Search for: All records

Tropical glaciers have retreated over recent decades, but whether the magnitude of this retreat exceeds the bounds of Holocene fluctuations is unclear. We measured cosmogenic beryllium-10 and carbon-14 concentrations in recently exposed bedrock at the margin of four glaciers spanning the tropical Andes to reconstruct their past extents relative to today. Nuclide concentrations are near zero in almost all samples, suggesting that these locations were never exposed during the Holocene. Our data imply that many glaciers in the tropics are probably now smaller than they have been in at least 11,700 years, making the tropics the first large region where this milestone has been documented. 

The glaciers of the Cordillera Blanca, Peru, are rapidly retreating and thinning as a result of climate change, altering the timing, quantity and quality of water available to downstream users. Furthermore, increases in the number and size of proglacial lakes associated with these melting glaciers is increasing potential exposure to glacier lake outburst floods (GLOFs). Understanding how these glaciers are changing and their connection to proglacial lake systems is thus of critical importance. Most satellite data are too coarse for studying small mountain glaciers and are often affected by cloud cover, while traditional airborne photogrammetry and lidar are costly. Recent developments have made unmanned aerial vehicles (UAVs) a viable and potentially transformative method for studying glacier change at high spatial resolution, on demand and at relatively low cost.Using a custom designed hexacopter built for high-altitude (4000–6000 m a. s. l. ) operation, we completed repeat aerial surveys (2014 and 2015) of the debris-covered Llaca Glacier tongue and proglacial lake system. High-resolution orthomosaics (5 cm) and digital elevation models (DEMs) (10 cm) were produced and their accuracy assessed. Analysis of these datasets reveals highly heterogeneous patterns of glacier change. The most rapid areas of ice loss were associated with exposed ice cliffs and meltwater ponds on the glacier surface. Considerable subsidence and low surface velocities were also measured on the sediments within the pro-glacial lake, indicating the presence of extensive regions of buried ice and continued connection to the glacier tongue. Only limited horizontal retreat of the glacier tongue was observed, indicating that measurements of changes in aerial extent alone are inadequate for monitoring changes in glacier ice quantity. 

Abstract. Climate models predict amplified warming at high elevations in low latitudes,making tropical glacierized regions some of the most vulnerable hydrologicalsystems in the world. Observations reveal decreasing streamflow due toretreating glaciers in the Andes, which hold 99% of all tropicalglaciers. However, the timescales over which meltwater contributes tostreamflow and the pathways it takes – surface and subsurface – remainuncertain, hindering our ability to predict how shrinking glaciers willimpact water resources. Two major contributors to this uncertainty are thesparsity of hydrologic measurements in tropical glacierized watersheds andthe complication of hydrograph separation where there is year-round glaciermelt. We address these challenges using a multi-method approach that employsrepeat hydrochemical mixing model analysis, hydroclimatic time seriesanalysis, and integrated watershed modeling. Each of these approachesinterrogates distinct timescale relationships among meltwater, groundwater,and stream discharge. Our results challenge the commonly held conceptualmodel that glaciers buffer discharge variability. Instead, in a subhumidwatershed on Volcán Chimborazo, Ecuador, glacier melt drives nearly allthe variability in discharge (Pearson correlation coefficient of 0.89 insimulations), with glaciers contributing a broad range of 20%–60%or wider of discharge, mostly (86%) through surface runoff on hourlytimescales, but also through infiltration that increases annual groundwatercontributions by nearly 20%. We further found that rainfall may enhanceglacier melt contributions to discharge at timescales that complement glaciermelt production, possibly explaining why minimum discharge occurred at thestudy site during warm but dry El Niño conditions, which typicallyheighten melt in the Andes. Our findings caution against extrapolations fromisolated measurements: stream discharge and glacier melt contributions intropical glacierized systems can change substantially at hourly tointerannual timescales, due to climatic variability and surface to subsurfaceflow processes.