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Response of Eyjafjallajo¨ Kull, Torfajo¨ Kull and Tindfjallajo¨ Kull Ice Caps In

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Response of Eyjafjallajo¨ Kull, Torfajo¨ Kull and Tindfjallajo¨ Kull Ice Caps In RESEARCH/REVIEW ARTICLE Response of Eyjafjallajo¨ kull, Torfajo¨ kull and Tindfjallajo¨ kull ice caps in Iceland to regional warming, deduced by remote sensing Sverrir Gudmundsson,1 Helgi Bjo¨ rnsson,1 Eyjo´ lfur Magnu´ sson,1 Etienne Berthier,2 Finnur Pa´ lsson,1 Magnu´ s Tumi Gudmundsson,1 Tho´ rdı´s Ho¨ gnado´ ttir1 & Jørgen Dall3 1 Institute of Earth Sciences, University of Iceland, Sturlugata 7, Askja, Reykjavı´k IS-101, Iceland 2 Centre National de la Recherche Scientifique, Universite´ de Toulouse, Laboratoire d’Etudes en Ge´ ophysique et Oce´ anographie Spatiale, Universite´ de Toulouse, 14 Avenue Edouard Belin, Toulouse FR-31400, France 3 National Space Institute, Technical University of Denmark, Lyngby DK-2800, Denmark Keywords Abstract Remote sensing; glacier mass balance; regional warming; Eyjafjallajo¨ kull; We assess the volume change and mass balance of three ice caps in southern Torfajo¨ kull; Tindfjallajo¨ kull. Iceland for two periods, 1979Á1984 to 1998 and 1998 to 2004, by comparing digital elevation models (DEMs). The ice caps are Eyjafjallajo¨ kull (ca. 81 km2), Correspondence Tindfjallajo¨kull (ca. 15 km2) and Torfajo¨kull (ca. 14 km2). The DEMs were Sverrir Gudmundsson, Institute of Earth compiled using aerial photographs from 1979 to 1984, airborne Synthetic Sciences, University of Iceland, Sturlugata Aperture Radar (SAR) images obtained in 1998 and two image pairs from the 7, Askja, Reykjavı´k IS-101, Iceland. E-mail [email protected] SPOT 5 satellite’s high-resolution stereoscopic (HRS) instrument acquired in 2004. The ice-free part of the accurate DEM from 1998 was used as a reference map for co-registration and correction of the vertical offset of the other DEMs. The average specific mass balance was estimated from the mean elevation difference between glaciated areas of the DEMs. The glacier mass balance declined significantly between the two periods: from 0.2 to 0.2 m yr1 w. eq. during the earlier period (1980s through 1998) to 1.8 to 1.5 m yr1 w. eq. for the more recent period (1998Á2004). The declin- ing mass balance is consistent with increased temperature over the two periods. The low mass balance and the small accumulation area ratio of Tindfjallajo¨kull and Torfajo¨ kull indicate that they will disappear if the present- day climate continues. The future lowering rate of Eyjafjallajo¨ kull will, however, be influenced by the 2010 subglacial eruption in the Eyjafjallajo¨ kull volcano. Iceland is located in the North Atlantic Ocean (Fig. 1), runoff are important for the design and operation of at the confluence of air/water masses from the mid- power plants as well as for the constructions of roads and latitudes and from the Arctic. About 11% of Iceland is bridges. covered by glaciers, all of which are temperate, have a Icelandic glaciers are currently melting at a fast high annual mass turnover and are highly sensitive to rate. Over recent decades, annual mass balance field climate fluctuations (e.g., Bjo¨ rnsson 1979; Bjo¨ rnsson & observations on the three largest ice caps in Iceland* Pa´lsson 2008). Glacier meltwater is mainly delivered Langjo¨ kull (ca. 900 km2), Hofsjo¨ kull (ca. 890 km2) and directly to rivers but in places considerable volumes are Vatnajo¨kull (ca. 8100 km2)*show a declining specific delivered to groundwater aquifers. Glacier river discharge mass balance from about 0 m yr1 w. eq. on average provides a significant portion of the river water that is from 1980 to 1994 to 1to1.3 m yr1 w. eq. on harnessed by hydroelectric power plants. Changes in average after 1995 (Bjo¨rnsson et al. 2002; Sigurdsson Polar Research 2011. # 2011 S. Gudmundsson et al. This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial 3.0 1 Unported License (http://creativecommons.org/licenses/by-nc/3.0/), permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Citation: Polar Research 2011, 30, 7282, DOI: 10.3402/polar.v30i0.7282 (page number not for citation purpose) Mass balance of three ice caps in southern Iceland S. Gudmundsson et al. Fig. 1 Eyjafjallajo¨ kull (E), Tindfjallajo¨ kull (Ti), Torfajo¨ kull (To) and My´ rdalsjo¨ kull (M) ice caps. The G´ıgjo¨ kull outlet glacier (G) of Eyjafjallajo¨ kull is also indicated. The inset map of Iceland shows the location of the study area as well as Langjo¨ kull (L), Hofsjo¨ kull (H) and Vatnajo¨ kull (Va) ice caps and these weather stations: Vı´k (V) in My´rdalur (15 m a.s.l., ca. 30 km south-east of Eyjafjallajo¨ kul), Hveravellir (Hv; 641 m a.s.l., ca. 100 km north of Tindfjallajo¨ kull and Torfajo¨ kull) and Ho´ lar (Ho) in Hornafjo¨ rdur (18 m a.s.l.). The plot shows the elevation distribution of the Eyjafjallajo¨ kull, Tindfjallajo¨ kull and Torfajo¨ kull ice caps as area (km2) per 10 m elevation interval. et al. 2004; Pa´lsson et al. 2007; Bjo¨ rnsson & Pa´lsson 2008; This approach provides results over large areas in cont- Gudmundsson et al. 2009). This is consistent with the rast to the few points that traditional mass balance warming in Iceland that has taken place since 1994 (e.g., observations yield. Bjo¨ rnsson et al. 2005; Jo´ hannesson et al. 2007). Model- In this paper we use multi-temporal digital elevation ling studies have shown that these large ice caps could models (DEMs; Fig. 2), obtained by both satellite and lose most of their mass within 200Á300 years (e.g., airborne remote sensors, to estimate changes in the Adalgeirsdo´ ttir et al. 2005; Adalgeirsdo´ ttir et al. 2006) volume and the specific mass balance of the Eyjafjallajo¨ - and the most recent model runs, using a revised climate kull, Torfajo¨ kull and Tindfjallajo¨ kull ice caps over two change scenario, predict that these ice caps will disappear periods, from 1979Á1984 to 1998 and from 1998 to 2004, even faster, within 150Á200 years (Gudmundsson et al. investigating a phase of climate-driven glacier changes 2009). prior to the 2010 subglacial eruption in the Eyjafjallajo¨ - Observations of mass balance and volume change kull volcano. No traditional mass balance observations commonly serve as key inputs in studies of glacier are available from these small ice caps that are located in response to present-day climate variations as well as to and close to the most maritime climate in Iceland. The ice calibrate models used to predict the future outlook of dynamics have not been studied but our reconnaissance glaciers. Annual mass balance observations at locations of flights over the last decades have not revealed any surges. stakes have been conducted on the three largest ice caps The three ice caps under consideration are all located in Iceland. Such observation methods are time consum- on active volcanoes. The most hazardous of those is the ing, expensive and infeasible for inaccessible or steep and central volcano underneath the Eyjafjallajo¨ kull ice cap crevassed mountain glaciers. For a more comprehensive that started erupting in April 2010 (Gudmundsson et al. view of glacier changes in Iceland, we aim at obtaining 2010). It is evident from field surveys, reconnaissance volume and mass balance changes by remote-sensing flights as well as aerial and satellite photographs that the methods, i.e., by comparing recent elevation maps glacier surfaces of Eyjafjallajo¨ kull and Tindfjallajo¨ kull produced from remote-sensing data to older available showed no evidence of active subglacial geothermal areas maps (e.g., Berthier et al. 2004; Magnu´ sson et al. 2005a). over the time period from the 1980s to 2004 and only 2 Citation: Polar Research 2011, 30, 7282, DOI: 10.3402/polar.v30i0.7282 (page number not for citation purpose) S. Gudmundsson et al. Mass balance of three ice caps in southern Iceland Fig. 2 Shaded relief images of the Eyjafjallajo¨ kull (E), Tindfjallajo¨ kull (Ti), Torfajo¨ kull (To) and My´rdalsjo¨ kull ice caps and surrounding glacier free areas, based on digital elevation maps derived from: (a) SPOT 5 high-resolution stereoscopic images from 5 October 2004; (b) SPOT 5 HRS from 14 August; (c) Electromagnetic Institute Synthetic Aperture Radar Sensor (EMISAR) images from 12 August 1998; and (d) aerial photographs from 1979 (Torfajo¨ kull), 1980 (Tindfjallajo¨ kull) and 1984 (Eyjafjallajo¨ kull). Gaps in (a) and (b) allocate uncorrelated parts of the SPOT 5 HRS image pairs. Red indicates (a) airborne radar altimetry observed seasonally from 2004 to 2007, (b) the line of seasonal Ice, Cloud, and Land Elevation Satellite (ICESat) laser elevation data used in this study, observed from 2004 to 2007 and (c) global positioning system (GPS) profiles and sparse GPS observations at ice-free areas. Blue in (aÁd) indicates the ice cap margins. small, localized geothermal areas have been identified photographs taken between 1979 and 1984 in south beneath Torfajo¨ kull. Hence, the influence of subglacial Iceland, airborne Synthetic Aperture Radar (SAR) images geothermal heat on the total mass balance from the obtained on 12 August 1998 by the Electromagnetic 1980s to 2004 is small and can be neglected. Knowledge Institute (EMI), Technical University of Denmark and of ice volume changes is important for estimating high-resolution stereoscopic (HRS) images taken by the pressure release on underlying volcanoes as well as to SPOT 5 satellite on 14 August and 5 October 2004 quantify the amount of ice available for hazardous floods (Fig. 2; e.g., Korona et al. 2009). Elevations of the ice during a subglacial eruption. Observations of ice volume caps and surrounding ice-free areas were used to con- changes are needed when interpreting long-term con- strain, correct and evaluate the elevation maps. The global tinuous tilting, global positioning system (GPS) levelling positioning system (GPS) profiles on roads (Fig.
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