Freshwater calving and anomalous glacier oscillations: recent behaviour of Moreno and Ameghino Glaciers, Patagonia

Moreno Glacier has been consistently advancing during a period of general glacier retreat this century, and has repeatedly dammed an arm of Lago Argentino. The most recent episode of ice-dam failure and catastrophic lake drainage occurred in 1988. However, the recent periodicity of this behaviour has now been interrupted, and the current characteristics of the terminus suggest a future retreat. Because of the nature of calving dynamics, such a retreat would be rapid and irreversible in the short term. Neighbouring Ameghino Glacier, after almost a century of near-stagnation, commenced calving in a newly formed proglacial lake in about 1967 and then retreated 3 km at a mean rate of 334myr -1 for the next nine years in a fashion analagous to that predicted for Moreno Glacier. The behaviour of these glaciers cannot be related directly to regional climate trends; terminus response is more closely controlled by the interplay between calving dynamics and topography. Calving is therefore a potentially significant factor in glacio-climatic reconstruction, even in 'terrestrial' settings.