Quaternary Glacial History of the Chilean Andes Presented by Calvin Wight

Outline Background Controls on Glaciation – Climatic – Tectonic – Latitudinal Glacial History of the Chilean Andes – Northern – Central – Southern

Background Andes: a Mesozoic-Tertiary orogenic belt trending from north to south and form the spine of South America Span from subpolar (56˚S) to warm tropical (18˚S) regions Observations of glaciation recorded since Charles Darwin’s 1830’s circumnavigation in the HMS Beagle

Time Scale Ma 0.01 Ma Present

Controls on Glaciation Regional Climate Tectonics (Altitude) Latitude (Polar  Warm Temperate)

Regional Climate Precipitation regimes Westerly vs tropical wind belts Temperatures

Tectonics Controlling factor on elevation Plays a large role forming in climatic barriers (i.e. orogenic deserts)

Latitude Lower Latitudes (closer to the equator) will be home to inherently warmer climates, so elevation will play a greater role Higher latitudes (more polar) will have cooler climates, and fewer constraints on glacial extents

Quaternary Glacial History of the Chilean Andes Lines of evidence used in this study Northern Andes Central Andes Southern Andes

Lines of Evidence for Glacial Intervals Morphology of glacial deposits Equilibrium Line Altitudes Dating Techniques: both quantitative and relative Comparative Weathering  older deposits will have undergone more weathering

Equilibrium Line Altitudes and Topography of the Chilean Andes Average topography along Chilean Andes from 18˚-51˚S with estimate of modern glacial Equilibrium Line Altitude from Clapperton, 1994.

Northern Chilean Andes 18˚30’S – 27˚S Hyper arid high elevation environment Separated by South American Dry Diagonal – Northern: 18˚30’–26˚S – Southern: 26˚-29˚S Lies within transition zone between tropics and westerly wind belts – Tropical: summer precipitation – Westerly: winter precipitation

Just how dry is this place?

“Northern Northern” Chilean Andes 18˚30’–26˚S Comprised of individual tall volcanic cones Most of the region glaciated in the late Pleistocene Debate over “cool” vs “humid” hypothesis – Reconstructed ELA below volcanic peaks indicates humidity to be the limiting factor In moraines, underlying peat and overlying volcanic debris dated to 13,500-12, C years BP for last glaciation

“Southern Northern” Chilean Andes 26˚-29˚S Large mountain ranges and deep valleys  change in glacial attributes Steep ELA gradient (800m) decreasing from north to south Glaciation is humidity dependent, due to lowering ELA from latitudinal position  northward migration of westerlies

Northern Chilean Glaciation Lateral moraines depict three stages of glaciation in the late Pleistocene Glacial characteristics change with topography from high elevation individual volcanic cones to mountain range-valley topography Aridity implies that humidity is the major limiting factor in glaciations

Central Chilean Andes 29˚- 33˚S Transitional Zone between subtropical- temperate climates Topographically high regions with net precipitation increasing from north to south Two basins: Rio Aconcagua and Rio Elqui basin

Central Andes (herd of alpaca for scale)

Central Andean Glacial Indicators Rio Elqui Basin (30˚S): evidence of two glacial stages exist from weathered moraines Rio Aconcagua basin (33˚S): at least three major glacial stages are apparent from moraines ELA slopes upwards from west to east Suggests that glacier expansions in the region are a product of increasing precipitation regimes from a northward shift in the westerlies

Central Andean Glacial Chronology Three observed moraine stages mark glacial intervals in Central Chilean Andes Ages of morainal drifts: – Penitentes- >40,000 yr BP ( 230 Th/ 232 Th and U- series) – Horocenes- late Pleistocene (unweathered till, fresh morphology) – Almacenes- late-glacial, farther up valley (14, ,000 yr BP)

Southern Chilean Andes 33˚-56˚S Much of Andean highland lies above 4000m Undergone extensive Pleistocene glaciation 33˚-37˚S not widely studied due to Holocene volcanism covering glacial deposits Region de los Lagos (39˚-42˚S) is the most widely studied due to well exposed glacial morphologic deposits

Region de los Lagos (Lake District)

Greatest Evidence for Pleistocene Glaciation Four mappable drift sheets composed of till and outwash within Lago Llanquihue basin Drifts from youngest to oldest: – Llanhique – Santa Maria – Rio Llíco – Caracol

Drift extent mapped by Porter, 1981.

Llanqihue Drift Last major expansion of Andean glacial system composed of three episodes of glacial advance Llanquihue I- 58,000-30,000 yr BP Llanqihue II- 20,000-19,000 yr BP Llanqihue III- 15, ,200 yr BP

Santa Maria Drift Western extent parallels that of the Rio Llíco Drift Broad piedmont glacial system Contains three end moraine systems depicting a multifaceted ice advance

Rio Llíco Drift Greatest glacial extent recorded in the Region de los Lagos Moraines exceed limitations of radiocarbon dating Paleomagnetic analysis of silts depict normal polarity, but are potentially unreliable.

Caracol Drift Ice spread westward as a piedmont glacier Rose on east slope of coastal mountains Less extensive than Rio Llico Drift

Drift extent from Porter, 1981’

Region de los Lagos

Region de los Lagos Last Andean glaciation confined in the mountains north of the Lake District Multiple glacial advances produced piedmont lobes within the Lake District as ELA lowered Post Llanqihue recession has not been studied in detail

South of Region de los Lagos Extensive mountain glacier system extended out onto the continental shelf As the Llanqihue system receded at the end of the Pleistocene, calving occurred potentially similar to what is seen presently in Glacier Bay, Alaska

Glacier Bay, Alaska

Summary Quaternary Andean glaciation is highly variable depending on tectonics, climate, and latitude. Northern Andes: hyper arid high elevation, three late Pleistocene glaciations recorded Central Andes: more temperate climate, still humidity dependent, three glacial stages recorded between two basins Southern Andes: extensive glaciation recorded in drift sheets and morainal deposits, a multitude of glacial advances at the end of the Pleistocene.

Greater Importance? Chilean Andes represent the most extensive and detailed record of glaciation in the southern hemisphere Spans across multiple climatic zones Significant for global paleoclimate reconstructions

References -Ammann, C.M., B. Jenny, K. Kammer, and B. Messerli, 2001: Late Quaternary Glacier response to humidity changes in the Arid Andes of Chile (18-29°S). Palaeogeography Palaeoclimatology Palaeoecology, v. 172, p Clapperton, C.M., 1994: The quaternary glaciation of Chile: a review. Revista Chilena de Historia Natural. v. 67, p Geyh, M.A., M. Grosjean, L. Núñez, and U. Schotterer, 1998: Radiocarbon reservoir effect and the timing of the Late-Glacial/Early Holocene humid phase in the Atacama Desert (Northern Chile). Quaternary Research, v. 52, p Gregory-Wodzicki, K.M., 2000: Uplift history of the Central and Northern Andes: A review. Geological Society of America Bulletin, v. 112, p Grosjean M., M.A. Geyh, B. Messerli, H. Schreier, and H. Veit, 1998: A Alte Holocene (<2600 BP) glacial advance in the south- central Andes (29°S) northern Chile. The Holocene, v. 8, p Heusser, C.J., 1977: Quaternary glaciations and environments of northern Isla Chiloé, Chile. Geology, v. 5, p Hirakawa, K., M. Nogami, T. Imaizumi and A. Okada, 2000: Some basic data on the quaternary glaciation in the Chilean Lake District. Geographical Reports of Tokyo Metropolitan University, v. 35, p Hubbard, A.L., 1997: Modeling climate, topography and palaeoglacier fluctuations in the Chilean Andes. Earth Surface Proceses and Landforms, v. 22, p Moreno, P.I., G.L. Jacobson Jr., T.V. Lowell, and G.H. Denton, 2001: Interhemispheric climate links revealed by a late-glacial cooling episode in southern Chile. Nature, v. 409, p Porter, J.C., 1981: Pleistocene Glaciation in Chile. Quaternery Research, v. 16, p

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