Paraglacial Landforms Research Articles

Paraglacial landform assemblages in the Hindukush and Karakoram Mountains

The paper focuses on the evolution of debris landforms in subtropical high-mountain areas. The Karakoram and Hindukush Mountains are characterized by their high volume and variety of debris accumulations. The valley flanks are coated by unconsolidated debris slopes up to 1000 m in height. The valley floors are occupied by expansive debris-flow cones and alluvial fans with escarpment heights of over 100 m. The field investigations in over twenty valleys showed that the major part of those landforms is governed by the late and post-glacial glaciation history. A key role in this glacially-controlled landscape system is played by the slope moraines, which cover the valley flanks up to several hundred meters above the valley floor. The secondary debris supply by resedimentation processes of moraine material and glacially-induced rock failures exceed by far the primary debris production due to weathering processes. Landforms which have been formerly classified as “periglacial talus cones” rather can be considered as glacial or glacially-controlled-landforms. The identified paraglacial landforms can serve as useful palaeoclimatic indicators for the ice-age reconstruction.

Landslide geomorphology of Cayton Bay, North Yorkshire, UK

SUMMARY The geomorphology of a large coastal landslide complex at Cayton Bay, North Yorkshire, is described. The area inland of the complex is occupied by a main road and a number of properties, so knowledge of current and possible future landslide behaviour is important for planning and risk assessment. Instability at the site is associated with a number of faults that bring argillaceous Upper Jurassic rocks to sea level. These soft rocks are overlain by more resistant sandstones. The sequence is capped by a thick and variable succession of glacial sediments, comprising tills with interbedded sand and gravel lenses that were deposited during the Dimlington Stadial of the Late Devensian. In connection with a study aimed at understanding cliff instability and recession, coastal erosion and the risk to people and assets at Cayton Bay, detailed geomorphological field mapping was conducted. This identified two major landslide systems, which include a periodically active mudslide complex at Cayton Cliff, recognized by shallow scarps and benches with occasional back-tilted blocks, and an area of dormant, deep-seated landslides at Tenants’ Cliffs, which includes a number of graben and horst structures. The origins of the landslides are unclear, but probably involved a variety of processes that led to a reduction in material shear strength or increases in pore water pressures. The original failure probably occurred in the middle Holocene, around 3000 years ago, when sea level reached its approximate current position. This would have initiated erosion of Jurassic argillaceous rocks (Oxford Clay) now exposed at sea level on the coast, and probable deep-seated failure of the overlying, more competent strata (Lower Calcareous Grit). Alternatively, it is possible that retreat of the Late Devensian ice sheet triggered instability, and that the landslide complex is a paraglacial landform produced during deglaciation, around 13 000 years BP. However sea levels were then lower so erosion of the Oxford Clay is unlikely to have been a factor in its development. Contemporary instability is likely to be due to the combined effects of coastal erosion and high groundwater levels, both of which are predicted to increase in the future due to the impact of climate change, implying an increased risk to coastal assets and a need to manage and mitigate such risks.

Comparing geophysical methods for talus slope investigations in the Turtmann valley (Swiss Alps)

Three geophysical methods, ground penetrating radar, 2D-resistivity and seismic refraction were applied to two landform complexes in a high-alpine valley in Switzerland to investigate their internal structure. Results of the different methods were analysed separately, before conclusions about sediment thickness and geomorphologic implications were drawn. The results from the three methods were compared to focus on the quality of the methods and their field utility, with respect to portability of equipment, required man-power and measurement time. In this study, ground penetrating radar and seismic refraction proved to be the most suitable with respect to the quality and resolution of the subsurface information and the level of field utility. Sediment thicknesses of 15 m on a rectilinear slope and more than 30 m on a talus cone have been measured; a backweathering rate of approximately 700 mm ka − 1 was established. Furthermore, the radar delivered detailed internal sediment structure as well as interfaces between talus and rock glacier. The combined geophysical investigation produced a detailed image of the subsurface composition of the two landform complexes that enhance the understanding of the paraglacial landform evolution in this hanging valley.

Paraglacial response of steep, sediment‐mantled slopes to post‐‘Little Ice Age’ glacier recession in the central Swiss Alps

AbstractThis research assesses the morphological consequences of recent (post‐‘Little Ice Age’) paraglacial reworking of valley‐side sediment mantles in the European Alps. It aims to identify the extent and conditioning factors of slope adjustment at sites in the Swiss Alps, model the temporal pattern, and assess the rates of sediment reworking involved. Gully systems have cut into steep, high‐level lateral moraines, and debris cones have accumulated downslope. Debris flow is the dominant agent of sediment transfer. Factors controlling the extent of this activity include moraine slope gradient, relief and moisture availability. Gullies appear to have reached their maximum dimensions within ca. 50 yr of deglaciation, after which gully relief is reduced by removal of inter‐gully slopes and gully infilling (within 80–140 yr). On the most recently deglaciated terrain, minimum erosion rates average ca. 95 mm yr−1 since gully initiation, greatly exceeding ‘normal’ erosion rates in other environments. Mean annual accumulation of a single debris cone since ice retreat was calculated to be ca. 30 mm yr−1. Implications of these findings are applied to patterns of paraglacial sediment‐mantled slope adjustment, conceptualising paraglacial landscape response in terms of a sediment release exhaustion model, and paraglacial landform succession. Copyright © 2005 John Wiley & Sons, Ltd.

Style and timing of glacial and paraglacial sedimentation in a monsoon-influenced high Himalayan environment, the upper Bhagirathi Valley, Garhwal Himalaya

The Gangotri Glacier, at the source of the Ganges River, has fluctuated greatly throughout the late Quaternary in response to climatic oscillations. This has resulted in impressive moraines, paraglacial debris flow fans and terraces along the upper stretches of the Bhagirathi Valley. Cosmogenic radionuclide (CRN) dating of glacial and paraglacial landforms shows that fans, terraces and associated moraines formed approximately synchronously as the landscape readjusted to changing environmental conditions. This synchronicity suggests that fan and terrace formation is intimately related to glaciation, and that fluctuations in glacial and associated environments during times of climatic instability cause rapid sediment transfer and resedimentation of glacial landforms. The CRN dates show that all existing glacial and paraglacial landforms in the upper Bhagirathi Valley formed during the late Pleistocene and Holocene. This demonstrates that, in this high mountain environment, paraglacial and glacial landforms are eroded and resedimented within about 20,000 years. Furthermore, this testifies to the dynamic nature of glacial environments in monsoon-influenced high mountain regions.

Identificación de formas glaciales mediante imagen LANDSAT-7 ETM+ - Costa de fiordos de Patagonia Central, Chile

Este trabajo presenta rasgos geomorfologicos identificados e interpretados en imagen Landsat 7 ETM+, de zonas subaéreas adyacentes a los fiordos Peel y Penguin, en la costa de fiordos de Patagonia Central, Chile. Los mapas geomorfológicos tienen el apoyo complementario de bloques diagramas 3D. El retroceso y oscilaciones de los glaciares frente a los fiordos Penguin y Peel ha producido modernos paisajes geomorfológicos que contienen formas glaciales y paraglaciales. La distribución de depósitos glacigénicos subaéreos evidencia control topográfico sobre las líneas de flujo y posibles condiciones térmicas basaleshúmedas de los glaciares, como los campos de colinas alargadas observados en el margen distal norte del fiordo Penguin. La ubicación de varios tipos de depósitos y rasgos erosionales indica que muchos de los glaciares que hoy están confinados en sus respectivos valles posiblemente se proyectaban sobre los fiordos. Asimismo, los glaciares tributarios retrocedidos en sus respectivos valles alimentan las cuencasde los fiordos mediante flujos glaciofluviales.