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Practical examples of applications and interpretations
Published in Werner Käss, Tracing Technique in Geohydrology, 2018
The general discharge conditions from of the total karst massif can be explained through the hydrogeological and karsthydrological situatuion (Fig. 187). Caused by the at first flat, then steeper dipping of the karstified Dachstein limestone plate to the north with the deeper outcrop of the karst water table at ca. 600 m as compared to 1400 m in the south, the dominant drainage is to the north. The outcropping of the main springs is bound to the superposition of the impervious rock series of the upper nappe, so that the karst water spills over. In the northwest, where these sealing layers were removed by a glacial overdeepening (Brandecker & Maurin 1982), part of the karst water crops directly out in the gravelly valley fill or crops out as a spring at the level of the receiving stream on the banks of the river Salzach.
Coastal geomorphology
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
Most near-contemporary coastal features are dominated by the Holocene sea-level rise during the past 18,000 years or so. As we have seen, it is now suggested that even features such as barrier beaches, previously considered as evidence of coastal emergence, are now viewed as having been produced by a rise in sea level. On the other hand, drowned valleys have long attracted the attention of coastal geomorphologists. Drowned valleys (rias) are widespread, for example, in Cornwall, Brittany, northwest Spain, Virginia and Maryland; those lying at right angles to the coast (e.g. in south-west Eire) contrasting with those produced by the inundation of longitudinal fold valleys parallel to the main coastal trend (e.g. Dalmatia). Drowned glacial valleys (fjords) abound in Norway (see Section 19.2.2), the South Island of New Zealand, Chile, British Columbia, Vancouver Island and elsewhere. Some of these are very deep and their form cannot be completely explained satisfactorily by a eustatic rise of sea level. The Sogne fjord of Norway is some 1300 m deep, shallowing to a characteristic seaward threshold of 150 m. It is clear that most of this overdeepening must be due to deep glacier scour produced by thick, fast-flowing ice in zones favouring glacial quarrying. Localized quarrying may well have been assisted by: (1) Pre-glacial and interglacial frost shattering.(2) Selective glacial erosion caused, for example, by topographic confinement of an ice stream along the line of a pre-existing river valley.(3) The fact that glaciers entering the sea continue to exert the same pressure on their beds as subaerial glaciers of the same thickness until the process of floatation actually begins.
Process-based approach on tidal inlet evolution – Part 1
Published in C. Marjolein Dohmen-Janssen, Suzanne J.M.H. Hulscher, River, Coastal and Estuarine Morphodynamics: RCEM 2007, 2019
D.M.P.K. Dissanayake, J.A. Roelvink
This relation is strictly valid for infinitely long bends with fully-developed flow, when the longitudinal gradients of water depth and flow velocity vanish. It leads to the description of a point bar inside channel bends in which the transverse bed slope is only a function of the local channel centreline curvature (no overdeepening effects).
Production and preservation of the smallest drumlins
Published in GFF, 2018
J. K. Hillier, Í. Ö. Benediktsson, T. P. F. Dowling, A. Schomacker
The maximum Holocene extent of Múlajökull was reached in the LIA (1717–1758), recorded by the Arnarfellsmúlar terminal moraine (Benediktsson et al. 2015). The most substantial surges since 1924 (i.e., 1954, 1971, 1986, 1992) have terminated approximately at the remaining 1992 end moraine (Björnsson et al. 2003; Johnson et al. 2010). Also, a small surge in 2008 was observed to create a significant ice-cored moraine just distal of the present ice margin (Jónsson et al. 2014; Benediktsson et al. 2016). As such, a series of moraines outside the 1992 limit, including an overridden moraine, inboard of the Arnarfellsmúlar terminal moraine suggest that this area also experienced multiple surges during the LIA both before and after the maximum extent in the early to mid-1700s (Jónsson et al. 2014; Benediktsson et al. 2015). Thus, it is convenient to divide the forefield into two zones “inside” and “outside” the 1992 moraine based on historical surge activity. The area inside is reported to contain more elongate drumlins than outside, with respective mean elongation ratios (i.e., L/W) of 3.0 and 1.9 (Benediktsson et al. 2016). It has been hypothesised (Johnson et al. 2010; Jónsson et al. 2014; Benediktsson et al. 2016) that distal drumlins have been shaped by fewer surges than those closer to the glacier. At Múlajökull surges deposit till with a sedimentology and stratigraphy that imply net aggradation (Johnson et al. 2010; McCracken et al. 2016), so inferred thicker proglacial sediment near to the current ice margin implies more geomorphically active surges there (McCracken et al. 2016). This inference is supported by a number of lines of evidence. Topography dips away from the glacier aligned with flow parallel features (e.g., flutes) and perpendicular to terminal moraines, indicating that it reflects ice flow rather than other controls. A break in slope exists at the 1992 moraine, where the four most recent large surges have stopped. There is no evidence for bedrock control of slope, and if it is postulated to be causing up-ice dips at this site its influence is demonstrated to be subservient to ice flow by the overdeepening just upstream of the current ice margin (Björnsson 1986; Lamsters et al. 2016). Thus, a powerful aspect of the Múlajökull site is that relatively strong constraints exist on the timing and duration of geomorphic work in two zones, which is rare. This constraint allows predictions by models of how subglacial bedforms (e.g., drumlins) progressively evolve with time to be considered against observations that have quite low levels of ambiguity.