Spatial analysis of cirques from three regions of Iceland: implications for cirque formation and palaeoclimate

This study is a quantitative analysis of cirques in three regions of Iceland: Trollaskagi, the East Fjords and Vestfiroir. Using Google Earth and the National Land Survey of Iceland Map Viewer, we identified 347 new cirques on Trollaskagi and the East Fjords region, and combined these data with 100 cirques previously identified on Vestfiroir. We used ArcGIS to measure length, width, aspect, latitude and distance to coastline of each cirque. Palaeo-equilibrium-line altitudes (palaeo-ELAs) of palaeo-cirque glaciers were calculated using the altitude-ratio method, cirque-floor method and minimum-point method. The mean palaeo-ELA values in Trollaskagi, the East Fjords and Vestfiroir are 788, 643 and 408m a.s.l, respectively. Interpolation maps of palaeo-ELAs demonstrate a positive relationship between palaeo-ELA and distance to coastline. A positive relationship between palaeo-ELA and latitude is observed on Vestfiroir, a negative relationship is observed on Trollaskagi and no statistically significant relationship is present on the East Fjords. The modal orientation of cirques on Trollaskagi and Vestfiroir is northeast, while orientation of cirques in the East Fjords is north. Palaeo-wind reconstructions for the LGM show that modal aspect isaligned with the prevailing north-northeast wind directions, although aspect measurements demonstrate wide dispersion. Cirque length is similar on Trollaskagi and the East Fjords, but cirques are approximately 200m shorter in Vestfiroir. Cirque widths are similar in all three regions. Comparisons with a global data set show that cirques in Iceland are smaller and more circular than cirques in other regions of the world. Similar to glaciers in Norway and Kamchatka, our results demonstrate that access to a moisture source is a key parameter in determining palaeo-ELAs in Iceland. Temperatures interpreted from palaeo-ELA depressions suggest that these cirques may have been glaciated as recently as the Little Ice Age.