On Glaciation of the Southern Andes with Special Reference to the Penı´Nsula De Taitao and Adjacent Andean Cordillera (,468300S)

Journal of South American Earth Sciences 15 (2002) 577–589 www.elsevier.com/locate/jsames

On glaciation of the southern Andes with special reference to the Penı´nsula de Taitao and adjacent Andean cordillera (,468300s)

C.J. Heusser

Heusser and Heusser, 100 Clinton Road, Tuxedo, NY 10987, USA

Received 1 May 2002; accepted 1 June 2002

Abstract Ice fronts in the southern Andes during late Wisconsin–Weichselian glaciation reached maxima early and late in oxygen isotope stage 2. 14 14 The first maximum occurred between 29,400 and 22,300 CyrBP, and the second is centered around 15,000 CyrBP. Glaciers at different latitudes varied in size, apparently in response to maximum levels of precipitation from the moisture-bearing southern Westerlies. Following 14 deglaciation, which was reached in the interior midlatitude cordillera earlier than 12,300 CyrBP, a late glacial readvance of Younger Dryas age is indicated by an increasing number of glacial geomorphic and paleoecological records, but it remains controversial. During stage 2, the cordillera supported a complex of ice caps and valley glaciers. On the Penıńsula de Taitao and to the south, glaciers reaching low altitudes were evidently small compared with the large piedmont lobes that covered the sector encompassing the Regioń de los Lagos–Isla Grande de Chiloe´ to the north. Flowing from an icecap on Taitao, valley glaciers became coalesced only locally, thereby giving rise to small piedmont lobes. Adjacent to Taitao in the Andes, where there is little studied evidence of stage 2 glaciation, the oldest dated advances appear to be late Holocene. Glaciers at this latitude, situated in the Tres Montes fracture zone at the Antarctic–Nazca–South American triple plate junction, have been subjected to tectonic activity. q 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Glaciation; Southern Andes; Glacial limits

1. Introduction netic measurements have revealed a range of contrasting ages for glacial drift that was believed by Caldenius (1932) Hollin and Schilling (1981), in their chapter ‘Late to be chronostratigraphic, which thus invalidates the Wisconsin–Weichselian Mountain Glaciers and Small Ice premise of correlation over vast sections of the cordillera. Caps’ in the Last Great Ice Sheets, presented an outline map A review of the latest literature presented herein seems (Fig. 1) that, despite its limitations, has served as a working timely to update the mapping and chronology of glaciation base for defining late Pleistocene glacial limits in the and assess the general character of the ice cover. The focus southern Andes. The extent of glaciation was generalized is on the most recent results of studies principally in the because of stratigraphic and chronological constraints. The northern and southern parts of the southern Andes; other reviews by Mercer (1976) and Paskoff (1977) provided the work from intervening latitudes has proved less informative. comparatively few records presenting significant data. Their An interpretation of aerial photographs of the Penıńsula de concern regarding regional tectonism and synchrony of Taitao (Table 1) given here offers a view of glacial glaciation notwithstanding, Hollin and Schilling (1981),in conditions along the essentially data-poor Pacific coast. setting limits, relied heavily on the mapping accomplished The nearby triple junction of the South American, Nazca, in Fuego-Patagonia by Caldenius (1932). His Gotiglacial and Antarctic plates suggests a possible connection between limit south of 508S and Finiglacial limit north of 508S were tectonism and climate with regard to an unusual record of used to approximate the locations of ice margins most Taitao glacier fluctuations. In the Andes adjacent to the closely. As pointed out by Rabassa and Clapperton (1990) Penıńsula de Taitao, tectonism also appears to have had a and Clapperton (1993), radioisotope dating and paleomag- coincident role, where glaciers coming out of the Campos de Hielo del San Valentıń (northern part of Hielo Patagońico E-mail address: [email protected] (C.J. Heusser). Norte, Fig. 1) have undergone significant advances.

Fig. 1. Estimated late Wisconsin–Weichselian ice margins in the southern Andes according to Hollin and Schilling (1981). Major existing iceﬁelds are shown stippled. C.J. Heusser / Journal of South American Earth Sciences 15 (2002) 577–589 579

14 Table 1 readvance between 11,400 and 10,200 CyrBP at the time Aerial photographic coverage provided by the US Army Air Force 1944/45 of the European Younger Dryas chronozone. Climatic of Penıńsula de Taitao and adjoining Andes (Instituto Geogra´fico Militar, trends shown by paleoecological reconstructions for the Santiago, Chile) Regioń de los Lagos–Isla Grande de Chiloe´ broadly parallel Locations, sorties, and exposures intervals of glacial advance and retreat believed to be as old as OIS 4 (Heusser et al., 1999). Brazo Norte–Brazo Nor Poniente: 456.L.(185–192) In the southernmost Andes (Fig. 1), the record produced Brazo Desague: 456.R.(186–188); 456.V.(186–189); 555.L.(79–81); by glaciers issuing principally from the Cordillera Darwin 555.R.(81–83) 0 Brazo Oriental: 456.R.(183–185) (54835 S) is the result of considerable study. A piedmont Brazo Sur Oriental: 456.L.(182–183); 456.R.(179–182); 456.V.(180– lobe during early OIS 2 after about 27,790 and before 14 183); 555.R.90 23,590 CyrBP spread northward some 200 km in the Brazo Sur: 456.L.(175–181); 456.R.(177–178); 456.V.(176–179) Estrecho de Magallanes and branched eastward into Bahıá Laguna Elena: 456.L.(34–38); 456.V.(33–35) Inu´til (Clapperton et al., 1995). During late OIS 2, a Laguna Elena, Fiordo Newman sector: 408.L.(113–116); 408.R.(107– 114); 408.V.(109–114); 455.R.158; 456.R.(34–37) minimum date for subsequent full glacial advance in the Laguna San Rafael: 555.L.(88–92); 558.L.(32–38); 456.R.(175–176) vicinity of the outermost stand of the lobe, approximately 14 Golfo Elefantes: 555.L.(82–87); 558.L.(39–44) 175 km from the Cordillera Darwin, is 14,990 CyrBP 14 Glaciar San Quintıń: 555.L.(93–99); 558.L.(26–31); 456.R.(173–174) (Ashworth et al., 1991); another date of 14,260 CyrBP Glaciar Gualas–Glaciar Reicher: 558.R.39 (McCulloch and Bentley, 1998) comes from a site within 100 km of the cordillera. In addition, reevaluation of the 2. Late Wisconsin–Weichselian glaciation of the chronology at Puerto del Hambre (568360S) provides a 14 southern Andes: an overview minimum date of 14,455 CyrBP (Heusser et al., 2000), invalidating older dates of 15,800, 16,590 and 16,290 14Cyr Glacial limits in various sectors of the Andes have been BP at the site (Heusser, 1983; Porter et al., 1992; McCulloch established with greater certainty over the past two decades and Bentley, 1998). The older dates are from samples following the estimate of ice margins outlined by Hollin and believed to be contaminated by Tertiary-age carbon Schilling (1981). In the process, the timing of glacial events (Heusser, 1999). Subsequent late glacial advance is 14 has reached a point at which regional correlation has bracketed by 12,010 and 10,050 CyrBP (McCulloch become increasingly implicit. At midlatitude (408350 – and Bentley, 1998). Justification for its possible Younger 428250S), special attention has been given to the Regioń Dryas age is found in the paleoecological record at Puerto de los Lagos–Isla Grande de Chiloe´ (Fig. 1). Detailed del Hambre (Heusser et al., 2000). glacial geomorphic maps of Llanquihue drift (Andersen Traveling eastward from the Cordillera Darwin, a valley et al., 1999) record the presence of piedmont lobes that glacier in Canal Beagle (548550S) during late OIS 2 pushed westward to form a well-defined moraine belt west terminated just beyond the eastern entrance to the canal of Lago Puyehue, Lago Rupanco, and Lago Llanquihue and (Moat glaciation of Rabassa et al., 1990a). Aerial photo- the marine waterways of Seno Reloncavı´, Golfo de Ancud, graphs show the extent of the end moraine of the glacier and Golfo Corcovado. Lobe formation became accentuated along eastern Isla Navarino, on adjacent Isla Picton, and at by advances of the ice early and late in oxygen isotope stage Punta Moat on Isla Grande de Tierra del Fuego. A limiting 14 14 2 (OIS 2) between 29,400 and 22,300 CyrBP and 14,900– date of 14,640 CyrBP for the moraine comes from a point 14 14 14,550 CyrBP; an advance at 22,600–22,300 CyrBP along the canal where the ice front stood, approximately was apparently of maximum proportions in the north, 25 km from its terminal location, during recession (Heusser, whereas in the south, the maximum was reached between 1998). What Caldenius (1932) originally identified as an 14 14,900 and 14,800 CyrBP (Denton et al., 1999a,b). The end moraine on nearby Isla Gable has been shown to be a difference in size and timing of maxima at different latitudes drumlin field (Rabassa et al., 1990b). Deglaciation of Canal in the cordillera is attributed to a variable equatorward shift Beagle in proximity to the Cordillera Darwin dates to 14 in intensity of the storm systems of the southern Westerlies approximately 9000 CyrBP (Coronato, 1995). during OIS 2 (see Lamy et al., 2000). Earlier than 29,400 to Fluctuations of glaciers draining the southern part of the 14 .40,000 CyrBP, a lengthy interstade in this time frame Hielo Patagońico Sur (Fig. 1) produced several moraines, of (OIS 3) is implied by the lack of significant glacial evidence. which only those of late glacial and younger age are dated Deglaciation, with the lobes pulling back into the (Marden and Clapperton, 1995; Marden, 1997). Another cordillera, followed the full glacial. Altitudes above 700 m case within the time frame of the Younger Dryas 14 in the nearby Andes were free of ice before 12,300 CyrBP chronozone is the advance of Glaciar Grey (518S) with 0 14 (Heusser et al., 1992). At Lago Mascardi (41817 S), locally limiting dates of 11,880 and 9180 CyrBP. Along the situated in the Argentine Andes (Ariztegui et al., 1997), eastern border of the Hielo Patagońico Sur to the north grain-size and hydrogen index values, among fossil pollen (,508S) at Lago Viedma and Lago Argentino, moraines 14 and chironomid core data, indicate wastage of the ice until with minimum dates of 9588 and 9482 CyrBP, including 14 14 around 12,400 CyrBP and subsequent peak glacial a moraine dated 10,000 CyrBP at Punta Bandera (Mercer, 580 ..Husr/Junlo ot mrcnErhSine 5(02 577–589 (2002) 15 Sciences Earth American South of Journal / Heusser C.J.

Fig. 2. Extent of glaciation of southeastern Penıńsula de Taitao early and late in oxygen isotope stage 2 (OIS 2), as interpreted from US Army Air Force aerial photography 1944/45. For sources of locations of Te´mpanos and related moraines beyond the Andean mountain front, see the text. Base map with altitudes in meters is from the Servicio Nacional de Geologıá y Minerıá (1982). Area of coverage is shown in Fig. 1. C.J. Heusser / Journal of South American Earth Sciences 15 (2002) 577–589 581

Fig. 3. Locations of Sites 1 and 2 (Fig. 2) at altitudes of approximately 20 m, according to Lumley (1993), at the entrance of Brazo Norte (right) and along Brazo Desague (lower right), Lago Presidente Rı´os, Penı´nsula de Taitao (USAAF 456.L.185).

14 1976), are also believed to be Younger Dryas age (Wenzens, date of 14,355 CyrBP (Lumley and Switsur, 1993). At 1999). The Younger Dryas equivalent age of the Punta scattered locations in the Archipie´lago de los Chonos to the Bandera moraine also comes from a date of 10,930 14Cyr north (448190 –448530S), glaciation is limited by deglacial 14 BP; older Punta Bandera moraines date to 13,000 and 11,100 dates of 13,560, 13,480, 13,320, and 13,230 CyrBP 14 CyrBP (Strelin and Malagnino, 2000). (Haberle and Lumley, 1998). Late glacial moraines formed The glacial limit on the Pacific side of the cordillera by glaciers emanating from the Hielo Patagońico Sur in the between Isla Grande de Chiloe´ and Isla Grande de Tierra del Regioń de los Canales to the south, according to Mercer 14 Fuego (Fig. 1) remains virtually unknown. That it existed as (1970), are dated close to 11,100 CyrBP at Glaciar 0 14 an unbroken cover of ice, as drawn by Hollin and Schilling Te´mpano (48845 S) and 10,000 CyrBP at Glaciar (1981), is purely conjectural. Changing patterns of atmos- Bernardo (488350S). At Puerto Edeń (498080S), a crescentic pheric moisture, from latitudinal movement in the main multiple end moraine about 20 m high, positioned by a thrust of the southern Westerlies, resulted in what was valley glacier descending from the heights of Isla Well- 14 apparently a highly variable glacier complex. Throughout ington, was first given a minimum date of 9670 CyrBP the complex, valley glaciers radiating from ice caps of (Mercer, 1970), but now appears to be older than 12,960 14C differential area and thickness coalesced as piedmont lobes yr BP (Ashworth et al., 1991). at or near tide level. Compared with maxima at the time of Overall, important advances of glaciers, according to the OIS 2, available data indicate that the cordilleran glacier foregoing chronological evidence, are recorded both early complex was of a greater dimension during early Wiscon- and late in OIS 2 with a subsequent advance of smaller sin–Weichselian glaciation, that is, at the time of OIS 4. dimension in the late glacial. Ice fronts early in OIS 2 were 14 On the Penıńsula de Taitao (,468S), a locally developed at maxima between 29,400 and 22,300 CyrBP ice cap was the source of valley glaciers with a minimum (Clapperton et al., 1995; Denton et al., 1999a,b). The 582 C.J. Heusser / Journal of South American Earth Sciences 15 (2002) 577–589 C.J. Heusser / Journal of South American Earth Sciences 15 (2002) 577–589 583

14 14 maximum set between 14,900 and 14,550 CyrBP in late of the basin; another date of 14,100 CyrBP at Site 2, OIS 2 (Denton et al., 1999a,b) may have had its start earlier, where Brazo Norte joins Brazo Desague, is extrapolated an implication based on several sources in the cordillera. from a linear interpolation model (Lumley, 1993). Terminal Limiting the maximum are unpublished dates from lacus- areas and the lateral extent of glaciers indicated outside the trine sediments at depth in a core of a mire at Mayol on arms of the lake early and late in OIS 2, as shown by aerial eastern Isla Grande de Chiloe´ (Heusser et al., 1999): photography (Table 1), are presumed to follow the pattern 15,297 ^ 114 (AA18099, 377–379 cm), 15,250 ^ 140 set in the Regioń de los Lagos and Estrecho de Magallanes 14 (AA18100, 379–381 cm), and 15,501 ^ 129 CyrBP (Fig. 1). Ice fronts on the Penıńsula de Taitao during early (AA18101, 381–383 cm); Lago Mascardi, Argentine OIS 2 are assumed to have stood farther forward than they 14 Andes, at 15,250 CyrBP (Ariztegui et al., 1997); and did in late OIS 2. 14 Estrecho de Magallanes at 14,990 CyrBP (Ashworth et al., 1991). A readvance at a time corresponding to the Younger 3.1. Brazo Desague Dryas chronozone is supported by an increasing number of glacial geomorphic and paleoecological observations (Ariz- Two distinct ice front locations are recognizable 10 km tegui et al., 1997; Marden, 1997; McCulloch and Bentley, northeast of the end of the arm. A remnant morainal arc 1998; Heusser et al., 1999, 2000; Strelin and Malagnino, crosses the lower Rıó Presidente Rıós, where the river 2000). That atmospheric cooling affected the advance, as it broadens upstream from an outer moraine belt. The outer did at higher latitudes of the north Atlantic, remains a belt, when first encountered during early exploration, was subject of controversy. Bennett et al. (2000), in what may be described by Grosse (1990) as typical glacial topography, considered a view biased toward selective evidence, find no similar to terrain in the vicinity of Istmo de Ofqui to the basis for recognizing the Younger Dryas in southern Chile. south (Fig. 2). The glacier at the time the outer belt was formed apparently received additional nourishment from tributary ice coming from cirques along the upper north side 3. Penıńsula de Taitao of the valley. The ridge top above cirque headwalls reaches an altitude of 971 m. Penıńsula de Taitao and the contiguous drowned lowland to the east (Fig. 2) mark the southern extremities, 3.2. Brazo Oriental respectively, of the Cordillera de la Costa and Valle Central of lower latitudes. Altitudes in the north of the peninsula rise End moraines are conspicuous in the terminal area no to just over 1300 m and in the south are seldom more than more than a few kilometers from shore, their limits traceable 500 m. Lago Presidente Rıós, much branched and near sea upvalley as trimlines along the southern slope. The level, is the prominent feature in the central interior. The moraines fronting Brazo Oriental have been breached by a lake, which rests in a glacially eroded valley network and stream that was active when the lake level was higher. conforms to a regional fracture pattern, cuts across bedrock Abandoned now, the stream traveled a course downvalley at the boundary between pre-Jurassic metamorphic base- through an area of outwash as it passed eastward. ment and Patagonian batholith of Jurassic and younger age (Forsythe and Nelson, 1985). Bedrock in the low-lying eastern part of the peninsula is buried beneath undiffer- 3.3. Brazo Sur Oriental entiated glacial drift (Servicio Nacional de Geologıáy Minerıá, 1982). At altitudes below 200 m, mostly in the As in the case of Brazo Oriental, a moraine belt of the south and east, dense rain forest in a hyperhumid oceanic latest glacial advance lies in proximity to the southern end climate has generally overgrown and obscured landforms of the arm (Fig. 4). To the southeast is a network of braided produced at the time of glaciation. Above 200 m, with the outwash channels associated with an outer belt recognized tree line at 600 m (Lumley, 1993), glacial features become in the upper reaches of the Rıó Negro by Keller (1949). more visible in the open arboreal vegetation. Moraines bordering the arm and at the distal edge of the Valley glaciers stemming from an ice cap on the heights outwash rise upward along the sides of the valley. Well- of the peninsula in OIS 2 flowed southward and eastward in developed on the west-facing slope, small lakes are the the basin of Lago Presidente Rıós. The age of glaciation is result of impoundment by the ice. Trimlines clearly define 14 implied from the minimal deglacial date of 14,355 CyrBP glacial limits along the ridge separating Brazo Sur Oriental at Site 1 on Brazo Norte (Fig. 3), located in the central part from Brazo Oriental.

Fig. 4. End moraines and associated braided outwash shown are at the foot of Brazo Sur Oriental, Lago Presidente Rı´os, Penı´nsula de Taitao. Upvalley on the west-facing slope, the latest sets of moraines, each fronted by proglacial lakes, are interpreted to mark outer and inner glacier limits, respectively, during early and late OIS 2. Ice levels (lateral moraines and trimlines, upper right) are visible where the glacier branched at the junction of Brazo Sur Oriental and Brazo Oriental (USAAF 456.V.181 and 183). 584 C.J. Heusser / Journal of South American Earth Sciences 15 (2002) 577–589 C.J. Heusser / Journal of South American Earth Sciences 15 (2002) 577–589 585

3.4. Brazo Sur of the glacier. These include inter alia temperature and snowfall fluctuations in the accumulation zone coincident Glaciation in the southeastern part of the peninsula with a greater altitude of the source region at 1200 m, in appears to have been comparatively far reaching. A moraine contrast with conditions at lower altitudes around Lago rims the foot of Brazo Sur, beyond which is a broad stretch Presidente Rıós. The virtually straight, unbranched align- of channeled outwash bounded by morainal ridges and older ment of the basin also proved advantageous, in that it drift and collected by the Rıó Man˜iuales. The drift border, presented an unimpeded avenue for changes in regimen shown as it connects with drift to the west (Fig. 2), is upglacier to be translated directly downvalley. kilometers across, but boundaries are uncertain. Equally Two additional factors may have played a role in causing uncertain is where drift from the peninsula meets undiffer- the glacier to pulsate during recession. The first is the entiated drift presumed to belong to OIS 4 and older stages amount and rate of isostatic rebound of the metamorphic in the lowland to the east. Chaotic drainage patterns of well- basement, which, being elevated stepwise into the accumu- developed neighboring Rıó San Tadeo in the south appear to lation zone, resulted in episodes of glacier rejuvenation. The reflect the extent of subsidence, including drowning of other pertains to a similar effect caused by tectonic forests by the tide, as observed regionally by Simpson movement at the triple plate junction, where the Chile (1875), Bird (1938), Heusser (1960), and Reed et al. (1988), Rise, bound by the Tres Montes and Taitao fracture zones, among others. From a source in the vicinity of Penıńsula actively collides with the continental margin (Forsythe and Esmeralda (Fig. 2, indicated by arrows), glaciers apparently Nelson, 1985; Forsythe et al., 1986). Positioned in the Tres have been in contact with ice from the Taitao interior. Montes fracture zone, the Penıńsula de Taitao has been subject to crustal deformation during the late Tertiary and 3.5. Laguna Elena Quaternary.

West of Brazo Sur, glaciers draining 37 km long Laguna 3.6. Laguna Newman Elena, as well as three other proximal valleys, produced unusual recessional sequences (Fig. 5). Lobes adjoining one Glaciers west of Laguna Elena spread southwestward another expanded to form a common front across the toward the Golfo Tres Montes. Their limits at Laguna transverse lowland over a distance of 15 km. Beyond Newman, though not clearly definable for the most part, Laguna Elena, as indicated by Bru¨ggen (1950), an outer appear to have been reached a short distance beyond the moraine several kilometers distant directs the course of Rıó south end of the lake. Beyond the lake and for approxi- Aldunate. Within approximately a kilometer of the lake mately 10 km to the east, moraines marking the outer and shore, a set of inner moraines in close order behind an apron inner ice margins are distinctly lobate in outline (Fig. 2). of strongly braided outwash conforms to embayments at the Drift outside the moraines, pocketed by many small lakes, end of the lake. At least 12 definitive arcs are recognizable, appears to be largely glaciofluvial. their size and definition reduced laterally to depositional traces associated with stream courses along the sides of the valley. The formidable size of the Laguna Elena inner set 4. Adjacent Andean cordillera probably derives from the location of the lake, which is almost entirely underlain by readily abraded metamorphic The Cordillera de los Andes (Fig. 2) rises abruptly east of bedrock. Glaciers scouring the more obdurate crystalline the Penıńsula de Taitao. Along an active scarp of the rock of the Patagonian batholith in the basin of Lago Liquin˜e–Ofqui fault, the mountain mass, in less than 5 km, Presidente Rıós, by comparison, developed moraines of steeply elevates to altitudes of more than 1400 m (Reed lesser magnitude. et al., 1988). The interior is dominated by Monte San The multiple moraines at Laguna Elena, which are Valentıń (4058 m), the highest summit in the southern indicative of readvances or stillstands of the glacier prior to Andes. The Campos de Hielo del San Valentıń, a broad overall recession, have not been found to be as numerous icefield estimated to measure 1400 km2, straddles the and well-developed elsewhere on Taitao. At this location, cordillera at altitudes, according to Aniya and Enomoto the Laguna Elena glacier responded differentially to an (1986), between 1000 and 1500 m. Glaciers descending on apparently independent forcing regime. Various factors may the west side of the icefield, the San Rafael, San Quintıń, have played a role influencing the individualistic behavior and, less notably, the smaller Reicher and Gualas, terminate

Fig. 5. (top) Configuration of end moraines and outwash beyond Laguna Elena, Penıńsula de Taitao. Rıó Aldunate, draining the lake, follows the trend of the outer moraine belt, which is separated by outwash from the inner belt, located just beyond the lakeshore. The configuration, representing positions of the glacier assigned to early and late OIS 2, is repeated outside adjacent valleys that lie to the east, in the direction of Brazo Sur (USAAF 456.L.34). (bottom) Detail of multiple moraines and associated outwash deposited by the Laguna Elena glacier and a glacier flowing in the neighboring valley to the west (USAAF 456.V.34). 586 C.J. Heusser / Journal of South American Earth Sciences 15 (2002) 577–589

Fig. 6. Extent of the piedmont lobe of Glaciar San Rafael bounded by Te´mpanos I–II moraines at Laguna San Rafael. Istmo de Qfqui in the foreground is the location of Site 3. Glaciar San Rafael in 1944/45, descending from the Campos de Hielo del San Valentıń, crosses the Liquin˜e–Ofqui fault, its terminus calving in the tidal basin 2 km beyond the mountain front. Monte San Valentıń (4058 m) is center left on the skyline (USAAF 555.L.91). at or close to tide level. All are in a state of recession, having extremity of a piedmont lobe over an arc distance of last achieved maxima late in the nineteenth century AD approximately 35 km at the outer edge of the lake basin. (Lawrence and Lawrence, 1959; Winchester and Harrison, Te´mpanos III, which is made up of a remnant peninsula, 1996; Harrison and Winchester, 1998, 2000). small islands, and a submarine ridge extending from the The behavior and extent of Andean glaciers during the north shore, represents the location of the lobe as it last glacial maximum are almost completely unknown. It fluctuated within the lake during recession. At Istmo de may be assumed that valley glaciers advanced from the Ofqui (Fig. 2), the outermost Te´mpanos I moraine is 0.5 km Andes into the lowland, probably not unlike the glaciers on distant from the lakeshore and 10–15 m in height; the Penıńsula de Taitao and possibly moving along a Te´mpanos II immediately borders the lake at a height of consolidated terminus into the Golfo de Esteban and Golfo more than 5 m and rises to the southeast to 15 m. From de Penas. An alternative hypothesis is that Andean glaciers laminae deposited in a proglacial lake formed between the were less well nourished and, as a result, less active. Poor receded ice front and Te´mpanos I, Muller (1959a) estimated alimentation may have occurred, not only because storm an interval of 200–400 years and possibly much longer tracks were concentrated to the north, but also because the preceding emplacement of Te´mpanos II. 14 Andes lay in a precipitation shadow of the Taitao icecap. In A date of 3740 CyrBP for near-basal sediments in a one case, Muller (1959a) described an exposure of pre- small lake cored between the Te´mpanos I and II moraines at Te´mpanos Andean till of unknown age along Rıó de los Istmo de Ofqui (Site 3, Figs. 2 and 6) compares well with 14 Te´mpanos. Located beyond the Te´mpanos moraines of another of 3600 CyrBP, which postdates Te´mpanos I–II Laguna San Rafael, the till may relate to a set of older outwash deposited beyond the moraine along Rıó de los moraines (Fig. 2), the outermost of which is aligned with the Te´mpanos (Site 4, Fig. 2). These dates (Heusser, 1964) are 14 course of Rıó Dorotea, a tributary of Rıó de los Te´mpanos. the basis of an estimate of 4500–4000 CyrBP for 14 At Laguna San Rafael, Muller (1959a) recognized a Te´mpanos I–II. A date of 6850 CyrBP for a peat bed in threefold sequence of moraines resulting from the advances situ 11 km distant at far eastern side of Laguna San Rafael of Glaciar San Rafael. Te´mpanos I and II outline the (Site 5, Fig. 2) further implies that the Te´mpanos I–II C.J. Heusser / Journal of South American Earth Sciences 15 (2002) 577–589 587

Fig. 7. End moraines outline the piedmont lobe formed by the advance of the coalesced Gualas and Reicher glaciers in Golfo Elefantes. Cusps of a breached recessional moraine are visible at the entrance to the Gualas–Reicher valley (USAAF 555.L.85). moraines were built after early Holocene glacial recession. 1960) believes Te´mpanos I–II to be older and similar in According to Mercer (1982), the moraines date from the ﬁrst position to late Wisconsin moraines, an opinion shared by Neoglacial advance in the southern Andes; Te´mpanos III, Clapperton and Sugden (1988). Historical records, however, undated, is believed to represent the second Neoglacial show the glacier lobate at times and of near comparable size advance. in response to the periodic discharge of great volumes of ice Because of the imposing breadth of the Glaciar San from the Campos de Hielo del San Valentı´n down its steep, Rafael piedmont lobe and the massiveness of the Te´mpanos fault-crossed, western outlet. A map prepared by Simpson I–II moraines, a late Holocene setting for an advance of (1875) locates the terminus of the glacier in 1871 such magnitude has been questioned. Muller (1959a,b, approximately 8 km beyond the mountain front and 3 km

Fig. 8. Piedmont lobe of Glaciar San Quintıń inside the nineteenth century morainal loop in 1944/45. Earlier expansion of the lobe is represented by the moraine located beyond the course of Rıó San Tadeo. Laguna San Rafael is at the left (USAAF 456.R.175). 588 C.J. Heusser / Journal of South American Earth Sciences 15 (2002) 577–589 from the outermost moraines. Warren (1993) indicates Bennett, K.D., Haberle, S.G., Lumley, S.H., 2000. The last glacial- intermittent fluctuations that resulted in a cumulative Holocene transition in southern Chile. Science 290, 325–328. recession of 14 km since the late nineteenth century AD. Bird, J.B., 1938. Antiquity and migration of the early inhabitants of Patagonia. Geographical Review 28, 250–275. Thus, during widespread glacier activity in the southern Bru¨ggen, J., 1935. Informe geolo´gico sobre la regioń de Ofqui. Boletıń 14 Andes, estimated between 4500 and 4000 CyrBP Departamento de Minas y Petro´leo Ministerio de Fomento 52, 1–17. (Mercer, 1982), it is not inconceivable that accumulation Bru¨ggen, J., 1950. Fundamentos de la Geologıá de Chile, Instituto levels in the icefield were sufficiently high to produce the Geogra´fico Militar, Santiago, Chile. ´ Caldenius, C.C., 1932. Las glaciaciones cuaternarius en la Patagonia y piedmont lobes that gave rise to the Tempanos moraines. Tierra del Fuego. Geografiska Annaler 14, 1–164. The piedmont lobes of Glaciar San Rafael, the joint Clapperton, C.M., 1993. Quaternary Geology and Geomorphology of South Gualas–Reicher glaciers, and Glaciar San Quintıń, which America, Elsevier, Amsterdam. lie within the Tres Montes fracture zone and come from the Clapperton, C.M., Sugden, D.E., 1988. Holocene glacier fluctuations in same high-altitude icefield, apparently share a common South America and Antarctica. Quaternary Science Reviews 7, 185–198. history of fluctuations. Outermost moraines formed by the Clapperton, C.M., Sugden, D.E., Kaufman, D.S., McCulloch, R.D., 1995. combined Gualas–Reicher glaciers in Golfo Elefantes The last glaciation in central Magellan Strait, southernmost Chile. identify with Te´mpanos I and II; the moraine arched at Quaternary Research 44, 133–148. the mouth of the feeding valley is similar in position to Coronato, A.M.J., 1995. The late Pleistocene glaciation in tributary valleys Te´mpanos III (Figs. 2 and 7). Golfo Elefantes is 10 km of the Beagle Channel, Fuegian Andes, South America. Quaternary of South America and Antarctic Peninsula 9, 153–171. across and compares in size with the 11 km wide Laguna Denton, G.H., Heusser, C.J., Lowell, T.V., Moreno, P.I., Andersen, B.G., San Rafael. The lobe of Glaciar San Quintıń, advancing into Heusser, L.E., Schlu¨chter, C., Marchant, D., 1999a. Interhemispheric Golfo San Estaban, produced the only visible moraine linkage of paleoclimate during the last glaciation. Geografiska Annaler considered to be of Te´mpanos age, just outside Rıó San 81A, 107–153. Tadeo (Figs. 2 and 8). Earlier ice fronts of the glacier appear Denton, G.H., Lowell, T.V., Heusser, C.J., Schlu¨chter, C., Andersen, B.G., Heusser, L.E., Moreno, P.I., Marchant, D.R., 1999b. Geomorphology, to have calved into Golfo de Penas, an opinion expressed by stratigraphy, and radiocarbon chronology of Llanquihue drift in the area Bru¨ggen (1935, 1950). of the southern lake district, Seno Reloncavı´, and Isla Grande de Chiloe´, Tectonic activity in the Tres Montes fracture zone, in Chile. Geografiska Annaler 81A, 167–229. concert with climate, should be recognized as a contributing Forsythe, R.D., Nelson, E.P., 1985. Gelogical manifestations of ridge factor to the Te´mpanos advances. Tectonism is demon- collision: evidence from the Golfo de Penas–Taitao basin, southern Chile. Tectonics 4, 477–495. strable from the amount of thrusting along the Liquin˜e– Forsythe, R.D., Nelson, E.P., Carr, M.J., Kaeding, M.E., Herve, M., Ofqui fault as subduction of the Nazca plate beneath the Mpodozis, C., Soffia, J.M., Harambour, S., 1986. Pliocene near-trench South American plate took place. Consequent uplift of the magmatism in southern Chile: a possible manifestation of ridge Andes in the fracture zone accounts for the height of collision. Geology 14, 23–27. Grosse, J.A., 1990. Expediciones en la Patagonia Occidental, Editorial the cordillera and the presence of the Campos de Hielo del Andre´s Bello, Santiago, Chile. San Valentıń, as the icefield is nourished by the nearby Haberle, S.G., Lumley, S.H., 1998. Age and origin of tephras recorded in mainstream of the moisture-bearing southern Westerlies. postglacial lake sediments to the west of the southern Andes, 448Sto 478S. Journal of Volcanology and Geothermal Research 84, 239–256. Harrison, S., Winchester, V., 1998. 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