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.
A synthesis of glaciological studies carried out in Chile during recent decades is presented, including inventories and records of glacier variations, fluctuations of which are related to regional climate change and their contribution to eustatic sea-level rise. Based upon satellite imagery, aerial photographs and historical records, new data for 20 glaciers are presented. These new data are combined with previous records to cover the historical variations of 95 Chilean glaciers. Of these glaciers, only 6% show a net advance during the study period, 6% show no significant change, while 88% have retreated. The contribution of Chilean glaciers to eustatic sea-level rise has been estimated to be approximately 8.2% of the worldwide contribution of small glaciers on Earth during the last 51 years. Most of the glacier variations are thought to have been driven by a temperature increase, which has been documented by several stations in Chile. Anomalies in rainfall, and the decreasing trend in annual precipitation shown at a few stations, have probably also contributed to glacier recession. Based on observed climatic trends, it is expected that the glacier retreat will continue, that the mass balance will continue to show a negative trend and that thinning rates will increase. All of these changes will ultimately affect the availability of water resources in Chile that depend on glacierized basins.
The Andes Cordillera contains the most diverse cryosphere on Earth, including extensive areas covered by seasonal snow, numerous tropical and extratropical glaciers, and many mountain permafrost landforms. Here, we review some recent advances in the study of the main components of the cryosphere in the Andes, and discuss the changes observed in the seasonal snow and permanent ice masses of this region over the past decades. The open access and increasing availability of remote sensing products has produced a substantial improvement in our understanding of the current state and recent changes of the Andean cryosphere, allowing an unprecedented detail in their identification and monitoring at local and regional scales. Analyses of snow cover maps has allowed the identification of seasonal patterns and long term trends in snow accumulation for most of the Andes, with some sectors in central Chile and central-western Argentina showing a clear decline in snowfall and snow persistence since 2010. This recent shortage of mountain snow has caused an extended, severe drought that is unprecedented in the hydrological and climatological records from this region. Together with data from global glacier inventories, detailed inventories at local/regional scales are now also freely available, providing important new information for glaciological, hydrological, and climatological assessments in different sectors of the Andes. Numerous studies largely based on field measurements and/or remote sensing techniques have documented the recent glacier shrinkage throughout the Andes. This observed ice mass loss has put Andean glaciers among the highest contributors to sea level rise per unit area. Other recent studies have focused on rock glaciers, showing that in extensive semi-arid sectors of the Andes these mountain permafrost features contain large reserves of freshwater and may play a crucial role as future climate becomes warmer and drier in this region. Many relevant issues remain to be investigated, however, including an improved estimation of ice volumes at local scales, and detailed assessments of the hydrological significance of the different components of the cryosphere in Andean river basins. The impacts of future climate changes on the Andean cryosphere also need to be studied in more detail, considering the contrasting
Artículo de publicación ISIWe produce the first icefield-wide volume change rate and glacier velocity estimates for the Cordillera Darwin Icefield (CDI), a 2605 km2 temperate icefield in southern Chile (69.6 W, 54.6 S). Velocities are measured from optical and radar imagery between 2001–2011. Thirty-six digital elevation models (DEMs) from ASTER and the SRTM DEM are stacked and a weighted linear regression is applied to elevations on a pixel-by-pixel basis to estimate volume change rates. The CDI lost mass at an average rate of −3.9±1.5 Gt yr−1 between 2000 and 2011, equivalent to a sea level rise (SLR) of 0.01±0.004mmyr−1 and an area-averaged thinning rate of −1.5±0.6mw.e.(water equivalent) yr−1. Thinning is widespread, with concentrations near the front of two northern glaciers (Marinelli, Darwin) and one western (CDI-08) glacier. Thickening is apparent in the south, most notably over the advancing Garibaldi Glacier. The northeastern part of the CDI has an average thinning rate of −1.9±0.7mw.e. yr−1, while the southwestern part has an average thinning rate of −1.0±0.4mw.e. yr−1. Velocities are obtained over many of the CDI glaciers for the first time. We provide a repeat speed time series at the Marinelli Glacier. There we measure maximum front speeds of 7.5±0.2mday−1 in 2001, 9.5±0.6mday−1 in 2003 and 10±0.3mday−1 in 2011. The maintenance of high front speeds from 2001 to 2011 supports the hypothesis that Marinelli is in the retreat phase of the tidewater cycle, with dynamic thinning governed by the fjord bathymetry
The majority of glaciers in central Chile have receded in recent decades, from >50 m to only a few meters per year, mainly in response to an increase in the 08 8C isotherm altitude. The Aconcagua river basin (338 S) is one of the major glaciated basins in central Chile, with 121 km 2 of ice in 2003. An earlier inventory using 1955 aerial photographs yielded a total surface area of 151 km 2 , implying a reduction in glacier area of 20% (0.63 km 2 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. Annals of Glaciology 48 2008
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