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Geomorphological effects of former glacier expansion
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
The underlying topography is bound to influence the landscape of glacial deposits. When the glacier retreats across a regular plain, then one might expect subglacial and ice-marginal features to be clearly displayed. However, irregularities are introduced by hilly topography. During deglaciation an ice sheet will retreat at its margins and at the same time it will become lower and thinner. Areas of higher relief will protrude through the ice surface and isolate patches of stagnant ice in deep valleys and other depressions (Figure 19. 23). Once isolated, such stagnant ice will be charged by fluvioglacial deposits derived from both the ice surface and surrounding hills and finally melt away in situ to leave a complex topography of hummocky moraine and fluvioglacial deposits. Such a model of deglaciation seems common in the uplands of Scandinavia and Scotland.
Glacial geology
Published in Barry G. Clarke, Engineering of Glacial Deposits, 2017
As the ice moves across the basal layer (Figure 2.5), which can be bedrock, remnants of a previous glaciation or gravitationally consolidated soil, the substrate is deformed and eroded. Some of the eroded material is moved up into the glacier to be carried along by the ice (englacial debris) and some remains as a debris-rich layer continuing to be deformed. In the compression zone, the debris is deposited as till and can undergo further deformation as the ice advances. Some of the subglacial debris may be eroded by water flowing through channels within the ice, which can lead to glaciofluvial deposits in the ice if the channels are closed for some reason. As the ice melts, the glacier retreats and englacial and supraglacial debris can be deposited as a till. The melting ice carries englacial and subglacial debris beyond the ice margin to form outwash deposits. As a glacier advances and retreats, deposits are continually reworked, leading to complex deposits beneath and beyond the ice. Deglaciation at the end of an ice age led to significant changes in sea level and isostatic uplift (10–100 m), which had a significant effect on the former glaciated landscape; glaciomarine deposits become terrestrial deposits; post-glacial drainage systems lie unconformably over historic landscapes, creating a stratigraphic sequence of non-conformable deposits.
Geomorphology and Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Giovanni Barrocu, Saeid Eslamian
The following situations may occur: An upstream tectonic block of a watershed is uplifted: a knickpoint in the river profile indicates a local base level, from which erosion proceeds upstream. Consequently, The general base-level remains stable: significant erosion upstream and increased deposition downstream, with possible coastal plain formation, depending on the erosion balance between river and sea.The general base is lowered: activated erosion and downcutting of coastal plain and terraces formation, whereas headward erosion continues upstream of the knickpoint, which recedes towards the source.Subsidence of a coastal tectonic block or sea-level rise occurs due to deglaciation (changing climate). There is Erosion upstream of the knickpoint and deposition downstream: coastal plain and delta advancement, depending on the load.The danger of floods in the coastal plain with temporary or stable humid areas consisting of coastal ponds of fresh and brackish water and swamps.
Assessing the Indus Waters Treaty from a comparative perspective
Published in Water International, 2018
Global climate change will significantly impact the Indus basin’s freshwater resources, compounding the many water stresses facing the region. Global warming threatens to upset the prevailing regional precipitation patterns, shuffling the seasonal timing and geographical distribution of the rain and snow that sustain the basin’s water supplies. Fully half of the precipitation nourishing the region falls during the summer monsoon (Rajbhandari et al., 2015). Climate change will disrupt key monsoon drivers such as the moisture content of the atmosphere and temperature contrasts between the ocean and the neighbouring land surface, stirring fears that global warming could scramble the monsoon regime. Similarly, more than any other major river system, the Indus depends on the mountain glaciers surrounding its headwaters. Seasonal snow and ice meltwater contributes 35–50% of the Indus’ total flow (Savoskul & Smakhtin, 2013). As climate change lifts temperatures and skews precipitation patterns, Himalayan glaciers are receding. Recent analyses estimate that Indus Basin glaciers annually shed 7 billion metric tonnes of ice in 2003–2008 (Kääb, Treichler, Nuth, & Berthier, 2015). Initially, increased melting could boost river flows, exacerbating flood risks. As deglaciation continues, meltwater flows will wane, diminishing the downstream supplies available for drinking, sanitation, agriculture, hydropower, industry and ecosystems (National Research Council, 2012).