Francisca Bown

Recent glacier variations at the Aconcagua basin, central Chilean Andes

Abstract The majority of glaciers in central Chile have receded in recent decades, from >50m to only a few meters per year, mainly in response to an increase in the 0˚C isotherm altitude. The Aconcagua river basin (33˚ S) is one of the major glaciated basins in central Chile, with 121 km2 of ice in 2003. An earlier inventory using 1955 aerial photographs yielded a total surface area of 151 km2, implying a reduction in glacier area of 20% (0.63km2 a–1) over the 48 years. Photographic stereo models, high-resolution satellite images (Landsat, ASTER) and SRTM data have been used to delineate glacier basins. A focus on Glaciar Juncal Norte, one of the largest glaciers in the basin, allows a more detailed analysis of changes. The glacier has exhibited a smaller reduction (14%) between 1955 and 2006, and the resulting elevation changes over this smaller period are not significant. The above reduction rates are lower than in other glaciers of central Chile and Argentina. This trend emphasizes water runoff availability in a river where most of the water in the dry summers is generated by glaciers and snowpack, and where most of the superficial water rights are already allocated. Ongoing hydrological research including modelling of future water runoff will improve our understanding.

The surface energy balance of an active ice-covered volcano: Villarrica Volcano, Southern Chile

Abstract The energy balance of bare snow and tephra-covered ice near the glacier equilibrium line elevation on Villarrica Volcano, southern Chile, was investigated during 2004 and 2005, combining meteorological, surface temperature and ablation measurements with energy balance modelling. A tephra thermal conductivity of 0.35 Wm–1 K–1, and a critical tephra thickness of <5mm at which ablation is reduced compared to bare snow, were obtained from field data. These low values are attributable to the highly porous lapilli particles which make up most of the surface material. Modelled melt totals in the January to March period were 4.95 m and 3.96 m water equivalent (w.e.) in 2004 and 2005, respectively, compared with ∽0.5mw.e. melt for ice buried by >0.1m tephra. Windblown tephra impurities lowered snow albedo, but increased snowmelt by only an estimated 0.28mw.e. over the same period. The net mass balance impact of supraglacial tephra at Villarrica Volcano is therefore positive, as thick ash and lapilli mantle most of the glacier ablation zones, probably reducing annual ablation by several metres w.e. In the accumulation seasons, frequent melting events were recorded with modelled daily snowmelt rates of up to 50 mmw.e.

Glacier inventory of the upper Huasco valley, Norte Chico, Chile: glacier characteristics, glacier change and comparison with central Chile

Abstract Results of a new glacier inventory of the upper Huasco valley, which lies within the arid Norte Chico zone of the Chilean Andes, are presented for 2004. Despite the high altitude, the glaciation in this region is limited in extent and is not classical mountain glaciation, which poses difficulties in completing standard inventory attribute tables. Small cornice-style ridgeline features constitute a large number of the non-transient ice bodies identified, and glaciers with surface areas <0.1 km2 comprise 18% of the glacierized area and 3% of the water resource stored as glacier ice within the Huasco valley. Rock glaciers are an important component of the cryosphere, comprising 12% of the total water volume stored in glacial features. Changes in glacier area over the last ~50 years are in line with those for glaciers in central Chile despite the contrasting climate conditions. Projections of glacier area change based on glacier hypsometry and zero isotherm shifts predicted using the PRECIS regional model temperature change for IPCC scenario B2 conditions suggest that the survival of 65% of glacier area and 77% of active rock-glacier area will be threatened under forecast conditions for the end of the 21st century.

Ice volumetric changes on active volcanoes in southern Chile

Abstract Most of the glaciers in southern Chile have been retreating and shrinking during recent decades in response to atmospheric warming and decrease in precipitation. However, some glacier fluctuations are directly associated with the effusive and geothermal activity of ice-covered active volcanoes widely distributed in the region. The aim of this paper is to study the ice volumetric changes by comparing several topographic datasets. A maximum mean ice thinning rate of 0.81 ± 0.45 m a−1 was observed on the ash/debris-covered ablation area of Volcan Villarrica between 1961 and 2004, whilst on Volcan Mocho the signal-to-noise ratio was too small to yield any conclusion. An area reduction of 0.036 ±0.019 km2 a−1 since 1976 was obtained on Glaciar Mocho, while on Volcan Villarrica the area change was −0.090 ± 0.034 km2 a−1 between 1976 and 2005. Glaciers on active volcanoes are therefore shrinking, mainly in response to climatic driving factors. However, volcanic activity is affecting glaciers in two opposite ways: ash/debris advection is helping to reduce surface ablation at lower reaches by insulating the ice from solar radiation, while geothermal activity is probably enhancing melting and water production at the bedrock, resulting in negative ice-elevation changes.

Glacier responses to recent volcanic activity in Southern Chile

Glaciers in Southern Chile (39–43°S) are characterized by frontal retreats and area losses in response to the ongoing climatic changes at a timescale of decades. Superimposed on these longer-term trends, volcanic activity is thought to impact glaciers in variable ways. Debris–ash covered Glaciar Pichillancahue-Turbio only retreated slightly in recent decades in spite of been located on Volcan Villarrica which has experienced increased volcanic activity since 1977. In contrast, the negative long-term Volcan Michinmahuida glacier area trend reversed shortly before the beginning of the explosive eruption of nearby Volcan Chaiten in May 2008, when Glaciar Amarillo advanced and a lahar type of mudflow was observed. This advancing process is analysed in connection to the nearby eruption, producing albedo changes at Michinmahuida glaciers, as well as a possible enhanced basal melting from higher geothermal flux. Deconvolution of glacier responses due to these processes is difficult and probably not possible with available data. Much more work and data are required to determine the causes of present glacier behaviour.

Recent ice-surface-elevation changes of Fleming Glacier in response to the removal of the Wordie Ice Shelf, Antarctic Peninsula

Abstract Regional climate warming has caused several ice shelves on the Antarctic Peninsula to retreat and ultimately collapse during recent decades. Glaciers flowing into these retreating ice shelves have responded with accelerating ice flow and thinning. The Wordie Ice Shelf on the west coast of the Antarctic Peninsula was reported to have undergone a major areal reduction before 1989. Since then, this ice shelf has continued to retreat and now very little floating ice remains. Little information is currently available regarding the dynamic response of the glaciers feeding the Wordie Ice Shelf, but we describe a Chilean International Polar Year project, initiated in 2007, targeted at studying the glacier dynamics in this area and their relationship to local meteorological conditions. Various data were collected during field campaigns to Fleming Glacier in the austral summers of 2007/08 and 2008/09. In situ measurements of ice-flow velocity first made in 1974 were repeated and these confirm satellite-based assessments that velocity on the glacier has increased by 40–50% since 1974. Airborne lidar data collected in December 2008 can be compared with similar data collected in 2004 in collaboration with NASA and the Chilean Navy. This comparison indicates continued thinning of the glacier, with increasing rates of thinning downstream, with a mean of 4.1 ± 0.2 m a−1 at the grounding line of the glacier. These comparisons give little indication that the glacier is achieving a new equilibrium.

Glacier shrinkage and negative mass balance in the Chilean Lake District (40°S) / Rétrécissement glaciaire et bilan massique négatif dans la Région des Lacs du Chili (40°S)

Abstract Ice-capped volcanoes of the Chilean Lake District have shown significant glacier retreat during recent decades, probably in response to tropospheric warming and precipitation decrease. Volcán Mocho-Choshuenco (39°55′S, 72°02′W) is one of the main active volcanoes in this part of the country. A mass balance programme was initiated on its southeastern glacier in 2003, in view of its representative conditions as an ice body that is presumably not affected by current volcanic activity. The glaciers of this volcano have been retreating and shrinking in recent decades; by 2003 there had been a reduction of 40% of the original area of 28.4 km2 in 1976. A maximum decrease of area was observed in the most recently analysed period, a rate of 0.45 km2 year-1 between 1987 and 2003. The glacier average net mass balance of 2003/04 yielded −0.88 m w.e. (water equivalent) per year (±0.18), with an average net accumulation and ablation of 2.59 and −3.47 m w.e. per year, respectively. This is the first direct measurement of glacier mass balance in southern Chile, where very little is known about glacier variations and glacier–volcano interactions.

First Glacier Inventory and Recent Glacier Variation on Isla Grande de Tierra Del Fuego and Adjacent Islands in Southern Chile

The first glacier inventory of the islands south of the Estrecho de Magallanes including Isla Grande de Tierra del Fuego, Isla Santa Ines, and Isla Hoste, has been compiled using several ASTER and Landsat ETM+ satellite images acquired between 2001 and 2011, yielding a total glacier cover of 3,289.5 km2, distributed among 1,681 glaciers. Previous estimations of total glaciated area for these islands amounted to only 2,500 km2, the difference being attributed to more precise glacier delimitation—not to glacier advance. Most glacier tongues analyzed from recent remotely sensed imagery have been compared with historical data, with a number of glaciers showing retreat in recent decades, especially on the northern side of Cordillera Darwin and at Monte Sarmiento, both located on Isla Grande de Tierra del Fuego. Within the survey area of interest, Glaciar Marinelli showed the greatest change, with a frontal retreat of 15 km between 1913 and 2011. Many other glacier fronts have been stable, with only minor changes since the first historical accounts. Only two glaciers, located at the southern edge of Cordillera Darwin, have shown advances in the last decade; namely, Glaciar Garibaldi (+1.1 km between 2001 and 2007) and an unnamed glacier calving into Bahia Pia (+0.6 km between 1991 and 2004). These advancing glaciers seem to be responding to calving oscillations and not necessarily to the current climatic trend in the region of atmospheric warming and less precipitation.

Recent glacier changes in southern Chile and in the Antartic Peninsula

Se presenta una sintesis de la investigacion glaciologica reciente realizada por el Centro de Estudios Cientificos, CECS, en Chile y la Peninsula Antartica mediante el uso de una variedad de metodologias modernas, con el fin de detectar las tendencias de cambio experimentadas por los glaciares en las ultimas decadas.

The Patagonian ice fields: An updated assessment of sea level contribution

Climate Change: Global Risks, Challenges and Decisions IOP Conf. Series: Earth and Environmental Science 6 (2009) 012006 IOP Publishing doi:10.1088/1755-1307/6/1/012006 S01.06 The Patagonian ice fields: an updated assessment of sea level contribution Gino Casassa(1), W Krabill(2), A Rivera(0), J Wendt(1), A Wendt(1), P Lopez(1), F Bown(1), E Rignot(0), R Thomas(0), J Yungel(6), J Sonntag(6), E Frederick(6), R Russell(6), M Linkswiler(6), A Arendt(7), K Steffen(8) (1) CECS, Valdivia, Chile (2) Code 972, NASA-GSFC/WFF, Wallops Island, Virginia, USA (3) University of Chile, Santiago, Chile (4) School of Physical Sciences, University of California, Irvine, California, USA (5) JPL, Pasadena, California, USA (6) EG&G, NASA-GSFC/WFF, Wallops Island, Virginia, USA (7) Geophysical Institute, University of Alaska, Fairbanks, Alaska, U (8) CIRES, University of Colorado, Boulder, Colorado, USA The Northern and Southern Patagonia icefields (NPI and SPI) of southern South America have a total area of approximately 17,000 km 2 , constituting the largest temperate glacier system in the southern hemisphere. Snow precipitation can exceed 10 m/y water equivalent (w.e.) due to westerly air flow, with an important east-west gradient. In the lower reaches ablation can be larger than 10 m/y w.e., with abundant calving on fjords and freshwater lakes. The vast majority of the outlet glaciers show strong retreat and thinning in the ablation areas over the past century (Rignot et al., 2003), which can be largely explained by regional atmospheric warming. However, until now the data of the accumulation areas are insufficient for deriving the mass balance in the upper plateau. Here we compare new laser altimetry data of October 2008 with earlier data of November/December 2002 collected by airborne missions performed by NASA/CECS/Armada de Chile. The laser data are supplemented by the 2000 Shuttle Radar Topography Mission (SRTM) information and by 1975 and 1995 cartographic data of Chile. The data will allow to determine if thickening is occurring in the accumulation areas, as reported for example by Moeller et al. (2007) for Gran Campo Nevado, Patagonia, and if the rate of thinning at low elevations has experienced recent increases. As a result the contribution of the Patagonian icefields to sea level rise will be reassessed. c 2009 IOP Publishing Ltd