Jökull


Jökull - 01.01.2020, Page 28

Jökull - 01.01.2020, Page 28
Glacier extent in Iceland, 1890–2019 Figure 13: Area (with respect to the maximum LIA extent) of the main Icelandic ice caps and all the glaciers in total since the end of the 19th century. Open circles denote additional data points that are not derived from outlines in the GLIMS data set (see caption of Figure 12). The step rise in the curves for Vatnajökull and all glaciers is due to the surge in Brúar- jökull in 1963–1964. The left y-axis applies to the area of Vatnajökull (V) and all glaciers (blue line), whereas the right y-axis applies to the smaller ice caps (L=Langjökull, H=Hofsjökull, M=Mýrdalsjökull). – Flatarmál meginjökla landsins og einnig allra jökla landsins samtals. Skyndileg aukning í flatarmáli Vatnajökuls árið 1964 kemur til vegna framhlaups Brúarjökuls 1963–1964. Vinstri y-ásinn á við Vatnajökul og alla jökla (blá lína), en hægri y-ás á við Langjökul, Hofsjökul og Mýrdalsjökul. varies between −7.2 km2 a−1 (∼1973 to ∼2000) and −44 km2 a−1 (∼2010 to ∼2014). The rate of rela- tive area change is in general inversely related to the size of the glacier. It is greatest in magnitude for the smaller intermediate-size glaciers (3–10 km2) and varies between −0.37 % a−1 (∼1945 to ∼1973) and −2.5 % a−1 (∼2010 to 2014). This may for example be compared with −0.07 % a−1 (in ∼1945 to 1973) and −0.52 % a−1 (∼2010 to 2014) for Hofsjökull. DISCUSSION The general pattern of glacier area changes reflects the fluctuations in the climate in Iceland since the end of the 19th century, as seen in variation in the sum- mer temperature in Stykkishólmur (Figure 2), with occasional exceptions due to surges. This temperature record may be considered representative of the rather spatially uniform decadal temperature variations in Iceland (Crochet, 2011), in agreement with model studies of the response of Icelandic glaciers to climate variations (Aðalgeirsdóttir et al., 2011; Flowers et al., 2007, 2008; Schmidt et al., 2017). Areal changes are not an unequivocal indicator of climate changes, as glacier response to climate change depends on sev- eral non-climatic factors. But area changes are more easily extracted from various remote sensing data and historical information about glacier variations than glaciological or geodetic mass balance. Information about variations in glacier extent can be useful to complement available data about mass-balance vari- ations in analyses of glacier–climate interactions, and past changes in ice volumes can be derived from glacier extent variations with the volume–area scal- ing method (Bahr et al., 2015; Aðalgeirsdóttir et al., 2020). Glacier-area changes and outlet-length variations are related, as the main area changes generally take place in the ablation area. The terminus variation measurements of the Iceland Glaciological Society (collected since the 1930s, see spordakost.jorfi.is) re- flect the general pattern of area changes of glaciers in Iceland. The in-situ length-change observations JÖKULL No. 70, 2020 25
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