journal of Claciology (2016), 62(232) 391 ^01 doi: 10.101 7/jog.2016.43 ©The Author(s) 2016. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons. org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. Glacier area changes in the central Chilean and Argentinean Andes 1955-2013/14 JEPPE K. MALMROS,1 SEBASTIAN H. MERNILD,2'3 RYAN WILSON,4 JACOB C. YDE,2 RASMUS FENSHOLT1 1 Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark 2Faculty of Engineering and Science, Sogn og Fjordane University College, Sogndal, Norway 3Direction for Antarctic and Subantarctic Programs, Universidad de Magallanes, Punta Arenas, Chile 4Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, UK Correspondence: Jeppe Kjeldahl Malmros ABSTRACT. To improve our knowledge of glacier area changes in the central Chilean and Argentinean Andes (32°9'S-33°4'S), two new glacier inventories from 1989 to 2013/14 are compared with a reinterpreted inventory from 1955. Comparisons show glacier area retreat of 30 ± 3% since 1955, decreasing from 134 to 94 km2 in 2013/14, whilst the annual rate of area loss showed a small increase (insignificant) between the periods of 1955-1989 and 1989-2013/14. Separate analysis of the 1989 and 2013/14 inventories, including a larger sample, revealed a higher rate of glacier change compared with the smaller samples of these inventories. Additionally, an analysis at ~5 year intervals for six major glaciers (1955-2013) indicates large variability in response times and area loss magnitudes. Glacier Olivares Alfa, for example, lost 63% of its ice area, while the Juncal Norte Glacier lost only 10% (1955-2013). The findings from this study improve our current knowledge base concerning widespread glacier decline in the southern Andes, and furthers monitoring efforts in this poorly described region of the world, a region containing vital water resources for populated areas in South America. KEYWORDS: climate change, glacier delineation, glacier fluctuations, glacier mapping, remote sensing 1. INTRODUCTION In line with most regions of the world, glaciers in southern South America have retreated and thinned in response to climate changes since the end of the Little Ice Age (LIA) (Masiokas and others, 2006; Le Quesne and others, 2009; Mernild and others, 2015). For the relatively well-examined southern Patagonia region, studies have revealed post-LIA glacier area losses in the order of 11-14% (~1870-2011) (Davies and Glasser, 2012; Falaschi and others, 2013) and area change rates of —0.2% a-1 in recent years (2000/02-2008/10) (White and Copland, 2015). To the north, in the semi-arid central Chilean and Argentinean Andes, only relatively few studies have coupled glacier changes with climate dynamics (e.g., Lliboutry, 1998; Leiva, 1999; Pel I icciotti and others, 2007, 2008, 2014) showing that glaciers in this region are shrinking and losing mass. The glacier inventories available for the central Chilean and Argentinean Andes, compiled from a wide variety of sources (e.g. aerial photography, satellite imagery and historic maps), are currently relatively few in number, with most including only a small number of glaciers (e.g., Lliboutry, 1956; Marangunic, 1979; Valdivia, 1984; Garin, 1987; Aniya and others, 1996; Leiva, 1999; Nicholson and others, 2009; Rabatel and others, 2011). Although indicating glacier retreat, these inventories and glacier change studies cover different time intervals throughout the 20th and 21st centuries, making direct glacier comparisons difficult. Due to these limitations, detailed assessments of long-term glacier changes in the central Chilean and Argentinean Andes (besides length changes) are to a large extent still missing (Pellicciotti and others, 2014); a circumstance that is limiting our understanding of glacier/climate interactions in this region. Climate conditions in this part of the Chilean and Argentinean Andes (31-35°S) are semi-arid and Mediterranean in type (Lliboutry, 1998), with regional-scale weather conditions being largely controlled by the seasonal displacement of a high-pressure cell above the southeastern Pacific Ocean (Rutllant and Fuenzalida, 1991), which inhibits precipitation in summer and allows for the passage of westerlies and subsequent frontal precipitation during Austral winters (May-August) (Garreaud and others, 2009). Also, precipitation amounts two to three times greater than at sea level are present at west-facing Andes slopes due to the orographic uplift of low-level air, while dry leeward conditions prevail on eastern Andes slopes (Garreaud and others, 2009). Precipitation amounts between 30°S and 35°S are influenced by the El Nino Southern Oscillation (ENSO), with above average annual precipitation totals during El Nino events and below average totals during La Nina events (e.g. Rutllant and Fuenzalida, 1991; Escobar and others, 1995; Leiva, 1999; Montecinos and Aceituno, 2003; Garreaud and others, 2009; Gascoin and others, 2011; Mernild and others, 2015). ENSO events have also been linked to increases in winter snowfall and a higher frequency of avalanches in the central Chilean Andes (Masiokas and others, 2006; McClung, 2013). Evidence suggests that precipitation patterns in the central Chilean and Argentinean Andes have undergone significant changes over the past ~30 year (Pellicciotti and others, 2007). Higher frequencies of above average winter snow accumulation have been observed in the central Andes Cordillera since 1976 (Masiokas and others, 2009), with particularly large snow accumulation events occurring between 1980 and 1985 (Masiokas and others, 2006). From the mid-1970s to Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:34:50, subject to the Cambridge Core terms of use, available at https:/www.cambridge . https://doi.org/! 0.1017/jog.2016.43 392 Malmros and others: Clacier area changes in the central Chilean and Argentinean Andes 1955-2013/14 2001, for example, large precipitation events have become less frequent but more intense (Carrasco and others, 2005). These precipitation changes, together with observed reductions in seasonal snow cover, have resulted in reduced levels of runoff in the central Chilean Andes (Pellicciotti and others, 2007). In addition, an air temperature increase of ~0.25°C per decade, has been observed for the central Andes between 1975 and 2001 (Rosenbluth and others, 1997; Falvey and Garreaud, 2009), resulting in a rise of the 0°C isotherm by ~120 m in winter and ~200 m in summer (Carrasco and others, 2005). Central Chilean and Argentinean glaciers constitute important water resources for downstream populations (Mernild and others, 2015). Although river runoff in this region is mainly sourced from snowmelt (Favier and others, 2009), during the late ablation season when seasonal snow has melted, runoff from glacier melt increases in importance. Glacier meltwater is thus an important freshwater resource for urban and agricultural areas. In the Rio Maipo basin, the main river basin of Region Metropolitan a, water resources are reduced during dry summers especially when preceded by episodic winter droughts (Meza and others, 2012). During such events up to 67% of the river discharge in Rio Maipo originates from glacier ablation in the Chilean central Andes (Peha and Nazarala, 1987). Previous work has reported glacier changes at Juncal Sur, Olivares Beta, Olivares Gamma and Olivares Alfa in the Rio Olivares basin (Lliboutry, 1998; Masiokas and others, 2009; Gacitua and others, 2015), and glacier Juncal Norte in the Aconcagua basin (Pellicciotti and others, 2007, 2008; Bown and others, 2008). These studies provide information on area and length changes, thinning rates and thermal regime. Additional studies for larger glaciers in the upper part of the Rio del Plomo basin include information on length and hypsometry (Llorens and Leiva, 1995; Leiva, 1999). Overall, these studies have indicated that glaciers in the region are thinning and losing area as a consequence of changing climatic conditions (Pellicciotti and others, 2014). However, consistency in mapping methods and use of imagery for these studies were, to a large extent, lacking. For some of these studies, this sadly inhibits comparability and re-usability of data. In this study we aim to establish a foundation for future glacier monitoring studies by consistently quantifying glacier area change in one of the most glacierized areas of the central Chilean and Argentinean Andes (32°9'-33°4'S) over a 58/59 year period between 1955 and 2013/14. Our analysis is based on a comparison between a reinterpreted version of an existing glacier inventory from 1955, derived from aerial imagery using georeferenced original aerial imagery (Marangunic, 1979), and two new glacier inventories from 1989 and 2013/14. The two new glacier inventories used were compiled from co-registered Landsat 5, Landsat 8 and GeoEye-1 satellite imagery. In addition, we examine in detail, six of the largest glaciers, located in and around the Rio Olivares basin (in the center part of the study area), at ~5 year intervals between 1955 and 2013/14 in order to gain further insight into the temporal variability of glacier change in this region. 2. STUDY AREA The study area is located in the central Chilean and Argentinean Andes ~50 km northeast of Santiago de Chile (32°9'-33°4'S), and covers an area of 1958 km2 (Fig. 1). Mountain peaks in this area reach altitudes >6000 m, with the central massifs marking the dividing line between two distinctly different climate systems on the east and the west of the cordillera. As of 2013/14, ~8% of the study area was glacierized, including valley, mountain and cirque type glaciers varying in size from ~0.05 to ~21 km2. The study area also includes a number of fully debris-covered glaciers and rock glaciers that are excluded from sampling. The majority of the ~300 individual glaciers (as of 2013/14) are located in the northern part of the study area at elevations between ~2900 and ~6100m a.s.l. Here, glaciers are distributed at mean elevations between ~3300 and ~5500 m a.s.l., with the majority of the glacierized area located between ~4200 and -4500 m a.s.l. (Fig. 2). Glaciers in this study area supply runoff to several important river basins including the Rio Aconcagua (north), Rio Molino (west), Rio del Plomo (sub-catchment of the Rio Tupungato) (east), and two sub-catchments of the Rio Maipo, Rio Olivares and Rio Colorado (south) (Fig. 1b). A few specific glaciers in the study area are identified as surge-type glaciers. The glacier Grande del Nevado on the eastern slopes of the Nevado del Juncal massive, for Fig. 1. (a) The location of the study site in central Chile and Argentina highlighted with a black bold rectangle, (b) The location of Rio Olivares basin and neighboring basins: b-1 Rio Maipo, b-2 Rio Aconcagua and b-3 Rio del Plomo. (c) The glaciers in and around the Rio Olivares basin identified in 2013/14 and highlighted in light blue. Red dots indicate the six large glaciers selected for detailed temporal analysis (image: Landsat 8, 10 February, 2014). Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:34:50, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms . https://doi.org/! 0.1017/jog.2016.43 Malmros and others: Clacier area changes in the central Chilean and Argentinean Andes 1955-2013/14 393 example, surged in 1933 and again in 1984 (Espizua and Lydia, 1986). Suspected surging activity was also observed at the glacier Juncal Sur on the west side of the same massive between 1946 and 1947 (Lliboutry, 1998). 3. METHODS AND MATERIALS 3.1 Imagery Image sources include: (1) aerial photography from 1955 acquired by the Chilean military Instituto Geogräfico Militär (available from Direccion General de Aguas (DGA)), (2) declassified Optical Corona spy satellite images (1967), (3) Landsat 2 - Multispectral Scanner (MSS) (1975), (4) Landsat 5 - Thematic Mapper (TM) (1985-2010), (5) Landsat 7 -Enhanced Thematic Mapper Plus (ETM+) (2000-2003), (6) Landsat 8 - Operational Land Imager (OLI) (2014), (7) Advanced Spaceborne Thermal Emission and Radiometer (ASTER) (2008, 2010), and (8) ortho-projected GeoEye-1 satellite imagery (2013). All selected images were acquired during the late ablation season (February-April), when seasonal snow cover is at a minimum. The Corona and Landsat satellite imagery used was acquired from the USGS Earth Explorer (http://earthexplorer.usgs.gov/) and the Global Visualization Viewer (http://glovis.usgs.gov/) web-portals. The 2013 GeoEye-1 scenes were acquired from DigitalGlobe (http//:www.digitalglobe.com). Elevation data were obtained from the ASTER Global DEM (GDEM) v.2 (Tachikawa and others, 2011), with a mean vertical error of ±2.12 m over South America when compared with ICESat Geosciences Laser Altimeter System (GLAS) measurements. Images used for the glacier subsample analysis were temporally distributed with a maximum gap of 12 years (1955-1967). The individual observation years include: 1955, 1967, 1975, 1985, 1989, 1994, 2000, 2002, 2008, 2010 and 2013/14. For the glacier elevation changes estimated between each observation period, it should be noted that these are functions of 2-D planimetric area changes over a static raster DEM data (perimeter elevation). As the ASTER GDEM v.2 elevation data originate from best observation ASTER stereo image pairs acquired between 2000 and 2010, glacier elevations estimated prior to and after these observation years may include additional uncertainties brought about by temporal ice surface thickening and thinning. In this study these elevation changes should be seen as estimates, not ground truth measurements. 3.2 Misclassification errors and uncertainties Prior to glacier mapping, each of the image datasets were co-registered to the 2014 Landsat 8 scene (using 27-35 ground control points). The resulting RMSE values varied from ±2 m (1955 aerial imagery), ±8 m (ETM+) and ±38 m (MSS). The RMSE values are largely dependent on image pixel resolution, with the coarsest resolutions producing the highest errors. Source image pixel resolutions ranged from 4 m (GeoEye-1) to 60 m (MMS). Potential glacier outline delineation errors (misclassifica-tions) were calculated following the method by Williams and others (1997). The maximum possible glacier delineation errors for the 1955, 1989 and 2013/14 inventories were calculated as ~2, ~15 and ~4%, respectively. The average delineation error for the sub-selected glaciers in the Rio Olivares basin varied from 0.3% for the 1955 Glacierized area {km") IÜ 20 30 40 SO 60 550O-S60O 5400-5500 5300-5400 5200-5300 5 100-5200 5000-5 100 4900-5000 4800-4900 CI 4700-4800 20.0 Size interval (km1) Frequency Area % 1955 1955 I-1 1989 —*— 1989 2013/2014 —•— 2013/2014 Fig. 4. (a) Clacier size intervals in relation to number of glaciers (bars) and area cover percentage (lines), (b) Clacier distribution, in regard to aspect, for glaciers present in all inventories (1955, 1989 and 2013/14). Between 1989 and 2013/14 glacier area reduced by 27.4 km2 (-16%), from 171.7 km2 in 1989 to 144.3 km2 in 2013/ 14, with a mean area change rate of —1.1 km2 a-1 (—0.7% a-1) over the 24/25 a. The majority of the area loss for this period was identified for glaciers with mean elevations between 4000 and 4400 m a.s.l. (Fig. 2, bars). Not surprisingly, relative area changes for the glaciers in this study showed an inverse relationship with elevation. On average glaciers with mean elevations below 3600 m a.s.l. showed area loss of >30% between 1989 and 2013/14 and glaciers with mean elevations above 5200 m a.s.l. showed area losses of <10%. Throughout the observation period mean glacier size decreased by 37%, from 0.74 km2 in 1989 to 0.48 km2 in 2013/14, similar to that observed for the 1955 sample. The number and total area of glaciers per size interval is plotted on Fig. 4a, showing that glaciers in the <0.1 and 0.1-0.5 km2 intervals contain the highest number of glaciers, accounting for 79% (1989) and 88% (2013/14) of the combined glacier samples, respectively. Over the observation period, the number of individual glaciers in these two intervals increased from 1 83 to 265. However, the area contained within these intervals constitutes only 13 and 1 7% of the total glacierized area in 1989 and 2013/14, respectively 40 20 -20 -40 -60 -SO 100 0 □ 1955-1989 O 5989-2013 A 1955-2013 -A <>A AA ffi mi-g—r A a □ □ o o 0 00 n A C^5h-O oftPa A A A n O 00 D © A - A <> o "□H-1—r-r O O 0.1 1.0 Initial 1955arca(kmJ) 10.0 SO.O Fig. 5. Relative glacier area changes in % from 1955 to 1989, 1989-2013 and 1955-2013. (Fig. 4b). In contrast, the 1-5 km2 interval contained the largest glacier areas, including 26 and 2 7% in 1989 and 2013/14, respectively. In 2013/14, Juncal Sur (>20 km2) and Olivares Gamma (10-20 km2) were the only two glaciers left in these intervals. 4.3 Glacier subsample All the six subsample glaciers experienced area loss during the 58 a observation period, but at varying rates. Together, these six glaciers accounted for 63% or 25.2 km2 of the total area loss shown for the 1955-2013/14 sample (40.3 km2). As a result, these glaciers constitute the most important contributors to glacier area loss in the study area. To some extent, these individual glacier variations are comparable with previous glacier monitoring studies (Table 3). The largest glacier in the study area, Juncal Sur, showed the second largest absolute area loss of 5.3 km2, corresponding to 21 % of its 1955 area (Figs 6a, b; Table 4). In terms of relative area change, this is comparable with the Olivares Gamma and Esmeralda glaciers, which reduced by 21% (3 km2, 0.4% a-1) and 20% (1.4 km2, 0.3% a-1), respectively. Area changes for Olivares Beta Glacier showed a similar pattern as the above mentioned glaciers only after the initial 1955-1967 period, when substantial area reductions took place. Overall, the Olivares Beta Glacier lost 4.3 km2 or 34% (0.6% a-1) of its 1955 area during the 58 years. A second distinct pattern can be seen at the Juncal Norte Glacier, which reduced by only 11% (0.8 km2, 0.2% a-1) since 1955. Echaurren Norte, unlike the above, showed only minor area reduction before the 1990s, after which it mirrors the patterns of the other glaciers. A period of growth or stagnation between 2000 and 2008 was observed on all above mentioned glaciers. However, at the end of the time series 2008-2013 all these glaciers initiated a strong recession indicating a symmetry in response time. A third distinct pattern is observed for the Olivares Alfa Glacier. This glacier reduced by 63% (—10.5 km2, —1.1% a-1) in area between 1955 and 2013. This is in both relative and absolute Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:34:50, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms . https://doi.org/! 0.1017/jog.2016.43 Malmros and others: Clacier area changes in the central Chilean and Argentinean Andes 1955-2013/14 397 Table 3. Comparison between the glac er change results presented in this study and in previous studies Glacier 1955 Area Study Area Area Area Length Length Source period change change change rate change change rate km2 Year km2 % % a"1 M m a-' Juncal 25.6 1955-1997 -2.8 -10.9 -0.3 -2108 -50 Rivera and others (2002) Sur 25.8 1955-1994 -3.7 -14.3 -0.4 -2734 -70 This study Olivares 14.7 1955-1997 -0.4 Rivera and others (2000) Gamma 1955-1997 -1.2 -8.2 -0.2 -623 -15 Rivera and others (2002) 14.4 1955-1994 -2.3 -16.2 -0.4 -979 -25 This study Olivares 1955-1979 -1000 -42 Lliboutry (1998) Beta 1955-1997 -898 -21 Rivera and others (2002) 1955-1994 -1.2 Rivera and others (2000) 12.5 1955-1975 -575 -29 This study 1955-1994 -3.7 -29.8 -0.8 -753 -19 This study Juncal 9.0 1955-1997 -0.2 2.4 -0.1 -170 -4 Rivera and others (2002) Norte 1997-2000 -12 -4 Rivera and others (2002) 1955-1997 -0.1 -0.9 0.0 -120 -4 Bown and others (2008) 1989-1997 -1.0 -11.1 -1.4 -185 -23 Bown and others (2008) 1997-1999 0.0 -0.3 -0.2 -40 -20 Bown and others (2008) 1999-2006 -0.4 -3.9 -0.6 -119 -17 Bown and others (2008) 1955-2006 -1.5 -16.2 -0.3 -464 -9 Bown and others (2008) 7.5 1955-1994 -0.3 -3.5 -0.1 -212 -5 This study 1994-2000 -0.3 -4.1 -0.7 -197 -33 This study 2000-2008 -0.2 -2.1 -0.3 -260 -33 This study 1955-2008 -0.4 -5.6 -0.1 -472 -9 This study l*SS 196$ 1*75 l**S HAS 2015 Fig. 6. Area and length change for the glacier subsample between 1955 and 2013/2014: (a) Glacier area changes (km2), (b) Relative glacier area changes (%). (c) Glacier length changes, (d) Glacier length fluctuations (m a~1). (e) Front elevation variations (m). Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:34:50, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms . https://doi.Org/10.1017/jog.2016.43 398 Malmros and others: Clacier area changes in the central Chilean and Argentinean Andes 1955-2013/14 Table 4. Observed area (including uncertainty), elevation and length from 1955 to 2013 for the subsample glaciers. Relative area and length changes (%) for each glacier are also shown Date Area Area Elevation Slope A Length Area Area Area Area a± Min Max mean Mean length A a"1 A A a"1 2(A) 2(A) % Juncal -70.12°E ; 33.10°S Sur km2 m a.s.l deg m m a-' km2 % 24 February 1955 25.8 0.3 2608 5860 3809 15.8 - - - - - - 5 March 1967 24.6 0.3 3555 5695 4333 16.0 -887 -73.8 -1.19 -0.10 -1.19 4.6 14 February 1975 24.0 4.2 3589 5718 4363 16.2 -403 -50.7 -0.65 -0.08 -1.84 7.1 14 March 1985 23.2 1.8 3595 5695 4364 16.1 -446 -44.3 -0.80 -0.08 -2.64 10.2 2 March 1989 22.5 2.0 3665 5695 4364 16.1 -305 -76.9 -0.65 -0.16 -3.29 12.8 27 February 1994 22.1 1.9 3675 5713 4373 16.2 -693 -138.8 -0.39 -0.08 -3.68 14.3 31 March 2000 21.5 0.9 3775 5695 4380 16.0 -610 -100.2 -0.67 -0.11 -4.35 16.9 21 March 2002 21.3 0.9 3772 5695 4382 16.4 -81 -41.1 -0.13 -0.07 -4.48 17.4 30 March 2008 21.6 0.9 3782 5695 4386 16.8 -136 -22.6 0.24 0.04 -4.24 16.4 30 January 2010 21.2 1.0 3782 5713 4385 16.4 0 0.0 -0.41 -0.22 -4.65 18.0 27 March 2013 20.5 1.0 3791 5718 4385 16.8 -223 -70.7 -0.65 -0.21 -5.30 20.5 Total -5.3 1183 -142 576 1.0 -3784 -5.30 -5.30 -20.5 Mean 1.4 -61.9 -0.11 - Olivares -70.22°E , 33.19°S Alfa km2 m a.s.l deg m m a-' km2 % 24 February 1955 16.6 0.2 3750 5120 4438 15.0 - - - - - - 5 March 1967 14.6 0.2 3906 4987 4357 15.7 -250 -20.8 -2.04 -0.17 -2.04 12.3 14 February 1975 14.2 3.3 3947 4996 4386 15.8 -150 -18.9 -0.41 -0.05 -2.45 14.7 14 March 1985 12.6 1.5 3942 4943 4392 15.5 -125 -12.4 -1.64 -0.16 -4.09 24.6 2 March 1989 11.0 1.6 3999 4943 4410 15.3 -76 -19.2 -1.56 -0.39 -5.65 34.0 27 February 1994 10.0 1.7 4010 4933 4440 15.5 -706 -141.4 -1.03 -0.21 -6.68 40.1 31 March 2000 8.5 0.8 4013 4933 4464 15.0 -165 -27.1 -1.49 -0.24 -8.17 49.1 21 March 2002 8.4 0.8 4019 4943 4477 15.4 -93 -47.2 -0.11 -0.06 -8.28 49.8 30 March 2008 7.6 0.7 4030 4933 4492 15.9 -387 -64.2 -0.74 -0.12 -9.02 54.2 30 January 2010 7.0 0.7 4043 4943 4505 15.1 -76 -41.4 -0.58 -0.32 -9.60 57.7 27 March 2013 6.2 0.7 4048 4933 4514 15.9 -25 -7.9 -0.87 -0.28 -10.47 62.9 Total -10.5 298 -187 76 0.9 -2053 -10.47 -10.47 -62.9 Mean 1.1 -40.0 -0.20 - Olivares -70.1 7°E , 33.12°S Gamma km2 m a.s.l deg m m a-' km2 % 24 February 1955 14.4 0.1 3492 4981 4328 15.8 - - - - - - 5 March 1967 13.8 0.2 3585 4966 4350 15.9 -403 -33.5 -0.57 -0.05 -0.57 4.0 14 February 1975 12.9 2.2 3587 4981 4380 15.9 -249 -31.3 -0.95 -0.12 -1.52 10.6 14 March 1985 13.0 1.0 3587 4981 4380 15.9 -138 -13.7 0.18 0.02 -1.34 9.3 2 March 1989 12.2 1.0 3587 4981 4390 15.8 -74 -18.7 -0.82 -0.21 -2.16 15.0 27 February 1994 12.1 1.0 3596 4953 4395 15.9 -115 -23.0 -0.17 -0.03 -2.33 16.2 31 March 2000 11.7 0.5 3609 4950 4401 15.8 -115 -18.9 -0.37 -0.06 -2.70 18.8 21 March 2002 11.7 0.5 3613 4963 4403 16.6 -50 -25.4 0.05 0.03 -2.65 18.4 30 March 2008 11.9 0.5 3613 4981 4404 16.1 -70 -11.6 0.14 0.02 -2.51 17.5 30 January 2010 11.8 0.5 3620 4966 4410 16.5 0 0.0 -0.11 -0.06 -2.62 18.2 27 March 2013 11.4 0.5 3627 4981 4411 16.3 -50 -15.9 -0.33 -0.10 -2.95 20.5 Total -2.3 135 0 83 0.5 -1264 -2.95 -2.95 -20.5 Mean 0.7 -19.2 -0.06 - Olivares -70.20°E , 33.14°S Beta km2 m a.s.l deg m m a-' km2 % 24 February 1955 12.5 0.2 3376 4900 4143 14.0 - - - - - - 5 March 1967 9.9 0.1 3669 4899 4466 13.9 -275 -22.9 -2.64 -0.22 -2.64 21.1 14 February 1975 9.7 2.0 3675 4899 4486 13.9 -300 -37.7 -0.20 -0.03 -2.84 22.7 14 March 1985 9.1 0.8 3712 4899 4490 14.0 -283 -28.1 -0.55 -0.05 -3.39 27.1 2 March 1989 8.8 0.8 3705 4899 4488 14.0 71 17.9 -0.31 -0.08 -3.70 29.6 27 February 1994 8.8 0.8 3705 4899 4487 14.1 34 6.8 -0.03 -0.01 -3.73 29.8 31 March 2000 8.5 0.4 3710 4899 4492 14.1 -30 -4.9 -0.31 -0.05 -4.04 32.3 21 March 2002 8.7 0.4 3780 4899 4490 14.0 -40 -20.3 0.20 0.10 -3.84 30.7 30 March 2008 8.6 0.4 3815 4899 4491 14.2 -40 -6.6 -0.04 -0.01 -3.88 31.0 30 January 2010 8.6 0.4 3772 4899 4493 14.2 -25 -13.6 -0.05 -0.03 -3.93 31.4 27 March 2013 8.2 0.1 3719 4899 4493 15.6 -47 -14.9 -0.36 -0.11 -4.29 34.3 Total -4.3 343 -1 350 1.6 -935 -4.29 -4.29 -34.3 Mean 0.6 -12.4 -0.05 - Juncal -70.10°E , 33.03°S Norte km2 m a.s.l deg m m a-' km2 % 24 February 1955 7.5 0.1 2878 5866 4611 26.6 - - - - - - 5 March 1967 7.5 0.1 2904 5866 4633 26.7 -272 -22.6 0.00 0.00 0.00 0.0 Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:34:50, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms . https://doi.Org/10.1017/jog.2016.43 Malmros and others: Clacier area changes in the central Chilean and Argentinean Andes 1955-2013/14 399 Table 4. (Cont.) Date Area Area Elevation Slope A Length Area Area Area Area a± Min Max mean Mean length A a"1 A A a"1 2(A) 2(A) % 14 February 1975 7.4 1.8 2916 5866 4638 26.6 -275 -34.6 0.12 0.02 0.12 1.6 14 March 1985 7.4 0.8 2901 5866 4618 26.6 232 23.0 0.00 0.00 0.12 1.6 2 March 1 989 7.4 0.8 2903 5866 4608 26.5 140 35.3 0.02 0.01 0.14 1.9 27 February 1994 7.3 0.8 2903 5866 4626 26.6 -37 -7.4 0.12 0.02 0.26 3.5 31 Mar 2000 7.0 0.4 2904 5866 4648 26.5 -160 -26.3 0.29 0.05 0.55 7.3 21 March 2002 7.0 0.4 2906 5866 4647 26.7 -50 -25.4 -0.04 -0.02 0.51 6.8 30 March 2008 7.1 0.4 2908 5866 4630 26.9 -50 -8.3 -0.09 -0.01 0.42 5.6 30 January 2010 6.9 0.4 2941 5866 4661 27.0 0 0.0 0.24 0.13 0.66 8.8 27 March 2013 6.7 0.1 2934 5866 4672 26.9 20 6.3 0.13 0.04 0.79 10.5 Total -0.8 56 0 61 0.3 -452 0.79 0.79 -10.5 Mean 0.5 -6.0 0.02 - Esmeralda -70.20°E, 33.22°S km2 m a.s.l deg m m a-' km2 % 24 February 1955 6.7 0.1 3490 5545 4850 20.6 - - - - - - 5 March 1967 6.4 0.1 3312 5361 4851 20.9 -160 -13.3 0.38 0.03 0.38 5.6 14 March 1985 6.3 0.8 3351 5366 4859 21.0 -200 -11.1 0.05 0.00 0.43 6.4 2 March 1 989 5.9 0.7 3321 5363 4866 21.1 100 25.2 0.36 0.09 0.79 11.7 27 February 1994 5.8 0.7 3335 5356 4883 21.2 -50 -10.0 0.12 0.02 0.91 13.5 31 March 2000 5.8 0.4 3365 5364 4886 21.3 -95 -15.6 0.02 0.00 0.93 13.8 21 March 2002 5.7 0.4 3449 5363 4890 22.9 -65 -33.0 0.08 0.04 1.01 15.0 30 January 2010 5.7 0.4 3544 5356 4898 21.7 -97 -12.3 0.02 0.00 1.03 15.3 27 March 2013 5.4 0.1 3568 5364 4904 21.3 -52 -16.5 0.32 0.10 1.35 20.1 Total 5.4 3568 5364 54 21.3 -619 1.35 1.35 -20.1 Mean 0.4 -10.8 0.04 - area reduction, considerably larger than for the similarly sized glaciers described above and around twice that for the mean inventory glacier for the same period as seen in Fig. 6b. While Olivares Alfa shows continuous area loss throughout the period, between 1967 and 1975, and again between 2000 and 2008, the rate of reduction slowed down. This later period in turn coincides with the period of glacier growth for the five glaciers, showing a common pattern in response to changing climate conditions. Variability in glacier length is often viewed upon as a natural indicator of past climate change and has, for example, been used to assess the effect of glacier changes on mountain hydrology (e.g. Shiyin and others, 2003; Leclercq and others, 2014). The pattern of glacier length changes for the six subsample glaciers, in many ways, resembles the pattern found in area changes. This is mainly due to the fact that glacier ablation under normal conditions is dominant at the lower elevation parts of a glacier, below the equilibrium line and especially near the front. When considering frontal changes for the subsample, Juncal Sur Glacier stands out (Fig. 6c). This glacier retreated by 3784 m, the largest retreat of all the six glaciers, averaging —62 ma-1. Two periods of especially rapid rate of frontal retreat for Juncal Sur were observed for 1955-1967 and 1989-2000, the later period with >100 m a-1 (Fig. 6d). An interesting observation is that the only other glacier showing similar behavior is Olivares Alfa. Overall, glacier front positions for Olivares Alfa retreated 2053 m (-40 ma-1) between 1955 and 2013. The frontal retreat of Olivares Alfa peaked between 1989 and 2000, with a rate of 141 m a-1, exceeding that observed for Juncal Sur between 2002 and 2010. A second pattern is identified for the Esmeralda, Olivares Beta and Juncal Norte glaciers, which retreated by 619 m (—11 m a-1), 935 m (-12maH) and 452 m (-6ma1, respectively. These three glaciers experienced periodic events of front advance between 1975 and 1989 and, for Juncal Norte, again between 2002 and 2010. A third pattern is found for Olivares Gamma, where the front retreated by 1264 m (—19 m a-1). Olivares Gamma, unlike the others, had a relatively stable front, showing continuous retreat without many fluctuations. The retreat experienced by these six glaciers changed the elevation of the fronts but at very different rates. The front elevation for Juncal Sur increased by 1183 m, and in 1955 the glacier was still retreating from its 1947 surge maximum. Front elevations for Olivares Alfa, Beta and Gamma glaciers changed more moderately by 298, 135 and 343 m, respectively, while the fronts of Juncal Norte and Esmeralda changed by 56 and 78 m, respectively (Fig. 6e). Higher frequencies of above average winter snow accumulation, observed since 1976 at the Echaurren Norte Glacier, ~200 km south of the subsample glaciers, and high snow accumulation events from 1980 to 1985 (Masiokas and others, 2006), could have played a role in the evolution of these glaciers. During the period 1975-1989 some of the glaciers stabilized and Olivares Gamma showed a small area gain, while Juncal Sur and Olivares Beta and especially Alfa, showed substantial area loss. There are several possible causes that may explain Olivares Alfa's particularly dramatic ice area loss. One hypothesis is that Olivares Alfa is more sensitive to recent climate change compared with other glaciers in the area because it is polythermal in type (Gacitua and others, 2015). Alternatively, the increased climate sensitivity could be related to its location on eastern-facing leeward slopes, which may receive less precipitation. Another factor that may influence the climate sensitivity of both Olivares Alfa and Olivares Beta is the proximity to the Los Bronces open Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:34:50, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms . https://doi.org/! 0.1017/jog.2016.43 400 Malmros and others: Clacier area changes in the central Chilean and Argentinean Andes 1955-2013/14 pit mine (opened in 1970). Deposition of mining related dust particles on the surface of these two glaciers could influence surface energy balances as shown, for example, on glaciers in the Alps (Oerlemans and others, 2009). 5. CONCLUSION AND FUTURE PERSPECTIVES We compiled two new inventories from 1989 and 2013/14 and performed a reinterpretation of an existing inventory from 1955 covering an important glacierized area of the central Chilean and Argentinean Andes. Inventory comparisons revealed widespread glacier shrinkages of 30 ±3% (0.5% a-1) from 1955 to 2013/14. Due to the disintegration of medium and large sized glaciers, caused by thinning and frontal retreat, mean glacier size decreased by 64%, while individual glacier numbers increased from 70 to 136 during the 58/59 year study period. Comparisons between the 1955, 1989 and 2013/14 inventories also revealed a small but insignificant increase in relative area loss rates. This comparison indicated a relatively constant trend in overall glacier area loss since 1955. During the study period, glacier minimum elevation increased by 108 m between 1955 and 1989, and a further 138 m from 1989 to 2013/14. The detailed analysis of six major glaciers located in and around the Rio Olivares basin revealed varying rates and magnitudes of area change and frontal retreat. The Olivares Alfa Glacier particularly stood out during this analysis, having reduced in area by 63% since 1955. Ongoing studies concerning mass balance and water resource potential have been initiated by the DGA on several glaciers in the area, including Olivares Alfa and Beta glaciers. A separate mass balance study is also ongoing on Olivares Gamma. We hope these studies in time will improve our understanding of glaciers in this region. Also, recent development in multispectral high-resolution image availability is expected to be of particular importance for the central Andes of Chile and Argentina, where many glacierized areas have not yet been sufficiently mapped. ACKNOWLEDGEMENTS This study was funded by the National Science Foundation of Chile FONDECYT under Grant Agreement #1140172, and by Centra de Estudios Cientfficos (CECs), which is funded by the Chilean Government through the Centers of Excellence Base Financing Program of CONICYT. 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