Home About us Contact
|
Home About us Contact | ||
|
|
||
Valley Sides (valley + side)
Selected AbstractsThe effect of terrace geology on ground-water movement and on the interaction of ground water and surface water on a mountainside near Mirror Lake, New Hampshire, USA,HYDROLOGICAL PROCESSES, Issue 1 2008Thomas C. Winter Abstract The west watershed of Mirror Lake in the White Mountains of New Hampshire contains several terraces that are at different altitudes and have different geologic compositions. The lowest terrace (FSE) has 5 m of sand overlying 9 m of till. The two next successively higher terraces (FS2 and FS1) consist entirely of sand and have maximum thicknesses of about 7 m. A fourth, and highest, terrace (FS3) lies in the north-west watershed directly adjacent to the west watershed. This highest terrace has 2 m of sand overlying 8 m of till. All terraces overlie fractured crystalline bedrock. Numerical models of hypothetical settings simulating ground-water flow in a mountainside indicated that the presence of a terrace can cause local ground-water flow cells to develop, and that the flow patterns differ based on the geologic composition of the terrace. For example, more ground water moves from the bedrock to the glacial deposits beneath terraces consisting completely of sand than beneath terraces that have sand underlain by till. Field data from Mirror Lake watersheds corroborate the numerical experiments. The geology of the terraces also affects how the stream draining the west watershed interacts with ground water. The stream turns part way down the mountainside and passes between the two sand terraces, essentially transecting the movement of ground water down the valley side. Transects of water-table wells were installed across the stream's riparian zone above, between, and below the sand terraces. Head data from these wells indicated that the stream gains ground water on both sides above and below the sand terraces. However, where it flows between the sand terraces the stream gains ground water on its uphill side and loses water on its downhill side. Biogeochemical processes in the riparian zone of the flow-through reach have resulted in anoxic ground water beneath the lower sand terrace. Results of this study indicate that it is useful to understand patterns of ground-water flow in order to fully understand the flow and chemical characteristics of both ground water and surface water in mountainous terrain. Copyright © 2007 John Wiley & Sons, Ltd. [source] Geomorphic and sedimentological signature of a two-phase outburst ,ood from moraine-dammed Queen Bess Lake, British Columbia, CanadaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2005Jane A. Kershaw Abstract On 12 August 1997, the lower part of Diadem Glacier in the southern Coast Mountains of British Columbia fell into Queen Bess Lake and produced a train of large waves. The waves overtopped the broad end moraine at the east end of the lake and ,ooded the valley of the west fork of Nostetuko River. The displacement waves also incised the out,ow channel across the moraine. Stratigraphic and sedimentologic evidence supports the conclusion that the ,ood had two phases, one related to wave overtopping and a second to breach formation. Empirical equations were used to calculate the peak discharge of the ,ood at various points along the west fork of the Nostetuko valley and to describe the attenuation of the ,ood wave. The velocity of the ,ood was also calculated to determine the time it took for the ,ood to reach the main fork of Nostetuko River. The highest peak discharges were achieved in the upper reach of the valley during the displacement phase of the ,ood. Peak discharge declined rapidly just below the moraine dam, with little change thereafter for approximately 7 km. Empirical formulae and boulder measurements indicate a rise in peak discharge in the lower part of the west fork valley. We suggest that ,ow in the upper part of the valley records the passage of two separate ,ood peaks and that the rise in discharge in the lower part of the valley is due to amalgamation of the wave and breach peaks. Hydraulic ponding in con,ned reaches of the valley extended the duration of the ,ood. In addition, erosion of vegetation and sediment in the channel and valley sides may also have exerted an in,uence on the duration and nature of ,ooding. Sediments were deposited both upstream and downstream of channel constrictions and on a large fan extending out into the trunk Nostetuko River valley. This study extends our understanding of the variety and complexity of outburst ,oods from naturally dammed lakes. It also shows that simple empirical and other models for estimating peak discharges of outburst ,oods are likely to yield erroneous results. Copyright © 2005 John Wiley & Sons, Ltd. [source] THE RESPONSE OF PARTIALLY DEBRIS-COVERED VALLEY GLACIERS TO CLIMATE CHANGE: THE EXAMPLE OF THE PASTERZE GLACIER (AUSTRIA) IN THE PERIOD 1964 TO 2006GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2008ANDREAS KELLERER-PIRKLBAUER ABSTRACT. Long-term observations of partly debris-covered glaciers have allowed us to assess the impact of supra-glacial debris on volumetric changes. In this paper, the behaviour of the partially debris-covered, 3.6 km2 tongue of Pasterze Glacier (47°05,N, 12°44,E) was studied in the context of ongoing climate changes. The right part of the glacier tongue is covered by a continuous supra-glacial debris mantle with variable thicknesses (a few centimetres to about 1 m). For the period 1964,2000 three digital elevation models (1964, 1981, 2000) and related debris-cover distributions were analysed. These datasets were compared with long-term series of glaciological field data (displacement, elevation change, glacier terminus behaviour) from the 1960s to 2006. Differences between the debriscovered and the clean ice parts were emphasised. Results show that volumetric losses increased by 2.3 times between the periods 1964,1981 and 1981,2000 with significant regional variations at the glacier tongue. Such variations are controlled by the glacier emergence velocity pattern, existence and thickness of supra-glacial debris, direct solar radiation, counter-radiation from the valley sides and their changes over time. The downward-increasing debris thickness is counteracting to a compensational stage against the common decrease of ablation with elevation. A continuous debris cover not less than 15 cm in thickness reduces ablation rates by 30,35%. No relationship exists between glacier retreat rates and summer air temperatures. Substantial and varying differences of the two different terminus parts occurred. Our findings clearly underline the importance of supra-glacial debris on mass balance and glacier tongue morphology. [source] Quaternary landscape evolution: a framework for understanding contemporary erosion, southeast SpainLAND DEGRADATION AND DEVELOPMENT, Issue 2 2002A. E. Mather Abstract Recent research into the long-term landscape development of a tectonically active terrain in arid SE Spain has revealed the significance of river capture in understanding current landscape instabilities (badlands and landslides). The river capture was initiated at c.100,ka,BP and effected a 90,m base-level change at the point of capture. This stimulated a wave of incision to propagate through the landscape to 20,km upstream of the capture site. The net effect of the associated increase in erosion has been to change valley shapes from broad and shallow to narrow and deep. The associated unloading and steepening of valley sides has led to a focus of landslide activity in lithologies with more unconfined compressive strength (limestones) and a dominance of gullying, piping and badland development in the lithologies with lower unconfined compressive strengths (marls and sands). Post-capture rapid valley widening was initially achieved through landslide development. This form of slope degradation was sustained in the more resistant, joint-controlled lithologies. In weaker lithologies it was superseded by badland development. The elevated sediment fluxes associated with the c.100,ka,BP base-level perturbation will continue into the near future, but are expected to decay, assuming that no additional environmental disturbances occur. The patterns of landscape instability witnessed today are controlled by (1) proximity to the areas affected by the base-level change and (2) the robustness of the local geology. Understanding of this long-term temporal context of the landscape provides a valuable spatial and temporal framework for land system management, facilitating the prediction of future natural trends in landscape stability. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||