Do the anomalous fluctuations of Sólheimajökull reflect ice-divide migration?

Ice-divide migration may explain the pattern of Holocene glacier fluctuations around the Mýrdalsjökull ice cap in southern Iceland. On at least three occasions Sölheimajokull, the principal outlet glacier on the southwest flank of the ice cap, has exceeded the Little Ice Age limits of recent centuries that mark the maximum extent of neighbouring glaciers in the Holocene. Bedrock divides beneath the Mýrdalsjökull ice cap do not coincide with present ice divides. It is suggested that the ice divide migrated during the course of ice-cap growth. At various stages during the Holocene (7000-4500, c. 3100, 1400-1200 BP) Sólheimajokull could have drained more of the ice cap than today, so becoming more advanced than neighbouring glaciers. In the Little Ice Age ( c. AD 1600–1900) the glacier could have had a smaller catchment as a result of ice-divide migration, resulting in a more inhibited advance compared with neighbouring glaciers which reached their Holocene maximum at that time. Identification of ice-divide migration is important for palaeoclimatic reconstructions because of the need to recognize different responses of glaciers to climate if one is to use their fluctuations as indicators of change.     

Flash flood at Slheimajkull heralds the reawakening of an Icelandic subglacial volcano

An unpredicted sudden outburst flood from Sólheimajökull, Southern Iceland, in July 1999 may herald a major subglacial volcanic eruption beneath Mýrdalsjökull ice cap.     

Geomorphic evidence for Holocene glacial advances and sea level fluctuations on eastern Vestfirðir, northwest Iceland

New geomorphic and chronological data of Holocene advances of the Drangajökull Ice Cap, located on eastern Vestfirðir, northwest Iceland, are presented. At least two glacial advances and two transgressions during the Holocene are interpreted from moraines and raised beach deposits, respectively. Geomorphic evidence is concentrated in the three valleys adjacent to the modern outlet glaciers of the Drangajökull Ice Cap: Kaldalónsjökull, Leirufjarðarjökull, and Reykjarfjarðarjökull. The valley surrounding Kaldalónsjökull contains a vegetated Holocene moraine with a minimum radiocarbon age of ∼2600 cal. yr BP, which provides geomorphic evidence for Neoglacial activity on eastern Vestfirðir. The second extensive Holocene glacial advance on eastern Vestfirðir occurred during the Little Ice Age, and moraines associated with this advance are present in all three outlet glacier valleys. The Neoglacial advance is the most extensive ice advance on eastern Vestfirðir. Raised beaches parallel to the coastlines of Ísafjarðardjúp and Jökulfirðir, at an elevation of approximately 5 m a.s.l., suggest a minor transgression at ∼3000 cal. yr BP based on radiocarbon ages of shells. A minor transgression of 0.3–0.5 m a.s.l. is associated with the timing of the Little Ice Age advance. Correlation of geomorphic events with sediment proxy records facilitates distinguishing local perturbations from regional North Atlantic climate signals. This study supports regional interpretations of climatic instability during the Holocene.     

The Little Ice Age glacier maximum in Iceland and the North Atlantic Oscillation: evidence from Lambatungnajökull, southeast Iceland

This article examines the link between late Holocene fluctuations of Lambatungnajökull, an outlet glacier of the Vatnajökull ice cap in Iceland, and variations in climate. Geomorphological evidence is used to reconstruct the pattern of glacier fluctuations, while lichenometry and tephrostratigraphy are used to date glacial landforms deposited over the past ˜400 years. Moraines dated using two different lichenometric techniques indicate that the most extensive period of glacier expansion occurred shortly before c . AD 1795, probably during the 1780s. Recession over the last 200 years was punctuated by re-advances in the 1810s, 1850s, 1870s, 1890s and c . 1920, 1930 and 1965. Lambatungnajökull receded more rapidly in the 1930s and 1940s than at any other time during the last 200 years. The rate and style of glacier retreat since 1930 compare well with other similar-sized, non-surging, glaciers in southeast Iceland, suggesting that the terminus fluctuations are climatically driven. Furthermore, the pattern of glacier fluctuations over the 20th century broadly reflects the temperature oscillations recorded at nearby meteorological stations. Much of the climatic variation experienced in southern Iceland, and the glacier fluctuations that result, can be explained by secular changes in the North Atlantic Oscillation (NAO) Advances of Lambatungnajökull generally occur during prolonged periods of negative NAO index. The main implication of this work relates to the exact timing of the Little Ice Age in the Northeast Atlantic. Mounting evidence now suggests that the period between AD 1750 and 1800, rather than the late 19th century, represented the culmination of the Little Ice Age in Iceland.     

Late Quaternary glacial and climatic history of northern Cumberland Peninsula,Baffin Island,N.W.T., Canada

Radiocarbon dates on molluses in marine facies associated with glacial deposits in northern Cumberland Peninsula indicate both main fiord (Laurentide) ice and local glaciers remained at their late Wisconsin maxima until ca. 8000 BP. Essentially continuous deglaciation followed; local corrie glaciers melted out by 7100 BP and by 5500 BP fiord glaciers had receded behind the present margin of the Penny Ice Cap. The Hypsithermal warm interval probably lasted from ca. 8000 to 5000 BP. Lichenometry and radiocarbon dates on peat and buried organic horizons delimit a detailed Neoglacial chronology. Of 46 outlet and corrie glaciers investigated, the oldest Neoglacial moraines are dated lichenometrically at 3200 ± 600 BP. Subsequent advances terminated immediately prior to ca. 1650, 780, 350, and 65 yr BP, the most recent of which marked the most extensive ice coverage during the Neoglacial. The highest occurrence of lateral moraines from late Wisconsin advances of local and Laurentide ice suggest that at the late Wisconsin glacial maximum, depression of snowline varied from 450 m below present at the coast to 350 m below present level in the vicinity of the Penny Ice Cap. Moraines, surrounded by glacial ice and lying above the present steady-state ELA, suggest that during the Hypsithermal snowline was up to ca. 200 m above its present elevation. A radiometrically controlled reconstruction of relative summer paleotemperatures for the postglacial derived independently of lichenometry agrees well with the lichenometric age dating of moraines. The data suggest that between ca. 1650 and 900 BP climatic conditions were unfavorable for glacier growth, whereas the period ca. 800-65 yr BP was one of general glacial activity. During the last decade permanent snow cover has been increasing in the area. Previously reported data on climatic trends in the Canadian Arctic based on palynological analyses are similar to the chronology reported here.     

Climatic control of the surge periodicity of an Icelandic outlet glacier

Surging outlet glaciers are important in draining large ice caps, but the mechanisms controlling surge periodicities are poorly known. We investigated a sediment sequence from the glacier‐fed Lake Lögurinn in eastern Iceland, and our unique annually resolved data, based on sedimentary varves, imply that Eyjabakkajökull, an outlet glacier of Vatnajökull, began surging about 2200 cal a BP (before 1950 AD). Approximately 1700 cal a BP, the glacier started to surge at a uniform 34‐ to 38‐year periodicity that prevailed until the coldest part of the Little Ice Age when the periodicity almost halved to 21–23 years. Since the late 1800 s the surge periodicity of Eyjabakkajökull has returned to a longer period of 35–40 years. We suggest that surge periodicities of Eyjabakkajökull are forced by climatically driven mass balance changes, which may be a common forcing factor for similar surge‐type outlet glaciers. Copyright © 2011 John Wiley & Sons, Ltd.     

Glacio-tectonic structures: a mesoscale model of thin-skinned thrust sheets?

A series of seven groups of push-ridges ranging from 7 to 40 m in height, 50 to 280 m in length, and occupying a total width of more than 2 km, mark the marginal zone of the A.D. 1890 maximum of Eyjabakkajökull, an outlet glacier of the Vatnajökull ice cap, Iceland. The internal structure of one ridge complex comprises two distinct elements: a proglacial part which has been subject to compressional stresses, resulting in the development of imbricate thrust sheets; and a subglacial part which comprises low-angle normal fault structures. The two sub-systems appear to be linked via a floor thrust and to have evolved together as the glacier reached the limit of its rapid advance in A.D. 1890.     

Two millennia of glacier advances from southern Iceland dated by tephrochronology

Two glaciers at Eyjafjallajökull, south Iceland, provide a record of multiple episodes of glacier advance since the Sub-Atlantic period, ca. 2000 yr ago. A combination of tephrochronology and lichenometry was applied to date ice-marginal moraines, tills and meltwater deposits. Two glacier advances occurred before the 3rd century AD, others in the 9th and 12th centuries bracketing the Medieval Warm Period, and five groups of advances occurred between AD 1700 and 1930, within the Little Ice Age. The advances of Eyjafjallajökull before the Norse settlement (ca. AD 870) were synchronous with other glacier advances identified in Iceland. In contrast, medieval glacier advances between the 9th and 13th centuries are firmly identified for the first time in Iceland. This challenges the view of a prolonged Medieval Warm Period and supports fragmentary historical data that indicate significant medieval episodes of cooler and wetter conditions in Iceland. An extended and more detailed glacier chronology of the mid- and late Little Ice Age is established, which demonstrates that some small outlet glaciers achieved their Little Ice Age maxima around AD 1700. While Little Ice Age advances across Iceland appear to synchronous, the timing of the maximum differs between glacier type and region.     

The Skógar Tephra, a Younger Dryas marker in North Iceland

A composite stratigraphical sequence, the Fnjóskadalur Sequence, reveals ten cycles of glacier advances and formation of ice-dammed lakes in Fnjóskadalur in central North Iceland. Chemical analyses of the Skógar Tephra, with its type locality in this valley, have enabled a correlation with Ash zone I in deep sea sediments of the North Atlantic and with the Vedde Ash Bed on land in western Norway, where it is dated to 10,600 BP. The Skógar Tephra is composed of two layers, a basaltic tephra (STP-1) and a rhyolitic tephra (STP-2) erupted almost simultaneously from two different Icelandic volcanoes. The STP-1 tephra originates from the Katla volcano in South Iceland, and the öræfajökull volcano in Southeast Iceland is considered a plausible source of the STP-2 tephra. This new dating of the Skógar Tephra puts the three youngest glacier advances of the Fnjóskadalur Sequence within a 1000 year period between 10,600 and 9650 BP. The redated Late Weichselian glacial history now extracted from the Fnjóskadalur Sequence shows that glaciers in North Iceland were more extended in Younger Dryas and Preboreal times than previously assumed. This fits with the revised deglaciation pattern which has evolved in recent years.     

Glacier fluctuations in the western Alps during the Neoglacial,as indicated by the Miage morainic amphitheatre (Mont Blanc massif,Italy)

Holocene glacier variations pre‐dating the Little Ice Age are poorly known in the western Alps. Studied for two centuries, the Miage morainic amphitheatre (MMA) is composed of three subconcentric sets of c. 25 moraines. Because of its location and of a dominant mode of morainic accretion, the MMA is a well‐preserved marker of the glacier dynamics during the Neoglacial. Radiocarbon dates were obtained by digging and coring in inter‐ morainic depressions of the MMA and through a deep core drilling in a dammed‐lake infill (Combal); complementary data for the inner MMA were obtained by lichenometry and dendrochronology. Radiocarbon chronology shows that (i) the MMA not only pre‐dates the Little Ice Age (LIA), but was built at least since 5029–4648 cal. yr BP (beginning of the Neoglacial); (ii) outer sets of moraines pre‐date 2748–2362 cal. yr BP; (iii) the MMA dammed the Lake Combal from 4.8 to 1.5 cal. kyr BP, while lakes/ponds formed inside the moraines (e.g. from 2147–1928 to 1506–1295 cal. yr BP). The ‘Neoglacial model’ proposed here considers that the MMA formed during the whole Neoglacial by a succession of glacier advances at 4.8–4.6 cal. ky BP (early Neoglacial), around 2.5 cal. ky BP (end of Göschener I), at AD 600–900 (end of Göschener II) and during the LIA, separated by raising phases of the right‐lateral moraine by active dumping because of the Miage debris cover.     

The rapid deglaciation of the Skagafjörður fjord,northern Iceland

The Skagafjörður fjord in northern Iceland is located between the Tröllaskagi Peninsula in the east and the Skagi Peninsula in the west. The tributary valleys of the fjord originate in the highland area about 15 km north of the Hofsjökull icecap. The results of this work improve the knowledge of the deglaciation pattern in Skagafjörður and explore the adequacy of the ³⁶Cl cosmic ray exposure dating method in an Icelandic environment, where this method has rarely been applied to deglaciated surfaces. The ³⁶Cl dating method was applied to 13 rock samples taken on a transect from the coastal areas towards the highlands. All samples were obtained from rock outcrops with glacier‐polished surfaces from the Last Glaciation and from one of the few well‐preserved erratic boulders. The cosmogenic results, combined with previous radiocarbon results, indicate that the ice margin was situated in the outermost sector of Skagafjörður at approximately 17–15 ka BP. Subsequently, it retreated and occupied the central part of the fjord between 15 and 12 ka BP and then the innermost sector of the fjord about 11 ka BP. The samples collected between this position and the highlands show an average age of approximately 11 ka, indicating rapid deglaciation after the early Preboreal. These results agree with earlier studies of the deglaciation history of northern Iceland, reinforce previous deglaciation models in the area and enable a better understanding of glacial evolution in the North Atlantic from the Late Pleistocene to Holocene transition.     

Fluvial adjustments in response to glacier retreat: Skaftafellsjökull,Iceland

This study describes changes to the proglacial drainage network of Skaftafellsjökull, Iceland from 1998 to 2011. Proglacial landscapes are highly sensitive to glacier retreat, and the retreat of glaciers around the world has accelerated since the mid‐1990s. Skaftafellsjökull has retreated at an average rate of 53 m per year since 1999. From 1999 to 2003, the river incised and formed a sequence of now abandoned channels and fluvial terraces extending ～1 km downstream from the glacier. Retreat of the glacier from an over‐deepened ice‐contact slope meant that there was a positive correlation between the distance of glacier retreat and the amount of fluvial incision. Incision was episodic, occurring annually in response to drainage reactivation and reorganization. On an annual basis, the rate of retreat is moderately negatively correlated with the rate of incision. This is partly because the ice‐contact slope decreases away from the position of maximum glacier extent, and also because more sediment is released with faster retreat, counteracting the effect of retreat down an ice‐contact slope. From 2003 onwards, proximal terrace formation ceased, as a proglacial lake became established. Downstream of the lake outlet further incision deepened the channel, with most change occurring during a flood in 2006, where incision in the upstream confined reach was accompanied by downstream aggradation and terrace formation. These observations indicate that proglacial changes in response to glacier retreat are a result of the interactions of river channel incision and terrace formation, aggradation, lake development, and flooding, which together control river channel changes, sediment redistribution and sandur stratigraphy.     

Landsystems of Morsárjökull,Skaftafellsjökull and Svínafellsjökull,outlet glaciers of the Vatnajökull Ice Cap,Iceland

This study utilizes a landsystem approach to analyse the landforms and sediments exposed on the forefields of three closely spaced outlet glaciers of the Vatnajökull Ice Cap, southeast Iceland; Morsárjökull, Skaftafellsjökull and Svínafellsjökull, in order to determine how individual glacier and environmental characteristics influence landscape development. Analysis of satellite imagery and fieldwork were used in conjunction to examine the geomorphology and sedimentology of the forefields, and to define the characteristic landsystems of each of the glaciers. Morsárjökull and Skaftafellsjökull have similar proglacial fields, with similarities in the distribution and scale of the landforms, and their characteristics conform to the established active temperate landsystem. Svínafellsjökull differs significantly from the other glaciers having a proglacial field that more closely resembles an early stage debris‐charged landsystem. Variations between the glaciers in terms of their ice distribution (hypsometry, equilibrium line altitude), bedrock type, topography and debris content are important factors that contribute to the landsystem variability evident in their proglacial fields. The forefields of these three glaciers may be used as analogues to enhance understanding of palaeoenvironmental conditions that existed along the southern margin of Pleistocene glaciers that covered much of northern North America and Europe in the past.     

Holocene climate and glacial history of the northeastern Antarctic Peninsula: the marine sedimentary record from a long SHALDRIL core

A high-resolution record of Holocene deglacial and climate history was obtained from a 77 m sediment core from the Firth of Tay, Antarctic Peninsula, as part of the SHALDRIL initiative. This study provides a detailed sedimentological record of Holocene paleoclimate and glacial advance and retreat from the eastern side of the peninsula. A robust chronostratigraphy was derived from thirty-three radiocarbon dates on carbonate material. This chronostratigraphic framework was used to establish the timing of glacial and climate events derived from multiple proxies including: magnetic susceptibility, electric resistivity, porosity, ice-rafted debris content, organic carbon content, nitrogen content, biogenic silica content, and diatom and foraminiferal assemblages. The core bottomed-out in a stiff diamicton interpreted as till. Gravelly and sandy mud above the till is interpreted as proximal glaciomarine sediment that represents decoupling of the glacier from the seafloor circa 9400 cal. yr BP and its subsequent landward retreat. This was approximately 5000 yr later than in the Bransfield Basin and South Shetland Islands, on the western side of the peninsula. The Firth of Tay core site remained in a proximal glaciomarine setting until 8300 cal. yr BP, at which time significant glacial retreat took place. Deposition of diatomaceous glaciomarine sediments after 8300 cal. yr BP indicates that an ice shelf has not existed in the area since this time.The onset of seasonally open marine conditions between 7800 and 6000 cal. yr BP followed the deglacial period and is interpreted as the mid-Holocene Climatic Optimum. Open marine conditions lasted until present, with a minor cooling having occurred between 6000 and 4500 cal. yr BP and a period of minor glacial retreat and/or decreased sea ice coverage between 4500 and 3500 cal. yr BP. Finally, climatic cooling and variable sea ice cover occurred from 3500 cal. yr BP to near present and it is interpreted as being part of the Neoglacial. The onset of the Neoglacial appears to have occurred earlier in the Firth of Tay than on the western side of the Antarctic Peninsula. The Medieval Warm Period and Little Ice Age were not pronounced in the Firth of Tay. The breadth and synchroneity of the rapid regional warming and glacial retreat observed in the Antarctic Peninsula during the last century appear to be unprecedented during the Holocene epoch.     

Sedimentation and stratigraphy at Eyjabakkajökull—An Icelandic surging glacier

A model for sedimentation by surging glaciers is developed from analysis of the debris load, sedimentary processes, and proglacial stratigraphy observed at the Icelandic surging glacier, Eyjabakkajökull. Three aspects of the behavior of surging glaciers explain the distinctive landformsediment associations which they may produce: (a) sudden loading of proglacial sediments during rapid glacier advances results in the buildup of excess pore pressures, failure, and glacitectonic deformation of the overridden sediments; (b) reactivation of stagnant marginal ice by the downglacier propagation of surges is associated with large longitudinal compressive stresses. These induce intense folding and thrusting during which basal debris-rich ice is elevated into an englacial position in a narrow marginal zone. As the terminal area of the glacier stagnates between surges, debris from this ice is released supraglacially and deposited by meltout and sediment flows; (c) local variations in overburden pressure beneath stagnant, crevassed ice cause subglacial lodgement tills, which are sheared during surges, to flow into open crevasses and form “crevasse-fill” ridges.     

Ice-flow patterns and dispersal of erratics at the southwestern margin of the last Scandinavian Ice Sheet: signature of palaeo-ice streams

An extensive set of proxy-data was acquired from eastern and central Denmark in order to study the dynamic behaviour of the southwestern margin of the last Scandinavian Ice Sheet. We examine the last three glacier advances of the Late Weichselian: the Main advance from central Sweden, representing the maximum ice extent at this time ( c. 21–20 ka BP), and the two succeeding Baltic advances ( c. 18–15 ka BP). Directional properties from tills and glaciotectonic overprints are used to reveal large-scale flowline patterns. Together with the geomorphological outline of ice margins, flowlines were successively more fan-shaped, indicating that the dependence of the subglacial topography increases as ice advances become younger. It is suggested that while the ice thickness decreases, more lobate configurations of ice margins are created as a result. Clast-compositional data derived from the fine-gravel fraction in tills are used to reconstruct dispersal patterns of erratic material. The dispersal patterns during the three advances show a gradually diminishing influence of local Pre-Quaternary bedrocks and older glacial deposits, and progressively longer transport distances of far-travelled erratics. We speculate that the principal factor governing this development is a successively decreasing interaction between the ice and its bed, which influences the concentration of erratics, debris comminution processes and the basal ice velocity. We envisage the Main advance from central Sweden as a slow-flowing inter-stream ice body with high bed interaction compared to the succeeding Baltic advances, which we regard to have been rapid flowing ice streams with limited bed interaction.     

Holocene and latest Pleistocene climate and glacier fluctuations in Iceland

Multiproxy climate records from Iceland document complex changes in terrestrial climate and glacier fluctuations through the Holocene, revealing some coherent patterns of change as well as significant spatial variability. Most studies on the Last Glacial Maximum and subsequent deglaciation reveal a dynamic Iceland Ice Sheet (IIS) that responded abruptly to changes in ocean currents and sea level. The IIS broke up catastrophically around 15 ka as the Polar Front migrated northward and sea level rose. Indications of regional advance or halt of the glaciers are seen in late Alleröd/early Younger Dryas time and again in PreBoreal time. Due to the apparent rise of relative sea level in Iceland during this time, most sites contain evidence for fluctuating, tidewater glacier termini occupying paleo fjords and bays. The time between the end of the Younger Dryas and the Preboreal was characterized by repeated jökulhlaups that eroded glacial deposits. By 10.3 ka, the main ice sheet was in rapid retreat across the highlands of Iceland. The Holocene thermal maximum (HTM) was reached after 8 ka with land temperatures estimated to be 3 °C higher than the 1961–1990 reference, and net precipitation similar to modern. Such temperatures imply largely ice-free conditions across Iceland in the early to mid-Holocene. Several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8.5 and 8 ka, but no moraines have been detected from that time. Termination of the HTM and onset of Neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4.5 and 4.0 ka, intensifying between 3.0 and 2.5 ka. Although a distinct warming during the Medieval Warm Period is not dramatically apparent in Icelandic records, the interval from ca AD 0 to 1200 is commonly characterized by relative stability with slow rates of change. The literature most commonly describes Little Ice Age moraines (ca AD 1250–1900) as representing the most extensive ice margins since early Holocene deglaciation, with temperature depressions of 1–2 °C compared to the AD 1961–1990 average. Steep north–south and west–east temperature gradients are reconstructed in the Holocene records of Iceland, suggesting a strong maritime influence on the terrestrial climate of Iceland.     

Late Quaternary history of Washington Land, North Greenland

During the last glacial stage, Washington Land in western North Greenland was probably completely inundated by the Greenland Ice Sheet. The oldest shell dates from raised marine deposits that provide minimum ages for the last deglaciation are 9300 cal. yr BP (northern Washington Land) and 7600 cal. yr BP (SW Washington Land). These dates indicate that Washington Land, which borders the central part of Nares Strait separating Greenland from Ellesmere Island in Canada, did not become free of glacier ice until well into the Holocene. The elevation of the marine limit falls from 110 m a.s.l. in the north to 60 m a.s.l. in the southwest. The recession was followed by readvance of glaciers in the late Holocene, and the youngest shell date from Neoglacial lateral moraines north of Humboldt Gletscher is 600 cal. yr BP. Since the Neoglacial maximum, probably around 100 years ago, glaciers have receded. The Holocene marine assemblages comprise a few southern extralimital records, notably of Chlamys islandica dated to 7300 cal. yr BP. Musk ox and reindeer disappeared from Washington Land recently, perhaps in connection with the cold period that culminated about 100 years ago.     

The age and origin of Neoglacial moraines in Jotunheimen, southern Norway: new evidence from weathering-based data

This paper considers the controversial issue of the existence of pre-'Little Ice Age' Neoglacial moraines in southern Norway. Schmidt hammer rebound values are combined with measures of boulder roundness and weathering rind thickness in an attempt to isolate moraines that include weathered boulders. A critical approach is used in distinguishing sites where boulders have weathered in situ from those where previously weathered clasts have been incorporated into relatively young moraines. The results confirm that possible pre-'Little Ice Age' Neoglacial moraines seem to be restricted to small, high-altitude glaciers in eastern Jotunheimen. It is concluded that at these glaciers a particularly large response to a short-lived earlier Holocene climatic event is more likely to explain the survival of such moraines than a particularly subdued response to the climatic deterioration of the 'Little Ice Age'. More refined dating techniques are required to determine the age of formation of the anomalous moraines, but before the palaeoclimatic significance of such dates can be assessed, a critical test is required to establish whether the moraines mark former ice-front positions, and therefore reflect lowering of equilibrium line altitudes, or whether they have been displaced forwards by later and more extensive glacier advances.     

Glacier margin fluctuations, Skaftafellsjökull, Iceland: implications for sandur evolution

This paper relates recent proglacial fluvial channel change at Skaftafellsjökull, southeast Iceland, to glacier margin fluctuations. Observations of the western portion of the proglacial braided sandur were made annually between 1996 and 2000. Between 1996 and 1998, during a period of glacier advance, the proximal proglacial outwash surface at the western end of the glacier margin was characterized by a complex braided channel pattern active over the entire sandur surface. Retreat of the glacier margin since 1998 led to rapid incision, so that by 1999 abandonment of the proximal terrace surface and reorganization of the proglacial fluvial system into a single, entrenched channel had occurred. Further retreat and incision occurred during 1999–2000. These observations demonstrate that glacier retreat at Skaftafellsjökull is accompanied by short-lived rapid incision events and terrace formation, separated by long intervals of relatively minor change rather than progressive incision over long time periods. The margin of Skaftafellsjökull is thought to be particularly sensitive to retreat, as the glacier occupies an overdeepening behind the snout and results in lowering of the river's point of exit from the glacier, necessitating adjustment of the river's long profile.