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Recharge from precipitation
Published in Ian Simmers, I. Simmers, J.M.H. Hendrickx, G.P. Kruseman, K.R. Rushton, Recharge of Phreatic Aquifers in (Semi-) Arid Areas, 2017
Jan M.H. Hendrickx, Glen R. Walker
A classical example of localized recharge occurs in the numerous depressions dotting the Great Plains of North America. These features can measure tens to thousands of metres across, are often occupied by wetlands or lakes and are referred to as ‘potholes’, ‘sloughs’, or ‘playas’. Meyboom (1966) was one of the first investigators to quantify localized recharge during a one-year study of a till plain pothole with a watershed contributing area of 0.8 ha in south-central Saskatchewan (Canada). His pothole has a bottom diameter of 40 m and the height of its surrounding rim varies between 3 and 8 m. It was determined that the pothole or local depression, with 15% of the total surface area, contributed 70% of the recharge. Other investigators have also reported studies that confirm the large contribution of localized recharge described by Meyboom (1966); examples are Freeze & Banner (1970), Miller, et al. (1985), Winter (1986). Using chemical techniques, Wood & Sanford (1995) estimated that approximately half (4 to 5 mm/year) the annual recharge (9 to 10 mm/year) to the Ogallala Aquifer on the southern High Plains in the USA occurs through playa floors that cover only 6% of the area.
On the Specification of the Information Available for the Perception and Description of the Natural Terrain
Published in Peter Hancock, John Flach, Jeff Caird, Kim Vicente, Local Applications of the Ecological Approach to Human-Machine Systems, 2018
Robert R. Hoffman, Richard J. Pike
Most statements in the TAD rely on adjectival descriptors, verifying the hypothesis that generic descriptors are essential to terrain analysis. The adjective-free statements tend to be references to Relief (e.g., hills have relief less than 300 m), to Drainage (e.g., drainage patterns in a till plain are controlled by the underlying rock), and to Associated Implications that merely asserted the presence of a form or feature (e.g., ponds are present in outwash plains). Because it is unlikely, or apparently difficult, to refer to image tones without using adjectives, the number of adjective-free predications referring to Tones is very small. Conversely, it is relatively easy to refer to Formation Processes without using adjectives (see Table 10.4).
Genesis of hummocks found in tunnel valleys: an example from Hörda, southern Sweden
Published in GFF, 2018
Gustaf Peterson, Mark D. Johnson, Sandra Dahlgren, Tore Påsse, Helena Alexanderson
The Hörda valley cuts through a drumlinized till plain. The valley trends NNE to SSW, which is sub-parallel to the former ice-flow direction as shown by nearby glacial lineations (Fig. 2). The valley can be traced for at least 15 km and is about 1 km wide and approximately 10 to 20 m deep. The surficial deposits, both within and outside the Hörda valley are mapped as sandy till with pockets of surficial peat (Daniel 1986). Within the valley, there are irregular hills (hummocks), round to elongate, that are 20–150 m in diameter and with a relief of about 10 m. The hummocks at the study site are superposed by a small discontinuous esker that follows the valley floor (Fig. 2). Valley cross-profiles show that some hummock tops are concordant with the surrounding till plain (Fig. 2). Well-drilling reports just outside the rim of the valley indicate depths to bedrock from 12 to 33 m (Geological Survey of Sweden 2017). Bedrock outcrops in a few places on the valley floor which suggests that bedrock is close to the surface along the valley floor. A center line profile along the tunnel valley shows an adverse slope along its length, with the highest point half way down the valley (Fig. 2).
Drumlins in the Nordenskiöldbreen forefield, Svalbard
Published in GFF, 2018
Lis Allaart, Nina Friis, Ólafur Ingólfsson, Lena Håkansson, Riko Noormets, Wesley R. Farnsworth, Jordan Mertes, Anders Schomacker
The surface diamicton occurring at all stratigraphical sections – unit 3 at sites 1 and 2 and unit 2 at site 3 – is also interpreted to be subglacial traction till from a subsequent advance of Nordenskiöldbreen. The diamictic nature, the preferred orientation shown by the fabric analysis in unit 2 at site 3, the occurrence of striated and lodged boulders, the fluted surface and the occurrence of bullet-nosed clasts supports the interpretation of this being a subglacial traction till (Krüger & Kjær 1999; Evans et al. 2006). The unit can be traced over large parts of the forefield, and is mapped as subglacial till plain (Fig. 6). The abundant shell fragments indicate that the till is partly composed of re-worked marine sediments. It is interpreted to have been deposited during the latest advance of Nordenskiöldbreen (Slater 1925; Rachlewicz et al. 2007; Ewertowski et al. 2016).
Equifinality in glacial geomorphology: instability theory examined via ribbed moraine and drumlins in Sweden
Published in GFF, 2018
Per Möller, Thomas P. F. Dowling
Insight into the upper part of the sediment succession beneath the streamlined till plain is revealed in a small sand pit ~2 km NW of Rydaholm (white circle marked by “R” in Fig. 18), exposing 5.3 m of sorted sediment beneath a 1.7-m-thick diamict (inset log in Fig. 18). The sorted sediment succession predominantly consists of parallel-laminated medium to fine sand with floating outsized clasts (usually 3–15 cm; MPS 30 cm), interbedded with thicker units (10–40 cm) of massive gravelly sand. The beds within the sorted sediment succession plunge ~18° towards the WSW. The site-average OSL age for the sorted sediment sequence is 49 ± 3 ka, based on three OSL ages (Möller & Murray 2015), that is, within the frame of the older MIS 3 OSL age group. The sorted sedimentary succession is interpreted as a subaqueous delta-front deposit, the sedimentary structures suggesting overall deposition from turbidity currents down a delta slope. The thin planar-laminated beds suggest traction deposition after fallout from suspension, with synsedimentary deposition of avalanching coarser clasts, whereas the thicker normally graded and massive beds suggest direct suspension settling from fully turbulent flows or freezing of high-density flows where the coarser clasts were held in suspension due to dispersive pressures (e.g., Lowe 1982; Postma et al. 1988). The succession ends with a sharp boundary with a matrix-supported, massive diamict, bearing boulders of up to 80 cm, interpreted as traction till (Evans et al. 2006).