Equilibrium Line Altitudes of Late Pleistocene and Recent Glaciers in Central Mexico

Existing and former equilibrium line altitudes (ELAs) are calculated for present and past glaciers on volcanoes Iztaccíhuatl and Popocatépetl at east edge of. and Ajusco at southwest edge of Cuenca de México, central Mexico, at 19° N.; they indicate present (1953) ELA for Iztaccíhuatl is 4880 m, for Popocatépetl 4925 m, but Ajusco is below snowline. ELAs for past substages of glaciation on Iztaccíhuatl were 1370 m below present ELA (during Tomicoxco Substage), 100 m below (Diamantes First Advance), 910 m below (Diamantes Second Advance), about 720 m below (Alcalican I), about 630 m below (Alcalican II), and 245 m below (Ayolotepito Stade). Mid-Neoglaciation ELA on Popocatépetl was 195 m below present ELA, and Late Neoglaciation (1906) ELA 90 m below. ELAs for past Ajusco glacial substages imitate those on Iztaccíhuatl but are 700-800 m lower. Late Pleistocene and Recent temperature coolings to accomplish these glaciations are about 8°C during probable Bull Lake equivalents, about 6°, 5°, and 4°C during Pinedale equivalents, and about 1.5° to 0.5°C during Neoglaciation Stades.