The influence of bedrock orientation on the landscape evolution,surface morphology and denudation (10Be) at the Niesen,Switzerland

Landscape evolution and surface morphology in mountainous settings are a function of the relative importance between sediment transport processes acting on hillslopes and in channels, modulated by climate variables. The Niesen nappe in the Swiss Penninic Prealps presents a unique setting in which opposite facing flanks host basins underlain by identical lithologies, but contrasting litho‐tectonic architectures where lithologies either dip parallel to the topographic slope or in the opposite direction (i.e. dip slope and non‐dip slope). The north‐western facing Diemtigen flank represents such a dip slope situation and is characterized by a gentle topography, low hillslope gradients, poorly dissected channels, and it hosts large landslides. In contrast, the south‐eastern facing Frutigen side can be described as non‐dip slope flank with deeply incised bedrock channels, high mean hillslope gradients and high relief topography. Results from morphometric analysis reveal that noticeable differences in morphometric parameters can be related to the contrasts in the relative importance of the internal hillslope‐channel system between both valley flanks. While the contrasting dip‐orientations of the underlying flysch bedrock has promoted hillslope and channelized processes to contrasting extents and particularly the occurrence of large landslides on the dip slope flank, the flank averaged beryllium‐10 (¹⁰Be)‐derived denudation rates are very similar and range between 0.20 and 0.26 mm yr^?1. In addition, our denudation rates offer no direct relationship to basin's slope, area, steepness or concavity index, but reveal a positive correlation to mean basin elevation that we interpret as having been controlled by climatically driven factors such as frost‐induced processes and orographic precipitation. Our findings illustrate that while the landscape properties in this part of the northern Alpine border can mainly be related to the tectonic architecture of the underlying bedrock, the denudation rates have a strong orographic control through elevation dependent mean annual temperature and precipitation. Copyright © 2013 John Wiley & Sons, Ltd.     

Erosion-driven uplift of the modern Central Alps

We present a compilation of data of modern tectono-geomorphic processes in the Central European Alps which suggest that observed rock uplift is a response to climate-driven denudation. This interpretation is predominantly based on the recent quantification of basin-averaged Late Holocene denudation rates that are so similar to the pattern and rates of rock uplift rates as determined by geodetic leveling. Furthermore, a GPS data-based synthesis of Adriatic microplate kinematics suggests that the Central Alps are currently not in a state of active convergence. Finally, we illustrate that the Central Alps have acted as a closed system for Holocene redistribution of sediment in which the peri-Alpine lakes have operated as a sink for the erosional products of the inner Central Alps.While various hypotheses have been put forward to explain Central Alpine rock uplift (e.g. lithospheric forcing by convergence, mantle processes, or ice melting) we show with an elastic model of lithospheric deformation, that the correlation between erosion and rock uplift rates reflects a positive feedback between denudation and the associated isostatic response to unloading. Thus, erosion does not passively respond to advection of crustal material as might be the case in actively converging orogens. Rather, we suggest that the geomorphic response of the Alpine topography to glacial and fluvial erosion and the resulting disequilibrium for modern channelized and associated hillslope processes explains much of the pattern of modern denudation and hence rock uplift. Therefore, in a non-convergent orogen such as the Central European Alps, the observed vertical rock uplift is primarily a consequence of passive unloading due to erosion.     

The relative influences of climate and catchment processes on Holocene lake development in glaciated regions

Following deglaciation, the long-term pattern of change in diatom communities and the inferred history of the aquatic environment are affected by a hierarchy of environmental controls. These include direct climate impacts on a lake’s thermal and hydrologic budgets, as well as the indirect affects of climate on catchment processes, such as weathering, soil development, microbial activity, fire, and vegetation composition and productivity, which affect the transfer of solutes and particulates from the terrestrial ecosystem into the lake. Some of these catchment influences on lacustrine systems operate as time-dependent patterns of primary succession that are set in motion by glacier retreat. This paper provides a conceptual model of some dominant pathways of catchment influence on long-term lake development in glaciated regions and uses a series of paleolimnological examples from arctic, boreal, and temperate regions to evaluate the relative role of direct climate influences and of catchment processes in affecting the trajectory of aquatic ecosystems during the Holocene in different environmental contexts.     

Assessing quality of volunteer crowdsourcing contributions: lessons from the Cropland Capture game

Volunteered geographic information (VGI) is the assembly of spatial information based on public input. While VGI has proliferated in recent years, assessing the quality of volunteer-contributed data has proven challenging, leading some to question the efficiency of such programs. In this paper, we compare several quality metrics for individual volunteers’ contributions. The data were the product of the ‘Cropland Capture’ game, in which several thousand volunteers assessed 165,000 images for the presence of cropland over the course of 6 months. We compared agreement between volunteer ratings and an image's majority classification with volunteer self-agreement on repeated images and expert evaluations. We also examined the impact of experience and learning on performance. Volunteer self-agreement was nearly always higher than agreement with majority classifications, and much greater than agreement with expert validations although these metrics were all positively correlated. Volunteer quality showed a broad trend toward improvement with experience, but the highest accuracies were achieved by a handful of moderately active contributors, not the most active volunteers. Our results emphasize the importance of a universal set of expert-validated tasks as a gold standard for evaluating VGI quality.     

Stormwater harvesting in ephemeral streams: how to bypass clogging and unsaturated layers

To cope with water scarcity in drylands, stormwater is often collected in surface basins and subsequently stored in shallow aquifers via infiltration. These stormwater harvesting systems are often accompanied by high evaporation rates and hygiene problems. This is commonly a consequence of low infiltration rates, which are caused by clogging layers that form on top of the soil profile and the presence of a thick vadose zone. The present study aims to develop a conceptual solution to increase groundwater recharge rates in stormwater harvesting systems. The efficiency of vadose-zone wells and infiltration trenches is tested using analytical equations, numerical models, and sensitivity analyses. Dams built in the channel of ephemeral streams (wadis) are selected as a study case to construct the numerical simulations. The modelling demonstrated that vadose-zone wells and infiltration trenches contribute to effective bypassing of the clogging layer. By implementing these solutions, recharge begins 2250–8100% faster than via infiltration from the bed surface of the wadi reservoir. The sensitivity analysis showed that the recharge rates are especially responsive to well length and trench depth. In terms of recharge quantity, the well had the best performance; it can infiltrate up to 1642% more water than the reservoir, and between 336 and 825% more than the trench. Moreover, the well can yield the highest cumulative recharge per dollar and high recharge rates when there are limitations to the available area. The methods investigated here significantly increased recharge rates, providing practical solutions to enhance aquifer water storage in drylands.

     

Discovery of ions with nuclear charge Z ≧ 9 stably trapped in the earth's radiation belts

We report observations of MeV heavy ions made with Explorer 45 in the earth's radiation belts during the 7-month period June–December 1972 when four major magnetic storms occurred. Significant fluxes of ions heavier than fluorine (i.e. with nuclear charge Z ? 9) were observed stably trapped in the interior of the radiation belts at L ～ 2–4. These energetic very heavy ions, were found to appear suddenly during the August 1972 magnetic storm period and their fluxes decayed during the following months on time scales typically several tens of days. Simultaneously, strong increases in the geomagnetically trapped MeV helium and CNO ion fluxes were observed, and the post-injection flux decay of these ions was found to be slower than that of the Z ? 9 ions. The relative enhancements in trapped fluxes during the storm increased with increasing ion mass and/or increasing ion energy.     

Erosion rates and mechanisms of knickzone retreat inferred from 10Be measured across strong climate gradients on the northern and central Andes Western Escarpment

A steep escarpment edge, deep gorges and distinct knickzones in river profiles characterize the landscape on the Western Escarpment of the Andes between ~5°S and ~18°S (northern Peru to northern Chile). Strong north–south and east–west precipitation gradients are exploited in order to determine how climate affects denudation rates in three river basins spanning an otherwise relatively uniform geologic and geomorphologic setting. Late Miocene tectonics uplifted the Meseta/Altiplano plateau (~3000 m a.s.l.), which is underlain by a series of Tertiary volcanic‐volcanoclastic rocks. Streams on this plateau remain graded to the Late Miocene base level. Below the rim of the Meseta, streams have responded to this ramp uplift by incising deeply into fractured Mesozoic rocks via a series of steep, headward retreating knickzones that grade to the present‐day base level defined by the Pacific Ocean. It is found that the Tertiary units on the plateau function as cap‐rocks, which aid in the parallel retreat of the sharp escarpment edge and upper knickzone tips. ¹⁰Be‐derived catchment denudation rates of the Rio Piura (5°S), Rio Pisco (13°S) and Rio Lluta (18°S) average ~10 mm ky^?1 on the Meseta/Altiplano, irrespective of precipitation rates; whereas, downstream of the escarpment edge, denudation rates range from 10 mm ky^?1 to 250 mm ky^?1 and correlate positively with precipitation rates, but show no strong correlation with hillslope angles or channel steepness. These relationships are explained by the presence of a cap‐rock and climate‐driven fluvial incision that steepens hillslopes to near‐threshold conditions. Since escarpment retreat and the precipitation pattern were established at least in the Miocene, it is speculated that the present‐day distribution of morphology and denudation rates has probably remained largely unchanged during the past several millions of years as the knickzones have propagated headward into the plateau. Copyright © 2011 John Wiley & Sons, Ltd.