Recent Evolution of Glacier Termini in the Tropical Andes of Ecuador

Tropical glaciers are widely recognized as being especially sensitive indicators of climate change. Because the terminus of a tropical glacier typically extends below the 0ºC isotherm year-round, small shifts in mean annual air temperature have persistent impacts on the glacier's equilibrium line altitude. Furthermore, the year-round ablation at the glacier terminus results in a more rapid response to changing energy balance conditions than occurs at glaciers with only seasonal ablation. This is especially true for glaciers in the inner tropics (generally defined as within 5° of the equator), since these areas lack a distinct dry season in which ablation is reduced. Because of difficult access, poor weather, and limited local resources, consistent monitoring of glacier mass balance in the inner tropics has been limited to one site: Glaciar 15 at Volcán Antisana in the tropical Andes of Ecuador. While this program provides invaluable information about climatic change in the tropics, analysis of recent glacier behavior at other locations in Andean Ecuador can better illuminate patterns of spatial homogeneity and heterogeneity in this climatically complex region. Here, we report on the recent evolution of glacier termini at two additional locations in Ecuador: Volcán Chimborazo, located on the southern end of Ecuador's western cordillera, and Volcán Cayambe, at the northern end of Ecuador's eastern cordillera. By comparing digital elevation models (DEMs) derived from 2014 TanDEM-X Synthetic Aperture Radar measurements with DEMs generated in 2017 and 2018 using small unmanned aerial vehicle (UAV) based structure-from-motion photogrammetry, we evaluate changes in both ice surface area and ice surface elevation at the termini of multiple glaciers across Andean Ecuador's distinct east-west precipitation gradient. While limits to UAV capabilities prohibit calculation of whole-glacier geodetic mass balances at these very high elevation sites, these products allow us to quantify, at 12-meter resolution, recent ice volume loss and its spatial variability within single glaciers and across multiple glaciers in the region.