Quantification of post-glacier erosion in the European Alps using 10Be and OSL exposure dating
Joanne ElkadiBenjamin LehmannGeorgina E. KingOlivia SteinemannSusan Ivy‐OchsMarcus ChristlFrédéric Herman
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Abstract. The retreat of glaciers since the Last Glacial Maximum (LGM) in the European Alps has left an imprint on topography through glacial and non-glacial erosional processes. However, few methods are currently capable of resolving these mechanisms on Lateglacial to Holocene timescales. Quantifying the relative contributions of mountain erosion, during these different climate cycles, is useful for understanding long-term landscape evolution and the links between global climate and erosion. Here, we combine three Optically Stimulated Luminescence (OSL) exposure dating signals with 10Be surface exposure dating to constrain the post-glacier erosion rates of bedrock samples down a vertical transect adjacent to the Gorner glacier in Zermatt, Switzerland. The results reveal erosion rates on the order of 10-2 to 10-1 mm a-1, in general agreement with other studies in the region, as well as a strong negative correlation between erosion rates and elevation. Finally, at present glacial erosion is assumed to have a greater influence on landscapes, yet a global compilation of both glacial and non-glacial erosion rates in deglaciated environments shows that erosion rates during interglacial times could be equally important.Keywords:
Bedrock
Last Glacial Maximum
Elevation (ballistics)
To document and compare vascular plant species and soils present in each of two sand dune areas in Harding and Perkins Counties of northwestern South Dakota, six transects were established. Two transects ran across dune tops, two in parallel swales and two in blowout areas. In transects monitored four times per year vascular plant species were determined for five years in Harding County and for four years in Perkins County. Eighty-three species were found in transects in Harding County, and 75 species were found in the Perkins County transects for a total of 98 species observed in the study. Relatively high numbers of native species (86-100%) were present in all transects. The mean coefficient of conser vatism of the Harding County transects was 4.5 and that of the Perkins County transects was 4.7. Floristic Quality Indices were 38.7 and 39.0 for Harding and Perkins County sites, respectively. Analyses of soil and vegetation characteristics showed that blowout transects of the two areas were most similar, and swale transects were least similar.
Swale
Belt transect
Vascular plant
Limiting
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the bedrock geologic map portrays the current interpretation of the distribution of various bedrock stratigraphic units present at the bedrock surface the bedrock surface is buried by unconsolidated surficial sediments mostly quaternary over most of its extent but this surface coincides with the modern land surface in areas of bedrock exposure the map is consistent with all available data including drill records and well samples as well as surface bedrock exposures both natural and man made and shallow to bedrock soils units nrcs county soils maps mapped stratigraphic intervals are portrayed primarily at the group level i e a grouping of bedrock formations each characterized by distinctive lithologies rock types summarized in the map key and associated metadata the distribution of bedrock units was mapped to conform to the current map of bedrock topography elevation of the bedrock surface the structural configurations of relevant stratigraphic datums were intercepted with the bedrock topographic surface to produce the map contacts the line style shown on the bedrock geologic map qualitatively reflects both data density and degree of certainty of individual stratigraphic contacts downloadable
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Lithology
Geologic map
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Analysis of topographic and bedrock surface data from 41 sites 23.3 km2 (9 m2) within Midwestern areas glaciated during the Late Wisconsinan identifies an average drift thickness-maximum bedrock relief transition equation for the presence or absence of bedrock surface influences on topographic detail. For sites with average drift thicknesses between 15 and 35 m, the transition occurs when average drift thicknesses exceed 0.5 maximum bedrock relief + 10 m. This equation may provide a practical tool in searching for buried bedrock valleys.
Bedrock
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With the combination of gradient analysis and quantitative analysis of landscape pattern,and by changing the transect width and research step,the extent effect of landscape gradient analysis of an urban-rural transect were studied.The results showed that the landscape gradient analysis of the urban-rural transect was scale-dependent,and the effect of transect width was greater than that of research step.Research step mainly affected the fluctuation degree of each landscape index along transect,and it was appropriate for the transect to be divided equally into 20 samples.There existed critical values for transect width.When the transect width was beyond the values,the fluctuation trend of each index along transect would be varied.Furthermore,different landscape metrics responded differently to the same transect.The percent coverage and edge density of each class,as well as the Shannon's diversity index of landscape,showed significant gradient characteristics,while patch density and mean patch fractal dimension were in adverse.
Belt transect
Diversity index
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Skyscrapers in Manhattan need to be anchored to bedrock to prevent (possibly uneven) settling. This can potentially increase construction costs if the bedrock lies deep below the surface. The conventional wisdom holds that Manhattan developed two business centers--downtown and midtown--because the depth to the bedrock is close to the surface in these locations, with a bedrock valley in between. We measure the effects of building costs associated with bedrock depths, relative to other important economic variables in the location of early Manhattan skyscrapers (1890-1915). We find that bedrock depths had very little influence on the skyline; rather its polycentric development was due to residential and manufacturing patterns, and public transportation hubs.
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Downtown
Skyline
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Details of ground flora in 8 transects situated in burnt and unburnt Pinus longifolia sample plots are recorded both for June and September. Species peculiar to the burnt and unburnt transects are listed. Area under blanks is greater in the burnt transects which have comparatively less vegetation. Premma hevrbacea , amongst others, is peculiar to the burnt transects. It is the first attempt of work of this kind.
Flora
Belt transect
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Significance Hilly landscapes are typically mantled with soil and underlain by a weathered bedrock zone that may extend tens of meters beneath the surface before reaching fresh bedrock. The weathered bedrock zone influences water runoff to channels, the chemistry of that water, the rates and processes of erosion, and atmospheric processes due to plant uptake of moisture and return to the atmosphere. However, the spatial pattern of the underlying fresh-bedrock surface is essentially unknown. We present a testable model that predicts hillslope form and the depth to fresh bedrock. The depth increases upslope and depends strongly on the porosity and permeability of the bedrock and the rate of channel incision at the base of the hillslope.
Bedrock
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We used data from 87 km of line transects in northern Michigan and northern Wisconsin in June 1985 to determine the optimum length of replicate transects required to assess bird populations. Data are from a study comparing bird populations in areas affected by electromagnetic fields (treatments) to those in areas unaffected (controls). Transects were subdivided into six different lengths varying from 100 m to 1,000 m. With equal effort, we were able to detect smaller differences in bird counts between control and treatment areas with short transects and large sample sizes than with long transects and small sample sizes. Transects shorter that 350 m required the smallest amount of effort to detect a 15% difference between means for number of individuals and species. The most efficient transect length for detecting a 25% difference between means was not consistent for individual species but was positively correlated with relative density. The shortest transect (100 m) was best for detecting differences for the Ovenbird (Seiurus aurocapillus), Red-eyed Vireo (Vireo olivaceus), and Nashville Warbler (Vermivora ruficapilla) the most abundant species; a 250-m transect was best for the Black-throated Green Warbler (Dendroica virens); and a 500-m transect for the least abundant species, the White-throated Sparrow (Zonotrichia albicollis).
Warbler
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The value of the number of transects within a segment of an instream flow study that will generate a stable relationship between the PHABSIM habitat index and discharge is examined. Over 600 instream flow studies were reviewed to determine the common practice standard, showing a median number of eight transects per four mile reach. Since the number of study transects varies by length of reach and purpose of study, transects per mile were computed as a more standardized value, with a median result of 2.32 transects per mile for 552 reaches. Studies conducted for water rights claims (255) had a median of 1.30 transects per mile and those conducted for project evaluations (259) had a median of 4.17 transects per mile. Several high transect number data sets were also systematically subsampled to determine how many transects are required to produce a robust habitat index function. This analysis showed that approximately 18-20 transects will in most cases yield a result nearly identical to one obtained using 40-70 transects per segment. When used for time series analysis and comparison of flow alternatives, remaining small differences in the functions would be inconsequential.If used for standard setting purposes, however, the differences could affect flow recommendations and more transects are likely to be necessary.
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