Shrinkages and surges of Drangajökull since 1850

This is a very useful publication.  Note that a very large shrinkage of the ice cap is shown for the southern sector, and for a large dome on the western flank, between Kaldalon and Leirufjördur.  Recent studies suggest that these areas may not have supported moving glacier ice after 1850 -- it is suggested that there were simply extensive snowfields and firn accumulations which were never thick enough to be transformed into glacier ice. 

I see a possible parallel here in the UK, during the Devensian, with connected snowfields between actual ice masses in small ice caps on Dartmoor, Exmoor, Bodmin, Mendip etc..........

 https://jokull.jorfi.is/articles/jokull2020.70/jokull2020.70.001.pdf

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It is now also widely accepted that all three of the main outlet glaciers of Drangajökull are subject to surging behaviour, somewhat out of sync with the other (larger) ice masses of Iceland.  Each surge appears to last for up to ten years -- significantly longer than the surges of the larger glaciers of Iceland.

See also:

Brynjólfsson, S., A. Schomacker, E. R. Guðmundsdóttir and Ó. Ingólfsson. 2015. A 300-year surge his- tory of the Drangajökull ice cap, northwest Ice- land, and its maximum during the ”Little Ice Age”. Holocene 25(7), 1076–1092. http://doi.org/10.1177/- 0959683615576232

Harning, D. J., Á. Geirsdóttir, G. H. Miller and L. Anderson 2016. Episodic expansion of Drangajökull, Vestfirðir, Iceland, over the last 3 ka culminating in its maximum dimension during the Little Ice Age. Quat. Sci. Rev. 152, 118–131. http://doi.org/10.1016/- j.quascirev.2016.10.001

Extract from Brynjolfsson et al, 2016:

Surges of outlet glaciers from the Drangajökull ice cap, northwest Iceland,  Earth and Planetary Science LettersVolume 450, 15 September 2016, Pages 140-151

The reason for Drangajökull outlets displaying surge behaviour so different from surging glaciers of the other Icelandic ice caps remains to be fully understood. Bedrock substrate or flow rate has hitherto not been considered obvious variables controlling surge frequencies during the surge phase of Icelandic surge-type glaciers, although Brynjólfsson et al. (2015a) suggested it could not be excluded that the Miocene basalts below Drangajökull, which are different from the predominantly Pliocene–Pleistocene bedrock of other Icelandic ice caps, could at least partly explain the surge behaviour. Svalbard surging glaciers, recently suggested to be over 700 in number (Farnsworth et al., 2016), do occur on a variety of subglacial lithologies, from igneous and metamorphic Precambrian–Paleozoic basement rocks to sedimentary and igneous rocks of Paleozoic–Cenozoic age (Jiskoot et al., 1998, Murray et al., 2003, Farnsworth et al., 2016), but generally share the characteristics of long surge cycles and duration of the active surge phase. The geothermal heat flux below Drangajökull is comparable to the heat flux below Brúarjökull and Múlajökull (a very active surging outlet of Hofsjökull), estimated to be between 100–200 mW/m2 (Hjartarsson, 2015), so that the very different surge dynamics and kinematics can probably not be explained by differences in geothermal heat flux. Recent studies of Drangajökull have focused on geomorphology, glacial history since the Last Glacial Maximum (LGM), surge dynamics and recent areal changes of the ice cap (Principato, 2003, Principato, 2008, Principato et al., 2006, Þrastarson, 2006, Brynjólfsson et al., 2014, Brynjólfsson et al., 2015a, Brynjólfsson et al., 2015b). Differencing of Digital Elevation Models (DEMs) is a well-established methodology to quantify volume changes of glaciers (e.g., Magnússon et al., 2005, Magnússon et al., 2015, Schomacker and Kjær, 2007, Schomacker and Kjær, 2008, Sund et al., 2009, Sund et al., 2014, Abermann et al., 2010, Kjær et al., 2012, Schomacker et al., 2012, Jóhannesson et al., 2013). Time series of DEMs and other remotely sensed data are also commonly used to identify glacier surges and quantify their velocity, surface, volume and areal changes during the surges (Fischer et al., 2003, Magnússon et al., 2005, Magnússon et al., 2015, Frappé and Clarke, 2007, Sund et al., 2009, Sund et al., 2014, Quincey et al., 2011).
Shuman et al. (2009) compared a GPS derived Digital Elevation Model (DEM) with series of repeated satellite profiles across Drangajökull, indicating up to 1.5 m a−1 surface lowering at the location of the satellite profile in the years 2003–2007. However, ablation stake measurements indicate positive mass balance of the whole ice cap in 2005–2007, indicating that the satellite profile is not representative for the whole ice cap (Shuman et al., 2009).

Comparison of DEMs since c. 1990 and from 2011, indicates about 8 m average surface lowering of the ice cap in the period 1990–2011 (Jóhannesson et al., 2013). Obvious ice discharges during the most recent surges of the three outlet glaciers are reflected as much more thinning of their reservoirs and distinct thickening of the receiving areas of each outlet glacier as described by Jóhannesson et al. (2013). Recently, Magnússon et al. (2015) calculated the geodetic mass balance of Drangajökull in six time steps back to 1946 based on DEMs from aerial photographs. They demonstrated a mean mass balance rate of the ice cap of in the period 1946–2011. However, they also observed high decadal variability in the mass balance with, e.g., a positive mass balance rate of in 1975–1985 and from 1985–1994. Thus, the mass balance of Drangajökull does not appear to follow exactly the increasing temperature trend in the Arctic (Miller et al., 2010). However, on longer timescales, Drangajökull is thinning and its surface area has decreased since the LIA and during the last decades (Jóhannesson et al., 2013, Brynjólfsson et al., 2014, Brynjólfsson et al., 2015a, Magnússon et al., 2015).

The aim of this study is to quantify the ice elevation and volume changes related to the most recent surges (1994–2006) of the three major outlet glaciers of Drangajökull ice cap. Furthermore, we analyse the characteristics of Drangajökull surges and discuss their distinct difference from surges from the other Icelandic ice caps.

Setting
The Drangajökull ice cap is located c. 100–915 m above sea level (a.s.l.) on the eastern Vestfirðir (Westfjords) peninsula in northwest Iceland (Fig. 1). Since the LIA, the glaciated area has decreased from about 190–216 km2(Sigurðsson et al., 2013, Brynjólfsson et al., 2015a) to 142 km2 in 2011 (Jóhannesson et al., 2013). Drangajökull is located at the gateway to the Arctic, where the relatively warm Irminger branch of the North Atlantic Current and the cold East Greenland Current meet, and
Aerial photographs and Digital Elevation Models

Two sets of aerial stereo-photographs and derived DEMs from 1994 and 2005 in addition to an airborne Light Detection and Ranging (LiDAR) derived DEM from 2011, were used in this study (Table 1). The Root Mean Square Error (RMSE) of the DEMs (Table 1) is used to assign uncertainty in the elevation measurements. The 1994 aerial photographs were supplied by the National Land Survey of Iceland (Landmælingar Íslands). Orthorectified aerial photographs and a DEM with 5 m ground resolution were
Ice surface and volume changes 1994–2011

The three individual DEMs (Table 1) enable calculations of ice surface and volume changes for the period 1994–2011, 1994–2005 and 2005–2011 (Table 2). Because the DEM from 1994 does not completely cover Kaldalónsjökull, or its forefield (Fig. 4), Kaldalónsjökull was mostly excluded from this study. However, according to the 1994–2011 DoD (Fig. 4) it was only the western and northwest part of Kaldalónsjökull that contributed to its last surge in 1995–1999. The 1994–2011 DoD covers 102 km2 of the Reykjarfjarðarjökull.

The nunatak, Hljóðabunga (Fig. 1 and Fig. 2), seems to have acted as a barrier for ice flow during the surge of Reykjarfjarðarjökull 2002–2006. Longitudinal fractures and folded sediment bands within the ice are visible on aerial photo and can be traced from Hljóðabunga downglacier to the margin. Thus, the surge did not affect the glacier south of Hljóðabunga during the recent most surge in 2002–2006 (Fig. 1). GIS analysis indicates that most of the ice-volume discharge was from above the ELA

Conclusions
By using DEMs from 1994, 2005 and 2011 we have quantified ice surface elevation and volume changes that relate to the recent most surges of the surging outlet glaciers, Reykjarfjarðarjökull and Leirufjarðarjökull.

Holocene glacier and climate variations in Vestfirðir, Iceland, from the modeling of Drangajökull ice cap
2018, Quaternary Science Reviews

Citation Excerpt :

Because of the ice cap's narrow width, low surface slopes, and low maximum elevation, the rain shadow effect across Drangajökull is small (Roe and Baker, 2006), compared to the other large Icelandic ice caps (Einarsson, 1977; Crochet et al., 2007). Since 1930, the surge and outlet-length histories of Drangajökull were documented through direct observation and historical accounts (Sigurðsson, 1998; Björnsson et al., 2003; Brynjólfsson et al., 2014, 2015a; 2016; Ingólfsson et al., 2016; Magnússon et al., 2016a). Glaciers contracted since 1930, despite three outlets of Drangajökull each surging twice (Sigurðsson, 1998).

The Drangajökull ice cap, northwest Iceland, persisted into the early-mid Holocene
2016, Quaternary Science Reviews

Citation Excerpt :

Recently, Brynjólfsson et al. (2014, 2015a, b) outlined the history of Drangajökull outlets since the Little Ice Age as well as highlighting the surge-type outlet glacier dynamics. Brynjólfsson et al. (2014, 2016) and Ingólfsson et al. (2016) pointed out that the Drangajökull surge-type glaciers behaved more like the polythermal Svalbard surging outlets than the warm-based surging outlets of other Icelandic ice caps. Understanding the Holocene pattern of Drangajökull’s oscillations can improve our understanding of the dynamics of Holocene environmental changes in this key area.