Search

Independent dating of closely-spaced moraines on the west Breiðamerkurjökull foreland is used to test the accuracy of the size frequency (SF) and largest lichen (5LL) lichenometric dating techniques. The 5LL technique derived the most accurate ages for three undated moraines within the dated sequence but growth rates and lag times produced by the two methods (5LL = 0.71 mm yr−1 and 11 years; SF = 0.64 mm yr−1 and 7 years) were not significantly different. We therefore reject previous conclusions that any one technique is demonstrably inferior to the other, at least for dating glacial landforms created over the last 130 years in SE Iceland. Comparisons of climate trends and recession rates indicate that air temperature anomalies, particularly those of the summer, are the strongest driver of glacier retreat. No clear relationship between NAO trends and glacier retreat were identified, although a positive and/or rising trend in NAO is associated with the slowing of ice retreat overall, and the marked readvances of the mid-1950s, mid-1970s and mid-1990s are all coincident with positive and/or rising NAO 5yr moving averages. Summer and annual temperature trends, not the NAO, clearly show that recent accelerated global warming is driving the marked recession of the period 1995–2015. Over the last 100 years temperature has been the major driver of glacier terminus oscillations at west Breiðamerkurjökull but it is clear that extreme decreases in winter precipitation (i.e. 1960–1973) have the potential to increase retreat rates significantly even during times of below average annual temperatures. [ABSTRACT FROM AUTHOR]

Abstract: The Little Ice Age (LIA) maximum glacial extent of 13 glaciers located in SE Iceland was dated by lichenometry to check for intraregional variations. Different lichenometric approaches were applied to date maximum LIA moraines, and they all showed high variability between glaciers. According to the Extreme Value Theory and Bayesian approach, LIA advances in the region occurred in or around A.D. 1740–1760, A.D. 1810–1820 and A.D. 1840–1880 with confidence intervals of between 8 and 21 years. The dates were correlated with geomorphic characteristics of glacier tongues: hypsometric and slope parameters can be considered as determining factors in the variability of glacier timing during the LIA, as previously observed in Norway and in the Alps. In terms of timing, results obtained in SE Iceland were similar to those obtained for other glacier regions around the North Atlantic. [Copyright &y& Elsevier]

Debris flows in the Gleivarhjalli area in northwestern Iceland occurred after a sudden and intensive snowmelt period during 10–12 June, 1999. The area, in the northwestern part of the town of Ísafjörvur, was chosen for a detailed study. Meteorological data and bedrock conditions, triggering mechanisms and geomorphological and human impacts were examined. This paper describes and emphasises the role of rapid snowmelt as a mechanism for the release of debris flows in a subpolar basaltic fjord setting. Post-event mapping of erosional and depositional landforms showed strong geomorphic impacts of debris flows and their role in mass transfer in a mountainous environment. The estimated denudation rate for the singleevent is 0.29 mm/km2. The use of a new lichen growth curve provides relative dating of previous unreported events. Finally, the paper estimates the mean return period for debris-flow events in the Gleivarhjalli area as 4–5 years, thus constituting a serious threat to the community. [ABSTRACT FROM AUTHOR]

Little Ice Age (LIA) moraines along the margins of Skálafellsjökull and Heinabergsjökull, two neighbouring outlet glaciers flowing from the Vatnajökull ice-cap, have been re-dated to test the reliability of different lichenometric approaches. During 2003, 12 000 lichens were measured on 40 moraine fragments at Skálafellsjökull and Heinabergsjökull to provide surface age proxies. The results are revealing. Depending on the chosen method of analysis, Skálafellsjökull either reached its LIA maximum in the early 19th century (population gradient) or the late 19th century (average of five largest lichens), whereas the LIA maximum of Heinabergsjökull occurred by the mid-19th century (population gradient) or late-19th century (average of 5 largest lichens). Discrepancies (c. 80 years for Skálafellsjökull and c. 40 years for Heinabergsjökull) suggest that the previously cited AD 1887 LIA maxima for both glaciers should be reassessed. Dates predicted by the lichen population gradient method appear to be the most appropriate, as mounting evidence from other geochronological reconstructions and sea-ice records throughout Iceland tends to support an earlier LIA glacier maximum (late 18th to mid-19th century) and probably reflects changes in the North Atlantic Oscillation. These revised chronologies shed further light on the precise timing of the Icelandic LIA glacier maximum, whilst improving our understanding of glacier-climate interactions in the North Atlantic. [ABSTRACT FROM AUTHOR]

Abstract: The validity of the generalized extreme value method and the Bayesian approach, used by Chenet et al. (2010) in lichenometric dating of the outermost LIA Fláajökull moraines in SE Iceland, is questioned. The technique produced the date of A.D. 1821 for the abandonment of the moraine which does not agree with historical data nor does it correlate with the hypsometry (size, equilibrium line altitude and slope) of the glacier. On the other hand, a simple technique based on the five largest thalli or the size–frequency-based analysis agree well with the historical data and show that the Little Ice Age glacier maximum occurred in the late nineteenth century. [Copyright &y& Elsevier]

Abstract: In a commentary about the paper ‛Asynchronous Little Ice Age glacial maximum extent in southeast Iceland’ (Geomorphology 114 (2010) 253-260), M. Dąbski questioned the validity of the generalized extreme value method and the Bayesian approach in lichenometric dating of the outermost LIA Fláajökull moraines in SE Iceland. This paper responds to these criticisms by explaining the relevance of the method applied and the relevance of the dates obtained. [Copyright &y& Elsevier]