Glacio-limnological interactions at lake-calving glaciers

Iceberg calving is an efficient ablation process which introduces mechanical instability to glacier systems and can cause non-linear climatic response. This thesis uses glaciological and limnological data to examine the relative contributions of calving and melting to mass loss at glacier termini, and the interplay between glaciological and limnological processes. Calving dynamics are investigated at two lake-terminating glaciers; Glaciar Leon in Chile and Fjallsjokull in Iceland. Glaciar Leon, a temperate, grounded outlet of the North Patagonian Icefield, terminates at an active but stable calving margin in Lago Leones. The calving rate of 880 m a-1 in a mean water depth of 65 m is high for lake-calving glaciers. Detailed survey of the physical limnology of Lago Leones, important for considering heat transfer to the subaqueous ice face, revealed thermocline development towards the terminus between spring and summer. Melting at the waterline along the glacier terminus facilitates calving by undercutting the subaerial calving cliff, and accounts for around a quarter of mass loss at the terminus. Waterline melting is also an important rate-controlling process for calving at Fjallsjokull. Precise quantification of melt rates (subaerial, waterline and subaqueous) at the termini of calving glaciers is difficult and hazardous, but this study has demonstrated the value of two techniques: (1) detailed survey of melt notch growth, and (2) use of a radiocontrolled boat to record water temperatures at the ice-water interface. Continuous automated monitoring showed that lake-level fluctuations are integral to calving behaviour, influencing calving event timing and size over diurnal and hourly timescales. Fjallsjokull is sensitive to climatic forcing whereas Glaciar Leon, which exhibits larger seasonal than annual fluctuations, is less sensitive. Additional controls on calving at both sites are (1) buoyancy, (2) longitudinal stretching, and (3) the force balance at the ice-water interface. Calving operates along a continuum defined by the relative importance of interacting calving mechanisms, to which the climatic response of calving glaciers is sensitive

Glacio-limnological interactions at lake-calving glaciers

Iceberg calving is an efficient ablation process which introduces mechanical instability to glacier systems and can cause non-linear climatic response. This thesis uses glaciological and limnological data to examine the relative contributions of calving and melting to mass loss at glacier termini, and the interplay between glaciological and limnological processes. Calving dynamics are investigated at two lake-terminating glaciers; Glaciar Leon in Chile and Fjallsjokull in Iceland. Glaciar Leon, a temperate, grounded outlet of the North Patagonian Icefield, terminates at an active but stable calving margin in Lago Leones. The calving rate of 880 m a-1 in a mean water depth of 65 m is high for lake-calving glaciers. Detailed survey of the physical limnology of Lago Leones, important for considering heat transfer to the subaqueous ice face, revealed thermocline development towards the terminus between spring and summer. Melting at the waterline along the glacier terminus facilitates calving by undercutting the subaerial calving cliff, and accounts for around a quarter of mass loss at the terminus. Waterline melting is also an important rate-controlling process for calving at Fjallsjokull. Precise quantification of melt rates (subaerial, waterline and subaqueous) at the termini of calving glaciers is difficult and hazardous, but this study has demonstrated the value of two techniques: (1) detailed survey of melt notch growth, and (2) use of a radiocontrolled boat to record water temperatures at the ice-water interface. Continuous automated monitoring showed that lake-level fluctuations are integral to calving behaviour, influencing calving event timing and size over diurnal and hourly timescales. Fjallsjokull is sensitive to climatic forcing whereas Glaciar Leon, which exhibits larger seasonal than annual fluctuations, is less sensitive. Additional controls on calving at both sites are (1) buoyancy, (2) longitudinal stretching, and (3) the force balance at the ice-water interface. Calving operates along a continuum defined by the relative importance of interacting calving mechanisms, to which the climatic response of calving glaciers is sensitive.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A glacial lake outburst flood associated with recent mountain glacier retreat, Patagonian Andes

Geomorphological mapping, sedimentology, lichenometry and dendrochronology were used to assess the nature and timing of glacier recession, moraine development and catastrophic mass movements in a tributary of the Leones valley, east of the Hielo Patagonico Norte, Chile. We show that during the 'Little Ice Age' Glaciar Calafate advanced downvalley to produce a terminal moraine. Recession of the glacier from this position occurred in the 1870s and produced a moraine dammed lake. In late 2000 a large rockfall into the lake breached the moraine and triggered a glacial lake outburst flood ( GLOF) that entrained and subsequently deposited some 2 x 10(6) m(3) of material. We interpret this event as a delayed paraglacial response to the retreat of Glaciar Calafate during the twentieth century.</p

Glaciar León, Chilean Patagonia: late-Holocene chronology and geomorphology

Glaciar León is a temperate, grounded outlet of the eastern North Patagonian Icefield (NPI). It terminates at an active calving margin in Lago Leones, a 10 km long proglacial lake. We take a multidisciplinary approach to its description and use ASTER imagery and clast sedimentology to describe the geomorphology of the glacier and its associated moraines. We date periods of glacier retreat over the last 2500 years using a combination of lichenometric, dendrochronological, cosmogenic and optically stimulated luminescence techniques and show that the glacier receded from a large terminal moraine complex some 2500 years ago and underwent further significant recession from nineteenth-century moraine limits. The moraine dates indicate varying retreat rates, in conjunction with significant downwasting. The bathymetry of Lago Leones is characterized by distinct ridges interpreted as moraine ridges that dissect the lake into several basins, with water depths reaching 360 m. The fluctuations of Glaciar León appear to have been controlled by the interplay between climatic forcing and calving dynamics.</p