Onelli Glacier retreat separation, Argentina

The Onelli Glacier drains eastward from the South Patagonia Icefield into Lago Onelli (LO), which then connects to Lago Argentino (LA). Lago Onelli has three main glaciers termininating in the lake Aggassiz (A), Onelli(O)and Bolados Glacier (B). The glacier is noted as 13 km long with an area of 84 square kilometers by the Labratorio de Glaciologia in Chile . Warren and Sugden (1993) note an 1800 meter retreat from 1945-1992 for Onelli Glacier and 850 meters for Agassiz Glacier. Eric Shipton was the first to visit this glacier and did so in the company of Ohio State glaciologist John Mercer in 1958. They found Lago Onelli so filled with icebergs that little water could be seen (Shipton, Land of Tempest, 1963). Agassiz and Onelli Glacier were observed to have a shared terminus much like Onelli Glacier and Belados Glacier in 2003, ion contact but one flowing into the fjord from the north with a steep calving face, and one from the northwest (Onelli) with a gentler slope. The focus for Mercer was the age of the moraines beyond the glacier terminus, for Shipton hiking up onto the icefield to explore potential avenues to the crest of the icefield. The glacier is located on the icefield base map image from the Glaciares of Argenina website. . A comparsion of Landsat satellite images indicate the separation and retreat of Bolados (B) and Onelli Glacier(O) from 2000-2010. In 2000 the joint terminus cuts directly across Lago Onelli as one reasonably straight 1.6 km long. By 2003 the glaciers are barely touching and the combined termini are now long 1.8 km long. BY 2008 the glaciers are separated by 1300 meters. The retreat from the 2000 terminus of Onelli Glacier has been 1500-1800 meters depending where on the ice front the retreat is assessed. Theretreat of the last decade of 160 meter/year is a considerable acceleration over the period from 1945-1990. Belados Glacier has retreated 800 meters. The ELA in the satellite images from recent years has been 1300 meters.


Tyndall Glacier, Chile Retreat Continues

Tyndall Glacier is a large outlet glacier of the Southern Patagonia Icefield (SPI). This glacier has an area of over 300 square kilometers. The main glacier terminus ends in Lago Geikie, which began to form around 1940, and the east terminus previously terminated in Lago Tyndall. Raymond et al (2005) report that the glacier had receded 5 km from 1945 to 2001. The retreat is illustrated in a figure from Rivera & Casassa (2004). This web page on the Tyndall Glacier is one of many provided by Andrés Rivera at the Laboratorio de Glaciología at Universidad de Chile. Assessing the ice surface elevation changes on three profiles 8-15 km above the terminus, the amount of thinning was determined by Raymond et al (2005). From 1945-2002 the average thinning rate of the glacier at meters was 2.3 meters per year. The rate has accelerated averaging over 3.3 meters per year since 1985. This has driven the retreat. Lago Geikie is a deep lake with maximum depths reaching 400 meters and was 300 meters at the calving front in 2001 Raymond et al (2005) . This allows for considerable calving of the thick Tyndall Glacier, which is grounded on the bottom of the lake at its terminus. The glacier velocity near the calving front is 700 meters per year. A comparison of the terminus position from the aforementioned papers, Google Earth from 2003 (top Image) and a Geoeye image from 2010 (bottom image) indicates the changes of Tyndall Glacier are ongoing. Lago Tyndall (LT) for example is continuing to contract as the terminus (TE) that feeds it has thinned and pulled back from the valley that feeds it. Increasingly this is becoming a watershed that will not be fed by Tyndall Glacier. Lago Geikie (LG) continues to expand now 7 km long. The retreat in the last 7 seven years has been 600-900 m on the main calving front. This has exposed a new peninsula (P). The glacier terminus is much narrower than in 1975 in an aerial image from Raymond et al (2005). The snowline on the glacier is at 900 meters and there is considerable glacier area above 1200 meters, indicating this glacier can survive additional warming, note the above image. As Raymond et al (2005) emphasized the glacier bottom remains below the Lago Geikie lake level for 14 km. Over much of this distance calving would play a role, helping continue the recent retreat. This retreat due to calving into a glacier lake resulting from ongoing glacier thinning resulting from increased surface ablation is widespread from Bear Glacier, Gilkey Glacier and Yakutat Glacier in Alaska, to Tasman Glacier in NZ to Nef Glacier and Colonia Glacier in