Last Glaciation landforms in Lake Fagnano ice lobe, Tierra del Fuego,

CORONATO, A.; SEPPÄLÄ, M., RABASSA, J.

Zaragoza, España

Congreso; Sixth International Conference on Geomorphology; 2005

International Association of Geomorphologists

Lake Fagnano (54º33´Lat. S/ 67º14´-68º36´Long. W) fills a huge tectonic depression occupied by a discharge valley glacier, flowing from W to E, during the Last Glaciation. It was 155 km long, 9 km width and 1km thick.  This glacier was receiving over 25 tributary alpine glaciers from both margins, forming also diffluent lobes towards the N and NE, and overflowing the lower hilly system (less than 600 m a.s.l.). In its terminal portion, 35 km eastwards from the present lake heads, the moraines are poorly defined, though till is found on top of bedrock at many sites. The identification of at least five systems of receding moraines along the southern margin of the lake suggests a progressive deglaciation process with periods of ice-front stabilization. The first phase corresponds to an ice-disintegration environment, whereas in the following ones morainic arcs have developed. The lake bathymetry shows topographic irregularities from one coast to the other and two main basins along its longitudinal axis, possibly related to glacial over-excavation of the trough. Drumlinoid landforms, basal, lateral and interlobate moraines, and glaciofluvial and glaciolacustrine landforms and deposits form the southern lake coast. The northern coast presents huge truncated spurs developed on softer marine rocks, and a succession of terraces, probably delta-kames, located at the lateral valleys mouths. Radiocarbon dating of basal peat samples located eastwards of the first Late Glacial ice recession front, indicate that this area was already free of ice around 12,210+/-80 ka B.P.