Glacial geomorphology contains information about former climate which is required for modelling global climate change. Most peaks over 5500 m in the Cordillera Occidental show signs of former glaciation although few at present support perennial ice. Cirque headwalls, large sub-parallel lateral moraines, terminal moraines and minor re-advance moraines were measured at six representative study sites, as were active and inactive rock glaciers. The largest sets of lateral moraines are assumed to have formed when glaciers were in equilibrium at the peak of the last glaciation, and a succession of minor re-advance moraines was probably deposited during retreat of the ice. The radiometric age determinations corroborate existing opinion that this retreat began in the central Andes around 14 000-11 500 years BP. Reconstructed former equilibrium lines on fourteen selected palaeo-glaciers range in altitude from 4625 m at 16°S to 4775 m at 22°S. Five methods of former ELA reconstruction were tested based on geomorphological evidence collected in the field. The results imply lowering of the ELA caused by lower temperatures and increased precipitation compared to the present. The maximum extent of glaciation in the Cordillera Occidental appears to have been reached late in the last glacier cycle because of a shortage of available moisture which inhibited glacier growth when temperatures were colder. Active rock glaciers appear to respond to the thermal rather than the hydric regime and terminate close to the 0°C isotherm which was 300 m lower during deglaciation than at present.

The classical theory of channelized subglacial drainage,due orginally to Röthlisberger (1972) and Nye (1976), considers water flow in an ice channel overlying a rigid, impermeable bed. At steady flow, creep closure of the channel walls is counteracted by melt-back due to heat dissipation, and this leads to an equilibrium relation between channel water pressure and discharge. More generally, such a balance exhibits an instability that can be used to describe the mechanics of catastrophic flood events known as `jökulhlaups'. In this thesis, we substantiate these developments by exploring a detailed model where the channel is underlain by subglacial till and the flow supports a sediment load. Attention is given to the physics of bed processes and its effect on channel morphology. In particular, we propose a theory in which the channel need not be semi-circular, but has independently evolving depth and width determined by a local balance between melting and closure, and in which sediment erosion and deposition is taken into account. The corresponding equilibrium relation indicates a reverse dependence to that in the classical model, justifying the possibility of the subglacial canals envisaged by Walder and Fowler (1994). Theoretical predictions for sediment discharge are also derived. Regarding time-dependent flood drainage, we demonstrate how rapid channel widening caused by bank erosion can explain the abrupt recession observed in the flood hydrographs. This allows us to produce an improved simulation of the 1972 jökulhlaup from Grímsvötn, Iceland, and self-consistently, a plausible estimate for the total sediment yield. We also propose a mechanism for the observed flood initiation lake-level at Grímsvötn. These investigations expose the intimate interactions between drainage and sediment transport, which have profound implications on the hydrology, sedimentology and dynamics of ice masses, but which have received little attention.

No description available.

No description available.

The evolution of the landscape of Vestfirđir, made almost entirely of volcanic rocks, is traced from the lilocene, when the oldest rocks formed, through the Pliocene and Pleistocene. Volcanic activity ceased first in the north western part leaving a basalt plateau with occasional large volcanoes protruding. Fluvial erosion, guided by a westerly dip of the plateau and tectonic lineaments, left a well developed drainage pattern there by the rime volcanic activity ceased in the southeast. The snowline fluctuated widely during the Plio-Pleistocene. Cirque and valley glaciations were very effective in sculpturing the landscape where the preglacial relief was greatest, in the northwest. Ice sheet glaciations affected the whole peninsula and offshore areas with linear erosion dominant in the northwest and areal scouring elsewhere. The glacial geomorphology of Dyrafjorour and northern Arnarfjorour is mapped. The highest marine limit is in the Nupur area, about 110 m, and shorelines and marine limits higher than 70 m are at 7 other localities at least. At least' two stages of glacial readvances are recognized: The Tjaldanes stage occurred when sea level was between 11 and 22 m and is probably of "Younger Dryas" age; later a readvance occurred in the cirques in the area. On the basis of evidence on cirque distribution, cirque elevation, zeolite zonation, distribution of glacial erosional landscapes, glacial history, marine limits, ice cap profiles and shelf moraine a model of maximum glaciations of Vestfir6ir is proposed: The whole of Vestfir6ir and the surrounding shelf areas was completely ice covered with no ice free areas. Such a stage of glaciation, the Latragrunn stage, probably prevailed in the Vestfiroir area during the last glaciation.

Patagonia has one of the most extensive and well preserved glacial geomorphic records of anywhere else in the world. This study provides empirical constraints of Patagonian Ice Sheet (PIS) configuration and dynamics during the last two glacial cycles and the Holocene at 49°S. In particular a chronology of palaeo-ice surface elevations, thickness changes and ice-thinning rates is developed. Cosmogenic surface exposure dating across eight mountain transects at Hielo Patagonico Sur (HPS) outlet glaciers' Viedma and Chico, and from eastern facing mountain valley glaciers, is utilised to reconstruct PIS ice-surface elevation changes through time. The earliest dated glacier ice thickness marker falls into MIS6 (Marine Isotope Stage). The last glacial cycle is characterised by continuous ice-surface elevation lowering from a maximum at MIS5a to the Antarctic Cold Reversal (ACR). Large scale PIS cover occurred between ca. 40-47 kyrs, in both the HPS outlet glaciers and the eastern mountain valleys. This regional ice-cover considerably pre-dates the global Last Glacial Maximum (gLGM). A gLGM vertical ice surface expression is absent from the study area. A minor re-advance and/or stillstand at ca. 18 kyrs is recorded by the valley glaciers, but is not evident at the HPS outlet glaciers. Glacier Viedma records a prominent ice elevation during the ACR with rapid thinning at the end of the climate perturbation. Ice-surface lowering from the ACR limit continues with acceleration toward the late-Holocene. The PIS palaeo-ice elevation and thinning record presented here is sensitive to internal PIS dynamics, local and global climate forcing acting on different timescales, with glacier response to climate perturbation strongly linked to glacier catchment size and distance from the main source of precipitation at 49°S.

No description available.

The factors affecting the distribution of surge-type glaciers and the causes of the surge mechanism are not fully understood. Statistical analyses of glaciers in Svalbard have been used to identify characteristics which are related to surging. Field experiments were undertaken on Bjuvbreen, a small surge-type glacier in central Spitsbergen, to determine the dynamics and hydrology of the glacier during its quiescent phase. The probability that a glacier in the Svalbard sample population was surge-type was 36·4%. The probability varied spatially within the sample area. Glaciers resting on sedimentary tocks had a greater probability of being surge-type compared to those overlying igneous or metamorphic rocks. The probability of surging was also increased in glaciers with a two-layered thermal structure as indicated by radio echo sounding. Geometrical characteristics such as slope, orientation, curvature and the presence of tributaries were not related to surge-type behaviour, although long glaciers had a greater chance of being surge-type. Certain aspects of Kamb's and Fowler's theories of surging were not supported by the statistical analysis. Despite the associations between surging and certain characteristics, no single factor fully explained the observed geographical distribution of surge-type glaciers in Svalbard. Bjuvbreen is a small surge-type in its quiescent phase. Changes in the geometry of the glacier are occurring relatively slowly. This slow rate of change is a function the low accumulation rates on Svalbard glaciers. On the basis of a simple model, the next surge of Bjuvbreen is predicted to occur between .2022- 2055, indicating a comparatively long quiescent period of -90-130 years. Bjuvbreen is comprised of two dynamically distinct zones which are separated by a large bulge. The lower portion of the glacier is inactive and stagnating, in contrast to the active ice up.:.glacier from the bulge. The observed velocity of the active region was compared with various hydrological characteristics of the glacier. The inferred behaviour of water within the glacier seems to have some, although limited, influence on the ice motion. A spatially restricted drainage system is the probable reason for this limited influence of hydrology on glacier velocity.

No description available.

No description available.