The last glacial period and its associated glaciation is known in southern Chile as the Llanquihue glaciation (Spanish: Glaciación de Llanquihue). Its area lies west of Llanquihue Lake where various drifts or end moraine systems belonging to the last glacial period have been identified. The glaciation is of the last formations in the Patagonian Ice Sheet. Around Nahuel Huapi Lake the equivalent glaciation is known as the Nahuel Huapi Drift. The preceding interglacial is known as the Valdivia interglacial after its type locality of Valdivia.
General characteristics
The characteristics of the glaciation change according to its latitude. In Central Chile, south of Atacama Desert, the extent of the Llanquihue glaciation was controlled by rain which increases to the southern parts of Chille. The height of the glaciers advances were not the same across the affected area, as they were triggered by north and southward shifts in the moisture-bringing Westerlies and its storm tracks. Glaciers in Central Chile were particularly sensitive to shifts in the precipitation pattern and those to the south in southern Chile (39–43° S) were sensitive to both precipitation and temperature, correlating better with global temperature trends. During large glacier advances the Llanquihue glaciation in Chile showed a marked difference north and south of latitude 41.5° S. To the south Andean valley glacier lobes coalesced and spread out occupying what is today the sea of Chiloé and other marine basins. At times the ice reached all the way across to the foot of the Chilean Coast Range in Chiloé. This meant that the region south of 41.5° S was subject to a proper ice sheet glaciation during large glacier advances. In contrast during times of glacier advance Andean valley glaciers entering the Chilean Central Valley in the Chilean Lake District (39–41.5° S) spread out forming large but separate glacier lobes, meaning that the glaciation remained restricted by topography being a glaciation of valley glaciers, or in other words one of Alpine type. In the Chilean Lake District and Chiloé large outwash plains formed during the Llanquihue glaciation occupies positions between Llanquihue moraines and moraines of the older Santa María glaciation. At present these outwashs contain a distinctive ñadi type soil and vegetation. In the Atacama Desert high mountains (>5000) have remained ice-free through the whole Quaternary period. Similarly the dry areas east of the Andes in Patagonia were not glaciated but developed periglacial features like ice wedges, patterned ground, pingos, rock glaciers, palsas, soil cryoturbation, solifluction deposits during the Llanquihue glaciation. The coast of Chile north of 42° S and most of the Chilean Coast Range remained glacier-free and parts of it also free from periglaciation though the glaciation. Yet, small glaciers existed in the highest part of the Chilean Coast Range. Above altitudes of 100 m (Cordillera Piuchén) or 600 m (Cordillera de Nahuelbuta) soils in the Chilean Coast Range were disturbed by solifluction (a periglacial process). Between 41 and 37° S, the coastal region, the lower slopes of the Chilean Coast Range, and the westernmost Chilean Central Valley remained free of disturbance by the glacial, glacifluvial and periglacial meaning these regions (in particular around Cordillera de Nahuelbuta) served as refugia for Valdivian temperate rainforest. According to Carolina Villagrán the low diversity of bryophytes in Aysén Region when compared to neighboring regions would have been the result of the Llanquihue glaciation covering almost the total of it, leaving little or no space for refugua.
Development of the glaciation Palynological analysis in Chiloé reveal the existence of at least three warm periods, or interstadials, during the Llanquihue glaciation. One interstadial begun 57,000 years before present (yrs BP) and ended no later than 49.000 yrs BP, another that begun 50,000 yrs BP and ended no later than 47,000 yrs BP and a third one from 45,000 to 35,000 yrs BP. During the interstadials of the glaciation the conifers Fitzroya and Pilgerodendron had much greater geographical extent than at present growing during that time in the Chilean Central Valley at latitudes between 41° and 43° S. Between 30 and 40° S glaciers reached their maximum advance about 40 to 35 ka BP, exceeding any extent they had during the global Last Glacial Maximum. Compared to the Llanquihue and Chiloé area maximum glacier advance was achieved much earlier in Torres del Paine and Última Esperanza Sound (51-52° S) where glaciation peaked about 48,000 years ago. There is evidence for five westward advances of glacier lobes in the southern Chilean Lake District and Chiloé (40–42.5° S). These advances occurred at ~33,600, ~30,800, ~26,900, ~26,000 and 17,700–18,100 years before present.
… excerpt ends here. Continue reading the full article.
