Glacial geomorphology of the Pleistocene Lake Fagnano ice lobe, Tierra del Fuego, southern South America.

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

GEOMORPHOLOGY

Elsevier Editorial

Lugar: Amsterdam; Año: 2009 vol. 112 p. 67 - 81

0169-555X

A regional geomorphological study is presented of the southern and eastern coast of Lake Fagnano, one of the most extensive glacial areas of Tierra del Fuego Island, at the southernmost tip of South America. A palaeoglacial reconstruction is made, based on the location of erosional and depositional glacial landforms. The outlet glacier flowing eastwards from the Darwin Cordillera (Fuegian Andes, Chile) had more than 50 tributary glaciers. An alpine-type landscape, including arêtes, cirques, truncated spurs and hanging valleys developed in the western region of the present lake, whereas a piedmont-type landscape including lateral moraines, glaciofluvial and glaciolacustrine terraces and an ice-disintegration landscape developed in the eastern region. The glacier spread over the low ranges and lowlands through three different lobes and was drained by four main outwash basins, directly into the Atlantic Ocean. The ice-covered area is estimated at 4,000 km2; the maximum length of the main lobe at 132 km, and the general slope at 8°. The ice volume, calculated over 1 m wide cross-sections, would have varied between 5,397,092 and 165,722.9 m3. Four terminal positions were recognized and were related to the Inútil Bay and Beagle Channel glacial areas, located to the north and to the south, respectively. Uncalibrated 14C dates on basal peat show that most of the area, especially the easternmost part of the region and the south coast, were free of ice by 12,300 years B.P. Fossil peat contained in the lower basal till deposits yield uncalibrated 14C dates of 31,000–48,200 years B.P. This means that a glacial advance occurred in the area prior to the Last Glacial Maximum (ca. 25,000-23,000 cal. years B.P.).