Gravel Cover Research Articles

Effect of wave exposure on vegetation abundance, richness and depth distribution of shallow water plants in a New Zealand lake

SUMMARY 1. The effects of physical disturbance in terms of wave exposure, shore slope and substrate mobility on the presence, species richness, cover and depth limits of the low‐growing, shallow water macrophyte community (called the low mixed community) were examined at 41 shore sites in Lake Wanaka, South Island, New Zealand.2. Wave exposure at a site was described by the previous year's maximum depth of sediment motion and maximum vertical extension of waves, determined from a computer wave model. Shore slope at each site was recorded from −1 to 0 m depth, and sediment stability was assessed as the cover of small gravel.3. The low mixed community was only present on sites where the previous year's maximum depth of sediment motion was <8 m, maximum wave run‐up was <0.3 m, shore slope <0.12 m m−1, and small gravel cover <78%.4. Species richness, cover and depth limits of the low mixed community decreased with increasing disturbance on the sites. Sixty‐two percentage of the variation in species richness could be explained by physical disturbance variables when all sites were included (N=41). When only sites with a low mixed community were included (N=22), only 18% of the variation was explained. Species richness within sites supporting a low mixed community is thus poorly explained by physical disturbance, whereas presence or absence is better explained. There was no evidence to support the intermediate disturbance hypothesis in this study.5. Disturbance as a result of waves explained 86% of the variation in cover among sites with a low mixed community and accounted for 68 and 58% of the variation in upper and lower depth limit of the low mixed community, respectively.6. The models obtained in this study can be used as predictive models for the low mixed community in New Zealand lakes in relation to natural physical disturbance on the shore. By integrating these results with previous studies on the effect of water level fluctuation, we describe a generalised optimum physical habitat for the low mixed community in New Zealand lakes.

Soil erosion as affected by shrub encroachment in northeastern Patagonia

Soil erosion is the primary cause of irreversible loss of soil productivity on most rangelands. In northeastern Patagonia, the increase in soil erosion has been closely associated with the increase in shrub cover in the grass or shrub-grass steppes. We used rainfall simulation to compare infiltration and sediment production from patches of grass, shrub-grass, and shrub steppes of the Punta Ninfas range site. Bare soil and gravel covers were higher and litter cover was lower in the shrub steppe than in the shrub-grass and the grass steppes. In the shrub inter-spaces of the shrub steppe, bulk density was greater and macroporosity and soil organic matter were lower (P less than or equal to 0.05) than in the mounds beneath shrubs and in the grass and shrub-grass areas. Infiltration rate was 60 to 65% lower in the shrub steppe than in the grass and shrub-grass steppes, respectively. On the contrary, total sediment production and concentration were higher (P less than or equal to 0.05) in the shrub steppe as compared to the grass and the shrub-grass areas. Gravel cover was the variable that best predicted infiltration and sediment production. The organic matter content of the sediment, mostly litter, in the shrub and the shrub-grass steppes were similar and greater (P less than or equal to 0.05) than in the grass steppe. Runoff litter removal may represent one of the processes that drive the transition from shrub-grass to shrub steppes. High rates of sediment removal, mainly litter, from the shrub interspaces of the shrub steppe may limit the natural recovery of the soil physical and hydrological properties. These degraded patches fail to capture incident rainfall and restrict the possibilities for the recovery of perennial grasses favoring the dominance of shrubs.

Soil Erosion as Affected by Shrub Encroachment in Northeastern Patagonia

Soil erosion is the primary cause of irreversible loss of soil productivity on most rangelands. In northeastern Patagonia, the increase in soil erosion has been closely associated with the increase in shrub cover in the grass or shrub-grass steppes. We used rainfall simulation to compare infiltration and sediment production from patches of grass, shrub-grass, and shrub steppes of the Punta Ninfas range site. Bare soil and gravel covers were higher and litter cover was lower in the shrub steppe than in the shrub-grass and the grass steppes. In the shrub inter-spaces of the shrub steppe, bulk density was greater and macroporosity and soil organic matter were lower (P less than or equal to 0.05) than in the mounds beneath shrubs and in the grass and shrub-grass areas. Infiltration rate was 60 to 65% lower in the shrub steppe than in the grass and shrub-grass steppes, respectively. On the contrary, total sediment production and concentration were higher (P less than or equal to 0.05) in the shrub steppe as compared to the grass and the shrub-grass areas. Gravel cover was the variable that best predicted infiltration and sediment production. The organic matter content of the sediment, mostly litter, in the shrub and the shrub-grass steppes were similar and greater (P less than or equal to 0.05) than in the grass steppe. Runoff litter removal may represent one of the processes that drive the transition from shrub-grass to shrub steppes. High rates of sediment removal, mainly litter, from the shrub interspaces of the shrub steppe may limit the natural recovery of the soil physical and hydrological properties. These degraded patches fail to capture incident rainfall and restrict the possibilities for the recovery of perennial grasses favoring the dominance of shrubs. DOI:10.2458/azu_jrm_v55i1_parizek

Hydraulic performance of geosynthetic clay liners under gravel cover soils

Hydraulic performance of adhesive-bonded and needle-punched geotextile-supported geosynthetic clay liners (GCLs) was measured for specimens covered with uniformly graded fine, medium, and coarse gravel using flexible-wall permeameters. Local measurements of specimen thickness, water content, and mass per unit area were taken after each test to quantify thickness variability and bentonite migration/consolidation behavior. Control tests were also performed to measure GCL hydraulic performance under conventional testing conditions. Test results showed that the hydraulic performance of control and gravel-covered specimens of both GCL products improved with increasing confining stress. In addition, measured values of hydraulic conductivity for the gravel-covered specimens were less than the manufacturer's specification. The amount of bentonite migration generally increased with increasing cover soil particle size and rate of loading. Thickness variability and bentonite migration were generally less for the needle-punched product, which is attributed to the additional confinement provided by the reinforcement. The placement of an additional non-woven geotextile over the adhesive-bonded GCL was somewhat effective in reducing thickness variability and bentonite migration under rapid loading conditions.

Numerical simulation of submarine pipelines in dynamic contact with a moving seabed

The dynamic response of submarine pipelines to earthquake-generated vertical seabed motions is examined with the aid of a finite element model. A relaxation algorithm is adopted in order to overcome the problem of unknown dynamic seabed reaction forces. Rotational rigidity is assumed at the boundary points, which are allowed to move vertically in unison with the random seabed oscillations. For the interior nodes, the description of the kinetic energy loss, resulting from pipeline-seabed impact, is approached through the use of a restitution coefficient of 0.5, which represents an intermediate collision mode between a perfectly elastic and an inelastic one. Fundamental system frequencies are determined by the use of support positions obtained from a static analysis of the unilaterally constrained structure. The structural damping matrix is approximately evaluated according to Rayleigh's method. Response spectra to a strong motion vertical acceleration earthquake record provide an initial guideline into the pipeline stability. Peak dynamic and static bending stresses are calculated for a case study involving two submarine pipeline crossings. Complete, partial and lack of pipeline gravel cover is assumed in the analysis. A seabed profile alteration, due to probable soil liquefaction, is furthermore imposed, in order to investigate the subsequent effect upon the dynamic pipeline stresses.

Recent Aeolian Origin of Surficial Gypsum Crusts in Southern Tunisia: Geomorphological, Archaeological and Remote Sensing Evidence

Recent quarring of the surficial gypsum crusts adjacent to Djebel Sidi Bou Hellas has revealed sections typically showing a discontinuous surface gravel cover underlain by more than 7 m of microcrystalline gypsum. The location, elongate shape, form in cross-section and chemistry of this deposit suggests an aeolian origin, whereby aeolian sands have been trapped against a glacis d'erosion terrace, and subsequently consolidated by meteoric waters. One gypsum quarry revealed a midden and the remains of a Roman dwelling now buried within the crust. A radiocarbon date of organic matter in the midden and a Roman coin found within it suggest an age of AD324–345 for the deposit. This is the first firm date for a surficial gypsum crust in southern Tunisia and the age is surprisingly young. Previous studies have speculated on phases of crust development between the Villefranchian and early Holocene but none since. Remote sensing and field evidence show that gypsiferous sands are currently deflated from the dry parts of the mudflats of Chott Fedjaj. They are subsequently transported in a southwesterly trajectory and trapped against glacis on the southern margins of Chott Fedjaj, forming contemporary analogues of the Roman deposit. Sands that are not trapped form dune fields and sandflats where gypsum crusts appear to be forming today. If the source area of gypsum sands has remained constant since Roman times, then the predominant wind direction has moved 45° to the southwest since then. The other possible source of aeolian gypsum for the Roman deposit, the vast mudflats of Chott Djerid, involves an even greater change in predominant wind direction. © 1997 John Wiley & Sons, Ltd.

Recent Aeolian Origin of Surficial Gypsum Crusts in Southern Tunisia: Geomorphological, Archaeological and Remote Sensing Evidence

Recent quarring of the surficial gypsum crusts adjacent to Djebel Sidi Bou Hellas has revealed sections typically showing a discontinuous surface gravel cover underlain by more than 7 m of microcrystalline gypsum. The location, elongate shape, form in cross-section and chemistry of this deposit suggests an aeolian origin, whereby aeolian sands have been trapped against a glacis d'erosion terrace, and subsequently consolidated by meteoric waters. One gypsum quarry revealed a midden and the remains of a Roman dwelling now buried within the crust. A radiocarbon date of organic matter in the midden and a Roman coin found within it suggest an age of AD324–345 for the deposit. This is the first firm date for a surficial gypsum crust in southern Tunisia and the age is surprisingly young. Previous studies have speculated on phases of crust development between the Villefranchian and early Holocene but none since. Remote sensing and field evidence show that gypsiferous sands are currently deflated from the dry parts of the mudflats of Chott Fedjaj. They are subsequently transported in a southwesterly trajectory and trapped against glacis on the southern margins of Chott Fedjaj, forming contemporary analogues of the Roman deposit. Sands that are not trapped form dune fields and sandflats where gypsum crusts appear to be forming today. If the source area of gypsum sands has remained constant since Roman times, then the predominant wind direction has moved 45° to the southwest since then. The other possible source of aeolian gypsum for the Roman deposit, the vast mudflats of Chott Djerid, involves an even greater change in predominant wind direction. © 1997 John Wiley & Sons, Ltd.

Comparative study on reduction of cooling loads by roof gravel cover

The increase in demand for power to meet the ascending energy used for air conditioning in arid areas calls for new techniques to lower the cooling loads. In this paper a simple inexpensive method is suggested, where the thermal resistance of the building roof is increased by adding a layer of loose gravel. The gravel properties as well as the intergranular trapped air reduces the heat transfer through the roof. This technique is investigated experimentally for actual outdoor weather conditions. The results show that the effect of the gravel mass intensity is more pronounced than the size of the gravel. A factor that relates the heat transfer through the gravel covered layer to that of blackened concrete roofs is suggested on the basis of the present experimental results.

97/00583 Comparative study on reduction of cooling loads by roof gravel cover

97/00583 Comparative study on reduction of cooling loads by roof gravel cover

Darcy-Weisbach Roughness Coefficients for Surfaces with Residue and Gravel Cover

Several types of hydraulic resistance factors may be present on upland agricultural areas. It is not known whether roughness contributions from individual elements are additive or if interactions between resistance factors may occur. In this study, Darcy-Weisbach roughness coefficients were measured on surfaces containing corn-soybeans, sorghum-cotton, and sunflower-wheat residue in addition to gravel cover. Varying rates of flow were introduced into a flume in which residue and gravel materials were securely attached. Roughness coefficients were calculated from measurements of discharge rate and flow velocity for Reynolds number values varying from approximately 1,200 to 13,000. The laboratory data were then used to identify the contribution to total hydraulic resistance provided by the different types of resistance elements. For most of the experimental treatments, the addition of smaller diameter residue materials (soybeans, cotton, or wheat) to surfaces containing larger resistance elements (corn, sorghum, or sunflower) did not significantly affect hydraulic resistance. However, smaller diameter residue materials did influence hydraulic resistance when they substantially increased the total volume of resistance elements. Existing roughness coefficient values were not significantly affected by the presence of gravel materials with diameters similar to the larger residue materials. The experimental results suggest that total hydraulic resistance cannot be predicted by simply adding the contributions provided by individual resistance elements. When estimating total hydraulic resistance on upland agricultural areas, the relative size, number, and volume of resistance elements must be considered.

Plant Cover and Water Balance in Gravel Admixtures at an Arid Waste‐Burial Site

AbstractIsolation of radioactive waste buried in unsaturated zones will require long‐term control of recharge and erosion. Soil covers control recharge at arid sites by storing rainwater close enough to the surface to be removed by evapotranspiration. Surface layers of rock or gravel control erosion at sites with sparse vegetation, but can also alter plant habitat and cause recharge through interred waste. As an alternative, gravel mixed into the uppermost soil layer may control erosion over the long‐term better than surface gravel layers. We postulated that gravel admixtures also would not influence plant establishment or soil water balance in waste‐site covers. We measured the interactive effects of gravel admixture concentration, vegetation, and precipitation on soil water content and plant cover at the U.S. Department of Energy's Hanford Site in Washington state. Our results support the use of a combination of vegetation and gravel admixtures for erosion control. Vegetation seasonally depleted rootzone water storage to about 6.5 volume % regardless of precipitation amount or the presence of gravel admixture amendments. In contrast, yearly increases in soil water storage as deep as 225 cm in plots without vegetation may be a leading indicator of recharge. The composition and abundance of vegetation changed over time and in response to precipitation amount, but was not influenced by gravel amendments. Seeded wheatgrasses [Agropyron sibericum Wilde and Agropyron dasystachyum (Hook.) Scribn.] established only when irrigated with twice average precipitation (32 cm/yr), but persisted after the irrigation ceased. Cheatgrass (Bromus tectorum L.) and Russian thistle (Salsola kali L.) colonized areas that received both irrigation and ambient precipitation. Stands with wheatgrasses extracted water more rapidly and depleted soil water to lower levels than cheatgrass‐dominated stands. Increases in gravel cover and near‐surface gravel concentrations after 5 yr were evidence of the formation of a protective gravel veneer.

Resistance to overland flow on semiarid grassland and shrubland hillslopes, Walnut Gulch, southern Arizona

One hundred and thirty six experiments were conducted on runoff plots on semiarid grassland and shrubland hillslopes at Walnut Gulch, Arizona. Graphs of Darcy-Weisbach friction factor f against Reynolds number Re are positively sloping or convex-upward for the grassland and predominantly negatively sloping for the shrubland. These trends are attributed to the progressive inundation of the roughness elements, with the submergence of the gravel on the shrubland being greater than the submergence of the plants on the grassland. The f-Re relations are of little value as models for predicting flow resistance at locations other than where they were developed because each location has its own unique relation which is a function of the surface properties at that location. Consequently, multivariate models that include surface properties among their predictive variables were derived for the grassland and shrubland hillslopes using multiple regression analysis. On the grassland 69.5% of the variation in f is accounted for by basal plant stem and litter cover, whereas on the shrubland 56.3% of the variation is explained by gravel cover and gravel size. The inclusion of Re improves the explained variation by 5.4% on the grassland and 7.6% on the shrubland. These results suggest that for most purposes the extra effort involved in measuring or modeling flow rate is not worth the small improvement in predictive accuracy and, therefore, that the practice of estimating resistance to overland flow solely on the basis of surface properties is entirely reasonable. A comparison of the two sets of experiments reveals that both infiltration and resistance to flow are higher on grassland than shrubland. Consequently, where shrubland has replaced grassland during the past century, in addition to the ground surface becoming more exposed to raindrop impact, overland flow has increased in volume and velocity. Together these changes have resulted in accelerated erosion in the form of rill development and stripping of the soil A horizon.

Infiltration into Sealed Soils as Influenced by Gravel Cover

AbstractThe influence of stone gravel on water infiltration is not thoroughly understood, in that previous studies led to contradictory results. This field work was conducted to determine the effect of gravel on infiltration into sealed soils and to develop a regression model for infiltration based on the areas of the exposed and covered surfaces. Data were collected on 11 soils from three great groups from the fringe of the Sahara to the wet savanna zone of West Africa. A portable rainfall simulator was used to simulate rainfall on 28 undisturbed 1 by 1 m plots. Surface slope (P), portions of surface areas covered by grass vegetation (V), coarse fragments partly embedded in a surface seal (E), free coarse fragments (F), and sealed patches (S) were assessed as well as mean diameters (MD) of coarse fragments. The surface coverage by free surface gravel alone accounted for 68% of the variance of the cumulative infiltration/rainfall ratio, denoted as the infiltration ratio (IO). A simple nonlinear model taking into account S, F, and MD resulted in a high coefficient of determination of IO (R2 = 0.95). This model tested with three other sets of data was regarded as satisfactory to predict IO (r2 = 0.87). The results suggest that infiltration rate (IR) could be better related to the effective infiltrating annulus (AN) along the perimeter of free gravel than to the whole area under the free gravel (F). Moreover, simulated results indicated that IR increased with increasing F for MD < 0.029 m. For higher values of MD, IR decreased with increasing F. Thus, in the regions where large gravel‐size coarse fragments prevail, infiltration decreases with increasing stone cover, especially if the stones are embedded in a surface seal, as in desert pavements. Conversely, infiltration is enhanced by stone cover where small free coarse fragments are dominant, like those originating from a dismantled Fe pan.

Cretaceous‐Eocene (Laramide) landscape development and Oligocene‐Pliocene drainage reorganization of transition zone and Colorado Plateau, Arizona

Landscape development of central and northern Arizona can no longer be ascribed mainly to events of Miocene and Pliocene age. New information on the age and distribution of older Cenozoic deposits has led to the recognition of a regional Cretaceous‐Paleocene(?) surface of erosion that conforms to major elements of the present topography and to the recognition that a formerly thick deposit of gravel accumulated on this regional surface of erosion. These relations cast new light on the history of evolution of the landscape and indicate a much greater age for the main landscape elements and a more complicated and prolonged history of erosion and deposition than has been previously supposed. The timing of events postulated for development of drainage on the Colorado Plateau can now be compared and partly reconciled with events recognized in the adjacent closely related Mountain Region (Transition Zone) of central Arizona. As a consequence of Late Cretaceous‐Paleocene (Laramide) compression, central and northern Arizona underwent at least 1200 m of uplift, documented by paleochannels cut into erosionally truncated Paleozoic strata on the Hualapai Plateau of the southwestern Colorado Plateau. During this time, a highly irregular erosion surface was developed on Proterozoic rocks across the Transition Zone south of the Mogollon Rim, the scarp of the Mogollon Rim was eroded to its present height (600–900 m), and an extensive stripped surface was developed on resistant upper Paleozoic strata north of the rim. Deposition of several hundred meters of Paleocene‐Eocene “Rim gravels” derived from highlands south and west of the region followed, covering much of the Cretaceous‐Paleocene erosion surface. Nearly complete burial of the rim is suggested by the distribution of remnants of the Rim gravels across the erosional scarps and on high plateau areas north of the rim. A second increment of uplift, apparently occurring in late Eocene time and apparently recorded by a series of fission track cooling ages from the Marble and Grand canyons, is inferred to have been responsible for ending deposition of the Rim gravels, for initiating differential uplift of contemporaneous deposits (Canaan Peak and Claron formations) to their positions in the high plateaus of central Utah, and for causing the drainage reorganization required to explain the extensive removal of Rim gravels from much of the region. A southerly flowing ancestral Verde River related to the drainage reorganization removed much of the older gravel cover from the Transition Zone of central Arizona, resulting in a younger regional erosion surface having 600–900 m of relief, a surface closely approximating the Cretaceous‐Paleocene erosion surface. Late Oligocene and early Miocene rocks locally rest unconformably on remnants of Rim gravels in the Transition Zone, indicating that the second episode of regional erosion had been completed by late Oligocene time. North of the Mogollon Rim, a west flowing(?) ancestral Colorado River is inferred to have become established on the Rim gravels, draining the interior parts of the Colorado Plateau and transporting detritus off the plateau. Exhumation of the Mogollon Rim and development of 600–900 m of topographic relief in the Transition Zone by an ancestral Verde River system suggests the potential for a comparable, coeval entrenchment of an ancestral Colorado River in Paleozoic strata north of the Mogollon Rim. Regional extension and volcanic activity ensued in late Oligocene to Pliocene time. The Oligocene erosion surface in the extensional basins of central Arizona became largely concealed by Miocene and Pliocene deposits as the Neogene climate became drier. In late Miocene and Pliocene time, perennial streams appear to have been lacking, transport of detritus appears to have been principally by flash flooding, little or no detritus appears to have been removed from the region, and much of the precipitation presumably moved by groundwater flow through the deposits of aggradation. A coeval episode of aggradation in the Grand Canyon is suggested by deposits that appear to have once choked much of the canyon. If this event parallels the episode of late Miocene and Pliocene aggradation recorded east, south, and west of the Grand Canyon, the Colorado River could have been incised to its present level by late Miocene time. A return to wetter conditions in late Pliocene time presumably was responsible for renewed erosion and reexcavation of older drainages and basins. An understanding of this Tertiary structural, erosional, and depositional history can be important for the geological analysis of geophysical transects across the region.

Infiltration and Sediment Production as Affected by Soil Surface Conditions in a Shrubland of Patagonia, Argentina

Infiltration and sediment production of eroded and uneroded shrub interspace soils were evaluated in December 1986 in a severely grazed, arid range site in northeastern Patagonia. A rainfall simulator and small plots were used to collect the data. A desert pavement embedded in a vesicular crust characterized the surface soil of the eroded areas that occupy the lowest position in the microtopographic pattern. A granular, fine, and weak structured A horizon characterized the soil of uneroded areas. Slopes were similar for the eroded and uneroded areas. Surface soil bulk density, electrical conductivity, clay and organic matter content were significantly greater for the eroded than for the uneroded soils. Litter cover was significantly higher for the uneroded soils. Plant cover, although higher for the uneroded areas, was low (& 5%) for both eroded and uneroded areas. Mean infiltration rate at the end of 35 min, with the soil initially dry, was 0.8 and 6.1 cm/hr for the eroded and uneroded soils. respectively. For the soil initially at field capacity, infiltration decreased to 0.6 cm/hr and 4.1 cm/hr. Soil losses were higher from the eroded areas (606 kg/ha and 687 kg/ha) than for the uneroded areas (291 kg/ha and 556 kg/ha) when the soils were initially dry and at field capacity, respectively. Regression analysis indicated infiltration rate was positively related to litter cover and negatively related to gravel cover, whereas sediment production was negatively related to bulk density, plant, and gravel cover characteristics of the site.

Late Cenozoic Pull-Apart Graben Development, Big Bend Region, Texas: ABSTRACT

The Big Bend region is a giant rhomb-shaped structure with the Presidio (west) and Black Gap (east) pull-apart grabens marking the north-northwest-trending ends and the north and south branches of the Texas lineament (TL) marking its west-northwest-trending strike-slip ends. This large rhomb is broken internally by many faults (west, west-northwest, and north-northwest trends) that have generated numerous small to large pull-apart grabens. Black Gap graben is divided into segments by west-northwest faults that drop each segment deeper (250-1,050 m, 820-3,450 ft, structural relief) and southeastward in the United States part. The continuation into Mexico has not been studied. Presidio graben also has a complex bounding fault pattern of north-northwest-, west-northwest-, and west-trending segments. Depth of the graben in unknown, although outcrop and well data give a minimum of 800 m (2,600 ft). The internal shape is poorly known because of widespread pediment gravel cover. The Presidio and Black Gap grabens are the southeastern continuation of the Rio Grande graben system that terminates southward against the north-branch of the TL (that extends from El Paso to Valentine Black Gap across Texas). The south-branch of TL extends east-southeast from near Presidio across Mexico to the Gulf of Mexico near the mouth of the Rio Grande. Right slip along the west-northwest trends is demonstrated in the Sierra del Carmen by slickensides and by a first-motion study of the Valentine earthquake. Strike-slip displacement is presumably modest across the region (under 10 km, 6 mi, ?), but actual slips are indeterminate with the present data set. The Presidio graben lies along the eastern boundary of the Laramide Chihuahua overthrust belt. The Black Gap graben lies along the eastern boundary of the Laramide Rocky Mountain front. End_of_Article - Last_Page 510------------

Multivariate Analysis of Alpine Snow-Patch Vegetation Cover near Milner Pass, Rocky Mountain National Park, Colorado, U.S.A.

This study attempts to quantify alpine snow-patch vegetation-soil communities with respect to distance from the center of the snow patch on north and south sites. Discriminant models using vegetation and environmental parameters were developed for determining differences within transects and between sites using four snow patches on northand southfacing slopes in Rocky Mountain National Park, Colorado. Data for two independently selected snow patches were used to validate the model. Collected vegetation data included cover by species while soil measurements included temperature, moisture tension, pH, percent organic matter, and texture. Slope, aspect, snow depth, and distance of the quadrat from the snow-patch basin edge were also recorded. The species composition of contiguous vegetation stands along a transect were statistically different on a multivariate basis but few univariate differences were observed. Trifolium parryi occurred more in the inner stands of the south site while T. dasyphyllum had larger cover, values in the outer stands. On the north site, however, T. parryi, Artemisia norvegica, and Geum rossii had more cover in outer stands while Deschampsia caespitosa occurred more in inner stands. Although T. parryi occurred at different distances on the two slopes, the microsites it occupied were similar in moisture and snow cover characteristics. Vegetation differed between slopes, and validation stands could be properly assigned to aspects based on a discriminant function which contained pH or gravel percentage and cover for species with small amounts of cover, such as Lewisia pygmaea, Thlaspi alpestre, or Solidago decumbens.

The Bingham copper deposits, Utah, as an exploration target; history and pre-excavation geology

The Bingham mining district was discovered in 1863, shortly after Caucasian civilization reached the Great Basin. For many decades argentiferous galena-sphalerite ores were produced from steeply dipping veins and bedded replacement deposits. Copper occurrences were known, but largely uneconomic. Recognition of the copper-rich mineralized porphyry body at the center of the district had occurred by the end of the 19th century. Breakthroughs in mining technology were required to make the deposit minable, but once begun the mine rapidly became the largest in the northern hemisphere. Large contact metasomatic copper deposits also were developed in limestone units adjacent to the Bingham stock. A number of careful workers, both famous and forgotten, contributed to the general knowledge of base metal deposits at Bingham. A major lawsuit led to careful studies of the replacement deposits by noted experts.Prior to mining, the Bingham porphyry copper deposit was characterized by a leached, iron oxide-rich capping, typically containing several tenths of one percent copper and also traces of gold. Telluride minerals were present locally. Coarse placer gold and boulders of ferruginous conglomerate occurred in adjacent drainages. The larger high-grade veins of the district radiated from or occurred near the boundaries of the mineralized portion of the stock.Deep underground workings followed lead-zinc ores to 5,000 feet vertically beneath the surface and work is now in progress to mine copper ores below the 3,300-foot level of the old underground mines. Open-pit mining has reached depths of 2,500 feet below the original outcrops.The district contains a very barren pluton (Last Chance stock) and a metal zoning pattern that extends only relatively short distances outward into country rock. A few square miles of gravel cover could have effectively concealed the highly economic copper-rich center of the district.

Gravelly flood deposits of Irvine Creek, Ontario, Canada

ABSTRACTIn May 1974 a powerful flood flushed the Grand River basin, Ontario. The effects on the bedload were drastic in a narrow (30 m) and deep (40 m) rock walled and floored gorge near Elora, Ontario. Along Irvine Creek, the tributary occupying the gorge, the gravel cover was reworked in several types of bars, predominantly transverse and point bars. The bars formed very rapidly in response to essentially steady, non‐uniform flow that developed during a brief period of high flood.Superimposed on major bars are several minor sedimentary features such as coarse transverse ribs, chute channels and bars, longitudinal ribs, imbrication clusters, backsets with well developed imbrication, that were formed under very high stream discharge. Structures like imbrication clusters, transverse ribs and small riffle bars require a ‘live bed’ situation to form, and they develop when stones come to a stop either because they cluster during transport, or because keystone effects occur along shallow channels. In Irvine Creek, very few sedimentary features were formed during waning and low flood stages: only some shadow deposits and a few Ostler lenses. The few fines that were available were lost downstream or filled in lower parts of gravel beds.This study confirms that in streams that experience strong seasonal fluctuations in discharge, bedforms that develop during high floods have a high probability of preservation. In gravelly deposits, foreset structures and plane beds are most commonly preserved, although they may be difficult to recognize in old deposits, which may appear massive, particularly if the gravel has been infilled with finer pebbles and sand. In the case of Irvine Creek, all deposits are organized, and lateral and vertical variations in textures, particularly imbrication and packing, are very useful in the recognition of sedimentary structures.

DEEP LAKE, CAPE BARNE—ANTARCTICA1

Microrelief on the ice of Deep Lake, Ross Island, Antarctica, is attributed to differential ablation, and a 3.3 m high ice cone to tilting of ice blocks beneath a gravel cover of varying thickness. The temperature of the lake water beneath the ice is thought to be a result of solar heating and the chemical stratification to be an indication that there has been an arid period in the immediate past.