Noralf Rye

Holocene glacial and climate history of the Jostedalsbreen region, Western Norway; evidence from lake sediments and terrestrial deposits

The valleys surrounding the Jostedalsbreen ice cap were deglaciated during the latter half of the Preboreal Chronozone. At the end of the Preboreal Chronozone, however, a glacier readvance occurred. Terminal moraines were deposited by outlet valley glaciers from the Jostedalsbreen Plateau up to 1 km beyond Little Ice Age moraines. Inferred from the altitude of lateral moraines formed during this readvance and calculations of the equilibrium-line altitude (ELA) depression based on an accumulation area ratio (AAR) of 0.6, the average depression of the ELA was 325 + 75−115 m below the present. By assuming a similar precipitation pattern as at present, this suggests a mean temperature decline of about 2°C. Palynological investigations from Sygneskardet, Sunndalen, indicate that climate like the present was achieved just after 9000 BP. The Holocene climatic optimum occurred during the Atlantic Chronozone, with elm (Ulmus) stands growing at the present birch (Betula) forest limit in Sunndalen and pine (Pinus) growing at Styggevatnet to an altitude of at least 1160 m. During this period the mean summer temperature is estimated to have been at least 2.7 and 1.8°C warmer than at present, with and without the local climatic effect of Jostedalsbreen, respectively. An inferred rise of the ELA of about 400 m from the present altitude suggests that possibly no glaciers existed on the Jostedalsbreen Plateau during the Holocene climatic optimum. Vegetational changes as deduced from palynological studies, lowered tree limits and increased resedimentation in peat bogs indicate general climatic deterioration since the Late Atlantic Chronozone. A significant Alnus decline 6300 BP and a Betula expansion 5300 BP, as recorded from palynological studies of peat bogs in Sprongdalen, is interpreted to represent the initial Neoglaciation on the Jostedalsbreen Plateau. Lithostratigraphic evidence at a section in the upper part of Glomsdalen may indicate a minor Neoglacial phase close to 6000 BP. The first pronounced Neoglacial event in the Jostedalsbreen region, however, was bracketed between 3700 and 3100 BP. Sporteggbreen, the upper part lying ca. 30 m above the present regional glaciation threshold, was formed around 500 BP at the initiation of the Little Ice Age. Gelifluction at 1000 m altitude began after 3200-2800 BP. During the Medieval Period, glaciers were smaller than now. At the northwestern part of Jostedalsbreen an initial Little Ice Age glacier expansion is dated to have occurred after 890 ± 60 BP (A.D. 1030–1220). From the early 14th century, and especially from the mid-17th century, a severe climatic deterioration during the Little Ice Age is historically documented. Around Jostedalsbreen this advance culminated during the mid-18th century. Documents suggest that the western outlet glaciers from Jostedalsbreen reached their maximum Little Ice Age position some years before the longer eastern outlet valley glaciers. A typical depression of the ELA during the Little Ice Age of 100–150 m indicates a mean temperature decline from the present of ca. 0.5–1°C.

Modern and Little Ice Age Equilibrium-Line Altitudes on Outlet Valley Glaciers from Jostedalsbreen, Western Norway: An Evaluation of Different Approaches to Their Calculation

The modern and Little Ice Age (LIA) equilibrium-line altitude (ELA) of 20 outlet valley glacier from Jostedalsbreen, western Norway, has been calculated using different approaches. Using an accumulation area ratio (AAR) of 0.6 [+-] 0.05 gave a mean little Ice Age ELA depression of 70 m. A method developed by M. Kuhle, taking the influence by topography into account gave a mean ELA depression of 35-255 m, the median elevation of glaciers 115 m, and the toe-to-headwall altitude ration 140 m. Differences in the ELA estimates can be attributed to the differences in topography and morphology of the glaciers. The AAR method appears to provide the most reliable results. This will aid in determining mean global temperatures during the LIA. 34 refs., 9 figs., 5 tabs.

The Late Weichselian ice sheet in the Nordfjord – Sunnmøre area and deglaciation chronology for Nordfjord, western Norway

Rye, N., Nesje, A., Lien, R. & Anda, E. 1987. The Late Weichselian ice sheet in the Nordfjord – Sunnmore area and deglaciation chronology for Nordfjord, western Norway. Norsk geogr. Tidsskr. Vol. 41, 23–43. Oslo. ISSN 0029-1951. Block fields, alpine morphology and glacially sculptured landforms in the Nordfjord – Sunnmore area suggest that the highest mountains in this region were never completely covered by the inland ice during the Late Weichselian maximum glaciation. A mainly NW ice drainage from the accumulation zones of the inland ice sheet in the east and a culmination area at the Jostedal Plateau were strongly influenced by effective drainage routes through the fjords and valleys. On the basis of the sequence of deglaciation and associated marine levels and radiocarbon dates, a chronology and a time-distance diagram for the deglaciation of Nordfjord are presented.

Late Holocene glacier activity at Sandskardfonna, Jostedalsbreen area, western Norway

Radiocarbon dates of tree logs from five palaeosols interlayered with distal glaciofluvial minerogenic deposits at Sandsvora, Sunndalen, a south-east tributary at Hjelledalen, Stryn, suggest that the Sandskardfonna cirque glacier upvalley from the site was in a contracted state, or had disappeared entirely, close to 620±70 yr BP (AD 1280–1405), 890 ±60 yr BP (AD 1140–1210), 1110 ±60yr BP (AD 880–990), 1180 ±70 yr BP (AD 770–900), and 1270 ±60 yr BP (AD 670–790). The radiocarbon date from the upper palaeosol in the section of 620±70 yr BP (AD 1280–1405) represents a maximum date for initiation of the Little Ice Age glacier advance of Sandskardfonna that culminated in the 18th century.

Seawater intrusion and fresh groundwater hydraulics in fjord delta aquifers inferred from ground penetrating radar and resistivity profiles. Sunndalsøra and Esebotn, western Norway

Abstract Geophysical surveys have been carried out in two fjord delta aquifers in western Norway. Geophysical methods comprised ground penetrating radar (GPR), shallow reflection seismic and resistivity measurements. The purpose of the investigations was to evaluate hydrogeological properties of the fjord delta aquifers with emphasis on the possibilities of abstracting saline groundwater for use in fish farming. At Sunndalsora, reflection seismic was helpful in the mapping of the base of the aquifer. Resistivity profiles revealed both the spatial and seasonal variability of seawater intrusion. Penetration depths of ground penetrating radar (GPR-D) revealed the spatial variation of the boundary of the transition zone between saline and fresh groundwater. Maps of GPR-D can be used to indicate direction and magnitude of mean hydraulic gradients and thus to locate optimal sites for both fresh and saline groundwater abstraction. In fjord delta aquifers, both rivers and abandoned river channels constitute important groundwater divides. Optimal locations for saline groundwater abstraction wells are in areas separated from the rivers by abandoned river channels. In areas between the rivers and the abandoned river channels, groundwater abstraction will result in decreasing salinity of the water.

Geology and geomorphology of the Aurland district

This article outlines the geo-specific conditions that prevail in the catchment area of the Aurland watercourse. Special emphasis has been given to geology and geomorphology. The article also contains an assessment of the impact of hydropower development on local geo-specific conditions.