Lake Moraine Research Articles

Hydrogeological implications of glacial landscape evolution at Skeiðarársandur, SE Iceland

Patterns of groundwater recharge and flow in present day and palaeo-glacial environments are governed by both geomorphology and subsurface sedimentology. This paper assesses the hydrogeological implications of glacial landscape evolution and develops a conceptual model of glacial landscape evolution and hydrogeological interaction. The ice-marginal zone of Skeiðarársandur, SE Iceland was selected as a case study of a temperate, actively-receding glacier landsystem that is affected by both surging behaviour and periodic glacier outburst floods (jökulhlaups). The groundwater table elevation was measured approximately every 2–5 days throughout two six-week summer field seasons in 2000 and 2001, and once in March 2001, using a network of shallow piezometers, and hydraulic conductivity was calculated based on grain-size distribution analysis of sampled aquifer materials. The hydraulic conductivity of the near surface aquifer at the study site spans three orders of magnitude and is highest and most varied in areas inundated by the November 1996 jökulhlaup. The shallow water table in the study area responds dynamically to precipitation events with the greatest fluctuation in an enclosed moraine lake basin with a perched aquifer underlain by ice and in a zone of outwash fans proximal to the ice margin. The seasonal decline in water table is greatest at the ice margin, reflecting the reduced winter recharge from the stagnant ice zone. Landsystems with morainic relief are associated with localised moraine/precipitation-fed groundwater systems. These localised groundwater systems are superimposed on the intermediate/regional scale groundwater systems that discharge further down sandur and offshore and are dominated by the gently-sloping geomorphologically-uniform outwash plain. Groundwater-fed lakes, formed in depressions from ice blocks deposited during jökulhlaups, may provide important ecological niches. The investigations at this site demonstrate that glacial outburst floods and glacier margin fluctuations produce a suite of sediments, landforms and environments that affect the hydrogeological system.

Simulating loss of primary silicate minerals from soil due to long-term weathering using Allogen: Comparison with soil chronosequence, lake sediment and river solute flux data

This paper presents ALLOGEN, a process model of soil mineral chemical weathering. Though designed principally to aid interpretation of lake sediment geochemical records by providing mass balance constraints for competing interpretations, the model is also applicable to more general questions about long-term weathering and soil development. The model is constructed around a generalised version of the mineral-weathering submodel of PROFILE, modified to minimise the need for site-specific data and to optimise performance for long-term change. Comparison with observed weathering rate data (river flux studies, chronosequences and lake sediment chemical stratigraphy) suggests that soil mineral depletion can be usefully simulated over timescales applicable to Quaternary and Holocene studies. To illustrate this, the plausibility of a weathering interpretation is demonstrated for sediment records at Lake Hope Simpson and Moraine Lake and the lake chronosequence at Glacier Bay. While long-term soil mineral depletion appears predictable, reliable simulation of past runoff quality is hampered by lack of a suitable long-term model for soil carbon.

Microbial community structure in moraine lakes and glacial meltwaters, Mount Everest

The bacterial diversity and abundance in two moraine lakes and two glacial meltwaters (5140, 5152, 5800 and 6350 m above sea level, respectively) in the remote Mount Everest region were examined through 16S rRNA gene clone library and flow cytometry approaches. In total, 247 clones were screened by RFLP and 60 16S rRNA gene sequences were obtained, belonging to the following groups: Proteobacteria (8% alpha subdivision, 21% beta subdivision, and 1% gamma subdivision), Cytophaga-Flavobacteria-Bacteroides (CFB) (54%), Actinobacteria (4%), Planctomycetes (2%), Verrucomicrobia (2%), Fibrobacteres (1%) and Eukaryotic chroloplast (3%), respectively. The high dominance of CFB distinguished the Mount Everest waters from other mountain lakes. The highest bacterial abundance and diversity occurred in the open moraine lake at 5152 m, and the lowest in the glacial meltwater at 6350 m. Low temperature at high altitude is considered to be critical for component dominancy. At the same altitude, nutrient availability plays a role in regulating population structure. Our results also show that the bacteria in Mount Everest may be derived from different sources.

On the rotifer fauna of Disko Island, Greenland, with notes on selected species from a stagnant freshwater lake

The rotifer fauna in Moraine Lake on Disko Island was investigated. 24 species were identified, of which 22 are new for Disko Island and three are new to Greenland. The new findings are presented in a species list that summarizes all records of rotifers from Disko Island, including several previously unpublished records. Furthermore, notes are given on the morphology of some selected species, including Eothinia elongata, Mikrocodides chlaena and Resticula nyssa.

Soils in a Geoecological Landscape Chronosequence on Glacial Drift in Southeastern Idaho

At the southwest corner of Yellowstone National Park, one geologist has mapped glacial moraines of three ages and later another mapped moraines of only two ages. Soils, including topographic differences, indicate glacial drift of four ages. These appear to be related to late Pinedale, early Pinedale, Bull Lake, and pre-Bull Lake drift that have been dated in northwestern Wyoming. The limits of late and early Pinedale moraines appear to correspond closely with ecological map unit boundaries and have specific soils that reflect greater weathering and soil development on early than on late Pinedale moraines. The weathering and soil development trend continues onto Bull Lake moraines, reaching a maximum there, with thick fine-loamy (or loamy-skeletal) argillic horizons. Soil development is no greater on the older pre-Bull Lake moraines, presumably because of development retardation by cryoturbation and mass wasting or solifluction. Ecological map units based on soil mapping do not correspond to limits of pre-Bull Lake (or Sacagewa) till mapped by a geologist. If geologists and pedologists had collaborated when mapping surficial geology and soils at the southwestern corner of the Park, both geology and soils (or ecological unit) maps and reports might be better representations of the landscapes.

Soils and Geomorphology in the Oregon Cascades: A Comparative Study of Illinoian-Aged and Wisconsin-Aged Moraines

Catena approaches to soil chronosequence studies in the Oregon Cascades are lacking in the literature. Here we compare pedogenesis with slope position on two different aged moraines. The younger Suttle Lake moraine (11 to 20 ka B.P.) contains a sequence of pyroclastic teprhas overlying glacial till and subsequently a series of buried soils. The older Jack Creek moraine (120 to 200 ka B.P.) is predominantly uniform in its parent material, glacial till. Both moraines show evidence of upslope erosion and down-slope deposition, being more active on the younger Suttle Lake moraine. Major differences in soil properties between the two moraines are associated with texture. Pyroclastic parent material is much coarser, with textures of sand and gravel, while older glacial till parent material typically displays a texture of loamy sand. Percent organic matter is higher in the finer glacial till. Harden's Profile Development Index values (i.e., PDI) were used to compare B-horizons of similar glacial till parent material. The PDI is of limited use in this study due to volcanism and glaciations producing alternating layers of parent material. However, B-horizons of similar parent material did obtain higher values on the older Jack Creek moraine. The index was also useful in identifying a much older buried B-horizon at the toeslope of the Suttle Lake moraine, possibly comparable to that of pre-Bull Lake-aged deposits in the Rocky Mountains. The use of soils as relative age indicators is cautioned for future work in the Oregon Cascades due to the complexity associated with an active volcanic landscape.

Map of the glacial geomorphology of north-central Québec-Labrador, Canada

Please click here to download the map associated with this article. The “map of the glacial geomorphology of North-Central Québec-Labrador, Canada”, based on aerial photograph interpretation, presents the distribution of glacial and glaciofluvial landforms, such as glacial lineations, eskers, ribbed moraine, and glacial lake shorelines. It covers an area of approximately 180,000 km2 between 53° and 56° 30′ N and 64° and 74° E and shows that north-central Québec-Labrador exhibits a more complex pattern of landforms than previously recognized. This mapping project was initiated as a test of the hypothesis that north-central Québec-Labrador exhibited cold-based conditions at least during the latest deglaciation as was suggested in previous studies based on glacial geomorphology. Cold-based conditions inhibit basal sliding and formation of subglacial landforms, which requires that marginal meltwater traces are the main source of information when reconstructing the spatial retreat pattern during a cold-based deglaciation. Therefore this new map also includes results of detailed mapping of the regional distribution of meltwater features.

Critical hydrologic conditions for overflow burst of moraine lake

Floodwater and debris flow caused by glacial lake burst is an important land process and a serious mountain disaster in glacial area of Xizang (Tibet) Autonomous Region, and the overflow burst is mainly caused by glacial landslide falling into moraine lake. On the premise that moraine lake is full, instantaneous burst in part of the lake bank happens, as flow velocity at burst mouth caused by overflow head is higher than threshold flow velocity of glacial till. Under some supposes, d(90) and d(10) of the glacial till in the hank were used as the threshold sizes of coarse and fine grains respectively. Thus, the formula of calculating threshold flow velocity of uniform sand was simplified, and threshold flow velocity of glacial till was calculated with the formula. Then, with synthesis formula calculating flow velocity of instantaneous part burst, flow velocity at overflow burst mouth was calculated, and calculation formula of critical height (H(0)) of overflow head was derived. Overflow head was caused by volume and surge of glacial landslide falling into moraine lake, calculation formulas of ascendant height (H(1)) of lake water surface and surge height (H(2)) on burst mouth caused by glacial landslide falling into moraine lake were derived. To sum up, critical hydrologic conditions of moraine lake burst with overflow form are: the burst is inevitable as H(1) > H(0); the burst is possible as H(1) H(0); the burst is impossible as (H(1)+H(2)) < H(0). In the factors influencing the burst critical conditions, it is advantageous for the burst that scale of the lake is 10(5)m(2) range; terminal glacial till is more fine and is even more uniform; the width of overflow mouth is even smaller than the length of the bank; the landslide has large scale and steep slip surface; and glacial end is close to the lake. With burst of Guangxiecuo Lake in Midui Valley of the Polongzangbu River in Xizang as an example, the burst critical conditions were tested.

Late Quaternary glaciation in the Northern Ogilvie Mountains: revised correlations and implications for the stratigraphic record

New geomorphic, paleolimnological, and radiocarbon data suggest that a terminal moraine complex in the Northern Ogilvie Mountains, Yukon Territory, Canada, may represent the McConnell Glaciation (Late Wisconsinan), rather than the Reid Glaciation (marine isotope Stage 8; Illinoian) as previously thought. Relict fluvial channels on the surface of the moraine and analysis of a suite of lake sediment cores from Chapman Lake, a closed-basin kettle on the surface of the moraine, suggest that flow from the Blackstone River passed over the moraine and through the lake until ca. 12 500 BP, at which time the Blackstone River was captured by the East Blackstone River, diverting flow from the lake. Subsequent incision by the Blackstone River has left its base level more than 10 m below the level of Chapman Lake. Perched former outlets from Chapman Lake indicate that this incision must postdate stream capture. Because the Chapman Lake moraine is a topographic barrier across the Blackstone River valley, incision must have occurred shortly after deposition of the moraine, suggesting that the landscape surrounding Chapman Lake is substantially younger than previously thought. Additional radiocarbon dates also suggest that kettle subsidence at Chapman Lake was ongoing during the early Holocene and that North Fork Pass moraine, 15 km upvalley from the Chapman Lake moraine, may have been formed during the Late Glacial rather than the McConnell Glaciation.

La Moraine du Lac Bluenose (Territoires du Nord-Ouest), une moraine à noyau de glace de glacier

Au sud du détroit du Dolphin et de l'Union, dans les Territoires du Nord-Ouest, des crêtes morainiques hautes de 100 m, composées de till à gros blocs marquent l'emplacement d'un front glaciaire à l'est et au nord du lac Bluenose. Les principales crêtes sont soit massives, soit composites avec de petites crêtes secondaires à leur sommet. En amont glaciaire (est) des crêtes, les formes de relief les plus fréquentes sont des collines recouvertes de blocs dont la hauteur atteint 60 m et des monticules entre lesquels se trouvent de nombreux lacs. Un important glissement de terrain au cœur de la moraine expose de la glace riche en sédiments, enfouie sous 3 m de till. Ce diamicton à matrice sabloneuse et riche en blocs exhibe une structure en colonnes et une fissilité prismatique. La glace enfouie qui incorpore des blocs et des cailloux est zonée, ce qui permet de déceler des plis et des déformations plus complexes. Le contact entre la glace enfouie et le diamicton est net, sub-horizontal et discordant. La glace est interprétée comme étant la partie basale d'un glacier enfouie par des sédiments glacigéniques, surtout du till. Dans une zone à écoulement à contre pente de la partie frontale de l'inlandsis du Wisconsinen supérieur des chevauchements ont transporté des sédiments qui ont recouvert la glace morte à la marge du front de glace active. Nous croyons que dans l'éventualité où un réchauffement climatique causerait la fonte de la glace enfouie, laquelle représente un volume important de la Moraine du Lac Bluenose, le relief serait transformé en un paysage bosselé semblable à celui qui existe dans des régions plus méridionales du Canada central.

TROPHIC STATE EVALUATION FOR SELECTED LAKES IN GRAND TETON NATIONAL PARK1

ABSTRACT: Increased visitation at Grand Teton National Park (GTNP) has raised concerns about impacts on surface water in the park. The purposes of this study are to perform a benchmark trophic state survey for comparison to future evaluations and to identify possible areas of concern. Four watershed regions based on geographic and geologic features were delineated for study. Six Alpine lakes, six Moraine lakes, three Valley lakes, and two Colter Bay lakes are evaluated. Lakes were sampled for total phosphorus (TP), chlorophyll‐a, and transparency. The water quality, as defined by trophic state, in the park is generally good. Oligotrophic to mesotrophic conditions were found in the Alpine and Moraine lakes and mesotrophic to eutrophic conditions were found in the Colter Bay and Valley lakes. High inflow TP concentrations in the park's northeast side may be due to the presence of natural geologic phosphate from the Phosphoria Formation.

Glaciation in the Great Basin of the Western United States

Forty individually named ranges, plateaus, and massifs draining wholly or partly into the Great Basin of the western United States show definite evidence of Pleistocene glaciation. The most obvious deposits are a family of moraines designated, among other names, “Tioga”, “Angel Lake”, and “Pinedale”. Such moraines generally can be traced from range to range away from described type moraines. These deposits have been numerically assigned to Late Wisconsinan glaciation in the Wasatch Range, White Mountains, Boulder Mountain, and Sierra Nevada on the basis of radiocarbon and surface-exposure ages, and have been assigned to Late Wisconsinan time in several other ranges on the basis of relative-age studies. The type Angel Lake moraine, and most other equivalent moraines across the Great Basin, are thick, hummocky, lobate piles of till rather than looping ridges. The thicknesses of the moraines (often 60+m) can be explained by heavy debris loads, and/or glacial advance, retreat, and readvance to the same positions a number of times, which is consistent with recent evidence that multiple Late Wisconsinan advances, possibly related to Heinrich and Dansgaard-Oeschger events, occurred in the Sierra Nevada. Pre-Angel Lake deposits occur in many Great Basin ranges, but it is currently difficult or perhaps impossible to determine if these deposits are equivalent to each other and what their relationship is to pre-Tioga deposits in the Sierra Nevada. Numerical ages are rare and relative-age studies suggest that pre-Angel Lake deposits may be products of more than one glaciation. Mapped pre-Angel Lake glaciers were longer than their Angel Lake counterparts, but the length differences do not translate into large differences in ELA depression. There is evidence of two minor latest Pleistocene or early Holocene advances in some ranges, judging from the presence of overlying Mazama tephra and/or weathering comparisons to local Angel Lake moraines. In the latter part of the Holocene, ELA's were sufficiently high that only the highest, wettest ranges developed Neoglacial glaciers. There does not appear to be a consistent pattern of latest Pleistocene/Holocene glacial fluctuations along an east–west transect through the Cordillera, or even through the Great Basin.

Late Pleistocene Glaciation of the Southwestern Ahklun Mountains, Alaska

Glacial deposits in the southwestern Ahklun Mountains, southwestern Alaska, record two major glacier advances during the late Pleistocene. The Arolik Lake and Klak Creek glaciations took place during the early and late Wisconsin, respectively. During the Arolik Lake glaciation, outlet glaciers emanated from an ice cap centered over the central portion of the Ahklun Mountains and expanded beyond the present coast. During the Klak Creek glaciation, ice-cap outlet glaciers terminated ∼60 km upvalley from Arolik Lake moraines. The area also supported numerous alpine glaciers that expanded from small massifs. During both episodes of glaciation, these alpine glaciers apparently reached their maximum positions sometime after the retreat of the ice-cap outlet glaciers. Equilibrium-line altitudes for reconstructed alpine glaciers of the Klak Creek glaciation average ∼390 ± 100 m elevation in the western Ahklun Mountains, which is at most 500 m, and possibly only 200 m, below the estimated modern equilibrium-line altitude. The maximum late Pleistocene advance in the southwestern Ahklun Mountains occurred during the early Wisconsin, similar to advances elsewhere in western Alaska, but in contrast to the isotopic signal in the deep-sea record of global ice volume. The restricted extent of Klak Creek glaciers might reflect the increased distance to the Bering Sea resulting from eustatic sea-level regression and decreased evaporation resulting from lower sea-surface temperatures and increased sea-ice extent.

Glacial Lake Outburst Floods in Upper Nainchu River Basin, Tibet

A large outburst flood from a glacial terminal moraine lake can cause severe damage to downstream communities. This paper presents a study on the outbursts of glacial terminal moraine lakes in the upper Nainchu River basin of Tibet. This study includes an investigation of the number, size, and distribution of glacial terminal moraine lakes; analysis of climatic and geographic factors that contribute to glacial lake outbursts; investigations of the outburst potential of the three largest lakes in the Nainchu River basin; simulations of floods that might occur from the glacial lakes; and a description of the monitoring and flood warning system setup.

Northwest outlet channels of Lake Agassiz, isostatic tilting and a migrating continental drainage divide, Saskatchewan, Canada

Lake cores obtained from the northwest outlet of glacial Lake Agassiz in northwest Saskatchewan, Canada, provide a minimum date for the cessation of the flood from the northwest outlet, and a chronology for abandonment of mid-Holocene channels that presently straddle the Mackenzie and Churchill drainage divide. The stratigraphy of a vibracore taken from Long Lake consists of a lower pebble gravel fining to massive sand, silty-clay and then fibrous peat. Wood fragments from the base of the clay yielded an accelerator mass spectrometry (AMS) date of 9120 BP. Because the lake is scour in origin and is in the head of the spillway, the date is considered to be a minimum estimate for cessation of the flood from the northwest outlet at the beginning of the Emerson Phase. A vibracore taken at Haas Lake in an abandoned channel surrounded by muskeg with no influent streams, consists of 0.8 m of stratified, pebble gravel containing abundant shell and wood fragments, overlain by 1.62 m of gyttja with a sharp, conformable lower contact. AMS dates range from 5590 BP from the topmost gravel to 3080 BP within the gyttja. The gravel is interpreted as fluvial, recording a river draining Wasekamio Lake north into the Clearwater River across the present-day drainage divide. Today, a drop of 2 m occurs from Wasekamio Lake southeast to Lac Ile-a-la-Crosse, along 150 km of lake basins parallel to the Cree Lake Moraine. The dates from Haas Lake suggest that before 5200 BP, the drainage divide was about 100 km further southeast, implying that during the Emerson Phase, lake level was controlled by a sill near Flatstone Lake at about 430 m instead of between Wasekamio Lake and the Clearwater River, as was previously proposed. Holocene differential isostatic uplift caused the flow reversal in the upper Churchill basin. Anastomosed channels at the mouth of rivers flowing north into lakes indicate that uplift is still active in the area today.

Soil translocation by water erosion from agricultural cropland into wet depressions (morainic kettle holes)

Wet depressions are important habitats in the agricultural landscape. In NE Germany, many of these depressions are morainic kettle holes containing temporary or permanent water bodies. Such kettle holes were formed at the end of the last glaciation, about 12,000 yr ago, by slowly melting blocks of buried dead ice. Because of the considerable relief in the resulting small inland catchments, sedimentation of eroded soil from croplands represents a major threat to these important habitats. In one of these small lakes, with a catchment area of 3.8 ha and a maximum slope of 17.6%, we determined the amount of erosion by running water, using soil sequences, sediment cores from the lake, and cesium analysis. The kettle hole itself contained about 3600 m3 of sediment, with a further 7700 m3 of colluvium around the depression: a total of 11,300 m3. In terms of slope steepness, only about 50% of the catchment area is prone to erosion by runoff. This means that during some 600 yr of agricultural land use, the mean soil loss from those 1.9 ha of erodible land amounted to about 0.6 m, i.e., 9000 t ha−1 or 15 t ha−1 yr−1. From the 14th century to 1960, the mean accumulation rate around the kettle hole was about 0.1 to 0.2 cm yr−1, increasing to 0.5 cm yr−1 after 1960 owing to intensified cultivation. Analysis of 137Cs activity indicates low erosion rates at the hilltops, increasing erosion at midslope and sedimentation around and within the kettle hole. This caused eutrophication and the slow filling-up of the small morainic lake. Two conservation strategies were considered feasible: either to create 10–20 m wide fringes of grassland around the kettle hole, combined with measures to control erosion in the croplands, or to stop agricultural activity within the catchment. In the study area, the latter option was implemented, based on contracts between the nature conservation authorities and local farmers. Water quality parameters are being monitored continuously to determine the impact of the conservation measures. After 3 yr of measurements, 12 parameters showed positive results.

Soil translocation by water erosion from agricultural cropland into wet depressions (morainic kettle holes)

Wet depressions are important habitats in the agricultural landscape. In NE Germany, many of these depressions are morainic kettle holes containing temporary or permanent water bodies. Such kettle holes were formed at the end of the last glaciation, about 12,000 yr ago, by slowly melting blocks of buried dead ice. Because of the considerable relief in the resulting small inland catchments, sedimentation of eroded soil from croplands represents a major threat to these important habitats. In one of these small lakes, with a catchment area of 3.8 ha and a maximum slope of 17.6%, we determined the amount of erosion by running water, using soil sequences, sediment cores from the lake, and cesium analysis. The kettle hole itself contained about 3600 m 3 of sediment, with a further 7700 m 3 of colluvium around the depression: a total of 11,300 m 3. In terms of slope steepness, only about 50% of the catchment area is prone to erosion by runoff. This means that during some 600 yr of agricultural land use, the mean soil loss from those 1.9 ha of erodible land amounted to about 0.6 m, i.e., 9000 t ha −1 or 15 t ha −1 yr −1. From the 14th century to 1960, the mean accumulation rate around the kettle hole was about 0.1 to 0.2 cm yr −1, increasing to 0.5 cm yr −1 after 1960 owing to intensified cultivation. Analysis of 137Cs activity indicates low erosion rates at the hilltops, increasing erosion at midslope and sedimentation around and within the kettle hole. This caused eutrophication and the slow filling-up of the small morainic lake. Two conservation strategies were considered feasible: either to create 10–20 m wide fringes of grassland around the kettle hole, combined with measures to control erosion in the croplands, or to stop agricultural activity within the catchment. In the study area, the latter option was implemented, based on contracts between the nature conservation authorities and local farmers. Water quality parameters are being monitored continuously to determine the impact of the conservation measures. After 3 yr of measurements, 12 parameters showed positive results.

Cosmogenic 36Cl and 10Be ages of Quaternary glacial and fluvial deposits of the Wind River Range, Wyoming

We measured cosmogenic 36 Cl in 56 samples from boulders on moraines and fluvial terraces in the vicinity of the Wind River Range, Wyoming. We also measured 10 Be in 10 of the same samples. Most of the 10 Be ages were in good agreement with the 36 Cl ages, indicating that rock-surface erosion rates were very low. The oldest moraine investigated, the type Sacagewea Ridge site, yielded only a limiting minimum age of >232 ka. The oldest moraines in the type Bull Lake complex also could be constrained only to >130 ka. The main sequence of type Bull Lake moraines yielded age distributions indicating deposition within the intervals 130 to 100 ka and 120 to 100 ka; the best estimates are closer to the upper limits of these ranges, and associated uncertainties are in the range of 10% to 15%. These uncertainties could permit deposition in either marine isotope stage 6 or stage 5d. We found no evidence of glacial deposits dating to marine isotope stage 4. Both Bull Lake–age moraines from Fremont Lake, on the opposite side of the Wind River Range, and boulders on a fluvial terrace above the Wind River, gave age distributions very similar to that of the second oldest Bull Lake advance (ca. 130 to 100 ka). The distribution of boulder ages for Pinedale moraines at Bull Lake indicated deposition between 23 and 16 ka, nearly identical to the distribution of 10 Be ages previously reported for the type Pinedale moraines at Fremont Lake.

Latest pleistocene and early Holocene fluctuations of glaciers in the Canadian and northern American Rockies

In the Canadian and northern American Rockies small-scale fluctuations of glaciers during and after late Wisconsinan deglaciation have been identified using stratigraphy of superimposed glacial deposits, geomorphology, and records of glacial advance in lake and peat sediments. Several authors have proposed that valley-glacier readvances of relatively modest scale followed the late Wisconsinan maximum. Evidence for some of these is difficult to evaluate from the literature and no deposits recording such readvances have been numerically dated. Several minimum-limiting radiocarbon dates for deglaciation suggest ice had retreated to within a few tens of km of present limits by ca. 12 ka BP, and to very near present limits by ca. 11 ka BP. One or more minor glacial advances, or stillstands during recession, evidently occurred in valley heads prior to 11 ka BP. Part of the evidence consists of moraines a few km downvalley from subsequently emplaced Little Ice Age and Crowfoot moraines. The Piper Lake moraine in the Mission Mountains of Montana is overlain by Glacier Peak G tephra, and thus has a minimum age of 11,200 14C years BP. The Crowfoot Advance, a minor advance of about the same magnitude as Little Ice Age advances, occurred between ca. 11,300 and 10,000 14C years BP and is thought to be related to the Younger Dryas climatic reversal. Crowfoot moraines have been found from Jasper National Park on the north to the Mission Mountains on the south. Crowfoot ELAs were an average of 40 m lower than modern ELAs around the Canada-U.S. border. There have been past proposals of significant early Holocene glacial advances in the Rockies, i.e. after Crowfoot time but before the LIA, but recent evidence indicates that glaciers then were less extensive than at present.

Late Quaternary Vegetation and Climate of the Wind River Range, Wyoming

Sediments from Rapid Lake document glacial and vegetation history in the Temple Lake valley of the Wind River Range, Wyoming over the past 11,000 to 12,000 yr. Radiocarbon age determinations on basal detrital organic matter from Rapid Lake (11,770 ± 710 yr B.P.) and Temple Lake (11,400 ± 630 yr B.P.) bracket the age of the Temple Lake moraine, suggesting that the moraine formed in the late Pleistocene. This terminal Pleistocene readvance may be represented at lower elevations by the expansion of forest into intermontane basins 12,000 to 10,000 yr B.P. Vegetation in the Wind River Range responded to changing environmental conditions at the end of the Pleistocene. Following deglaciation, alpine tundra in the Temple Lake valley was replaced by a Pinus albicaulis parkland by about 11,300 14C yr B.P. Picea and Abies, established by 10,600 14C yr B.P., grew with Pinus albicaulis in a mixed conifer forest at and up to 100 m above Rapid Lake for most of the Holocene. Middle Holocene summer temperatures were about 1.5°C warmer than today. By about 5400 14C yr B.P. Pinus albicaulis and Abies became less prominent at upper treeline because of decreased winter snowpack and higher maximum summer temperatures. The position of the modern treeline was established by 3000 14 C yr B.P. when Picea retreated downslope in response to Neoglacial cooling.