction at the Monument, and is exhibited from April through July at easily accessible sites. Projected water table declines of up to 46 m due to an adjacent groundwater development scheme may increase infiltration rates in Monument creeks, thus leading to diminished or eliminated surge flow. This report covers the third 6-month period of the contract (May 15-Nov. 15, 1992).

Great Sand Dunes National Monument Vegetation Patterns

This project is designed to chacterize and map the vegetation of the Great Sand Dunes National Monument, Colorado (GSDNM) and to determine if the vegetated areas in the dune field are permanent, temporary, or migratory. It is not known if the vegetation around the dunes is encroaching on the dunes, being replaced by the dunes or is stable. There are also concerns about the possible effect a proposed water export project adjacent to GSDNM would have on the dunes and their vegetation.

Surface Flow on Medano, Mosca, and Sand Creeks in Relation to Fault Zones and Water Tables

This research seeks to determine the relation between surging surface flow and projected groundwater declines at the Great Sand Dunes National Monument. Surging flow in Medano Creek is a unique visitor attraction at the Monument, and is exhibited from April through July at easily accessible sites. Projected water table declines of up to 46 m due to an adjacent groundwater development scheme may increase infiltration rates in Monument creeks, thus leading to diminished or eliminated surge flow.

Fluvial‐aeolian interactions: Part I, modern systems

ABSTRACTTwo modern fluvial‐aeolian depositional systems (Great Sand Dunes National Monument, Colorado and the Mojave River Wash, California) are remarkably similar in spite of different climates, sizes, fluvial sediment textures, and relative directions of aeolian and fluvial transport. Dune growth and migration, and deflation of blowouts create 8–10 m of local relief in unflooded aeolian landscapes.There are six prominent fluvial‐aeolian interactions. (1) Fluvial flow extends into the aeolian system until it is dammed by aeolian landforms; (2) interdune areas (overbank‐interdunes) upstream of aeolian dams, and alongside channels are flooded; (3) water erodes dunes alongside channels and interdunes; (4) flood waters deposit sediment in interdune areas; (5) fluvially derived groundwater floods interdunes (interdune‐playas); (6) wind erodes fluvial sediment and redeposits it in the aeolian system.Unique and characteristic sediments are deposited in overbank‐interdunes and in interdune‐playas, reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions. These fluvial‐aeolian interdune deposits are characterized by irregular, concave‐up bases and flat upper surfaces containing mudcracks or evaporite cement.Characteristic low‐relief surfaces form in aeolian systems as an effect of flooding. Fluvial deposits are resistant to aeolian deflation. Aeolian sand is preserved when flood sediments are deposited around the bases of the dunes. Thus repetitive fluvial and aeolian aggradation tends to be ‘stepwise’ as interdune floors are suddenly raised during floods. The effects of flooding should be easy to recognize in ancient aeolianites, even beyond the area covered with overbank muds.

Impact of Early Diagenesis of Eolian Reservoirs, Great Sand Dunes National Monument, Colorado: ABSTRACT

Dune and associated alluvial and playa deposits at Great Sand Dunes National Monument, Colorado, provide an excellent opportunity to study early diagenetic development of vertical and horizontal permeability barriers in recent eolian deposits (> 10 ka). Cements observed include calcite, aragonite, protodolomite(?), amorphous silica, iron hydroxide, smectite, trona, and halite. Cementation is controlled by the availability of water, with several hydrologic subenvironments producing different cements. Evaporative cementation in dunes adjacent to playas is commonly dominated by trona and halite, but calcite, aragonite, and amorphous silica also bind the sediment. These cements are generally most concentrated in fine laminations where capillary action has pulled water into dunes. Iron hydroxides, calcite, and amorphous silica precipitate at the interface between ground water and streams or lakes, where the pH gradient may exceed 5 pH units (pH 5.7-11.5). Subsequent movement of the ground-water table can result in cross-cutting cement zones. Early cementation in dunes prevents deflation and provides a mechanism for preservation of the reservoir unit. Intense cementation may permanently occlude porosity, or leaching may reestablish well-interconnected porosity. An understanding of the extent and composition of early cement zones can be used to improve hydrodynamic models for production and enhanced recovery. End_of_Article - Last_Page 276------------

Bed‐form‐dependent pulsating flow in medano creek, southern colorado

AbstractSome sand‐bed streams exhibit unsteady supercritical flow in the form of periodic bores that propagate downstream. The bores are formed by unstable antidunes, which store water while growing in amplitude and then release the stored water, when the antidunes wash out to form a plane bed. A cyclic process of antidune growth, oversteepening, antidune breaking, then bed‐form washout produced bores on regular periodic intervals of roughly 15 s in Medano Creek, Great Sand Dunes National Monument, Colorado. This periodic bore‐generating pulsating flow, is bed‐form dependent, and it requires sufficiently high flow velocities and sediment transport rates to form unstable breaking antidunes. The Froude number maximum is 1.8, below that required for slug flow.Pulsating flow has been observed in flumes, arroyos, and rivers, and it may be more common than initially anticipated. Its high erosive capacity can influence both channel morphology and the character of associated sedimentary deposits.

Origin, sedimentary features, and significance of low-angle eolian "sand sheet" deposits, Great Sand Dunes National Monument and vicinity, Colorado

Low-angle eolian deposits of a sand sheet constitute an areally extensive (710 km 2 ), transitional facies between high-angle eolian dunes and non-eolian deposits near Great Sand Dunes National Monument, Colorado. The bulk of the low-angle eolian deposits of the sand sheet lie in a 15-km-wide belt between the main dune mass at Great Sand Dunes and the Rio Grande River 45 km to the southeast, or upwind. These low-angle eolian deposits have a number of distinctive sedimentary features which are useful in interpreting ancient rocks, including: (1) coarse-grained, high-index ripples (commonly horizontal); (2) gently dipping, curved or irregular surfaces of erosion (several meters in length) within the deposits; (3) abundant bioturbation traces, formed mainly by insects and plant roots; (4) patches or zones (extending up to 1 m below the ground surface) of bioturbated sand resulting from destruction of laminae by grass root growth; (5) convex upward laminations; (6) small scale cut-and-fill structures, perhaps due to scour around plant roots and subsequent infill; (7) gently dipping, poorly laminated layers resulting from adjacent grainfall deposition; (8) sets of normal- and inverse-graded laminae 1- to 4-mm-thick; (9) discontinuous thin 1- to 4-mm-thick layers of coarse sand intercalated with fine sand; (10) intercalation of non-eolian materials, including silty pond sediment and gravelly stream deposits; (11) occasional intercalation of high-angle eolian deposits. Low-angle eolian deposits of the sand sheet originate mainly by gentle deceleration of wind, in the lee of small topographic features, which produces a different style of deposition compared to the more extreme flow separation at the brink of a dune slipface. Low to moderate velocities, typical of those observed during this study, generally remove fine sand from exposed areas, and deposit the sand in nearby topographically lower or sheltered places, resulting in more texturally homogeneous sets of laminae (type a) overlying more texturally heterogeneous deposits (type b). Recognition of low-angle eolian deposits may assist in identification of margins of ancient dune fields. From an economic point of view such information may be of value in predicting either (a) stratigraphic continuity of high-angle eolian reservoir rock, or (b) proximity of high-angle eolian rock.

Discriminant Analysis Versus Factor Analysis of Grain-Size Data from Different Environments and Sedimentary Structures: ABSTRACT

Grain-size data analyzed by multivariate computer techniques allows (1) discrimination of environment of deposition and (2) recognition of sedimentary structures. Multiple discriminant analysis where used in conjunction with variables derived from ¼-phi-sieve grain-size analysis was found to be the most useful multivariate technique. Grain-size samples from 3 environments (Arkansas River, Great Sand Dunes National Monument, Colorado, and Gulf Coast beaches) were used as environments in discriminant analysis. With the intention of classifying 49 samples from Bijou Creek, Colorado, they were listed in the discriminant analysis program as unknowns. Thirty-six of 39 unknowns were correctly classified by the program as river sediments. Q/mode factor analysis correctly classified 32 of the Bijou Creek samples with known river samples. Variations in grain-size distributions within a given environment were studied in an Arkansas River sand wave. Foreset beds, climbing ripples, and horizontal laminations were designated as sedimentary structures. By use of multiple discriminant analysis 20 of 21 samples from a second sand wave were classified correctly. Using Q-mode factor analysis all but 3 samples were classified correctly. By analyzing separately each of the 2 or 3 populations appearing as straight lines on cumulative plots on normal probability paper, greater discrimination between environments was obtained than by using standard grain-size parameters calculated by assuming each sample represented a single population. End_of_Article - Last_Page 873------------