INTRODUCTION
The use of glacial sediments and landforms to reconstruct post-Wisconsinan alpine glacial histories is well established (e.g., Menounos et al., Reference Menounos, Osborn, Clague and Luckman2009). In the contiguous United States, the large stratovolcanoes of the Pacific Northwest are obvious places to study latest Pleistocene and Holocene glacier advances because of the relatively large volumes of glacier ice on the high peaks (Fig. 1). Indeed there has been much study of glacier activity on these volcanoes, but knowledge of the chronology of glacier advances is incomplete because dating has been based largely on end moraines, many of which were overridden during more extensive Little Ice Age (LIA) advances. Additionally, the timing of latest Pleistocene/Early Holocene advances and retreats remains contentious (e.g., Davis and Osborn, Reference Davis and Osborn1987; Thomas et al., Reference Thomas, Easterbrook and Clark2000; Kovanen and Beget, Reference Kovanen and Beget2005; Osborn et al., Reference Osborn, Menounos, Riedel, Clague, Koch, Clark, Scott and Davis2012). Kaufman et al. (Reference Kaufman, Porter, Gillespie, Gillespie, Porter and Atwater2003) reviewed Cascade glacier chronologies and concluded that, depending on the author and the mountain the author studied, Younger Dryas glaciers (1) advanced a little, (2) advanced a lot, or (3) were in a state of retreat. They concluded that these disparities should be resolved with additional research.
Figure 1. Map of Mount Rainier and surrounding area in Washington, U.S.A. Boxes with letters are study areas: a = Heine's (Reference Heine1998a, Reference Heineb) general study area; b = White River Park and Meadow X (see also Fig. 4); c = Crystal Lakes (see also Fig. 5); d = McNeeley type moraine location in Huckleberry Park (see also Fig. 2); e = Emmons Glacier and forefield (see also Fig. 7); f = Carbon Glacier and forefield (see also Fig. 8); g = South Tahoma Glacier and forefield (see also Fig. 9); h = Nisqually Glacier and forefield (see also Fig. 6). Key lakes discussed in this study are indicated and include Tipsoo, Henskin, and Upper Dewey lakes. Inset map shows the locations of notable volcanoes of the Cascade Volcanic Arc, including Mount Rainier (in red) and MM = Mount Meager, MC = Mount Cayley, MG = Mount Garibaldi, MB = Mount Baker, GP = Glacier Peak, MSH = Mount St. Helens, MA = Mount Adams, MH = Mount Hood, MJ = Mount Jefferson, TS = Three Sisters, NV = Newberry Volcano, CL = Crater Lake, MLV = Medicine Lake Volcano, SH = Mount Shasta, LP = Lassen Peak. Mount Stuart (MS) is a non-volcanic peak.
Figure 2. LIDAR image of the Huckleberry Park area. Dashed lines are moraine ridges. These features encompass the type McNeeley moraines first identified by Crandell (Reference Crandell1969). Solid black curved lines are the locations of Heine's (Reference Heine1998a, Reference Heineb) McNeeley I and II moraines in the drainage. Solid black dots indicate Heine's (Reference Heine1998a, Reference Heineb) coring locations.
Mount Rainier and other Cascade volcanoes offer the advantage of having tephra-bearing sediments that can serve as stratigraphic markers (Mullineaux, Reference Mullineaux1974; Sisson and Vallance, Reference Sisson and Vallance2009; Table 1). Rainier R tephra is a particularly useful marker for our study because it was deposited near the Holocene/Pleistocene boundary. Using R tephra along with dendrochronology, Crandell and Miller (Reference Crandell and Miller1974) argued that there was an early Neoglacial advance on Mount Rainier, preceding LIA advances. They also established that glaciers advanced prior to the deposition of R tephra, which at that time was dated to >8.75 ka (Crandell et al., Reference Crandell, Mullineaux, Miller and Rubin1962). In contrast, Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) radiocarbon-dated lake and bog cores near the heads of several valleys east of Mount Rainier and proposed two latest Pleistocene/Early Holocene advances on Mount Rainier—one shortly before the Younger Dryas and one afterwards.
Table 1. Select tephra layers found in Mount Rainier National Park that are referenced in this study.
a Ages are in calibrated years before 1950.
b Age estimated from the GISP2 ice core (Zdanowicz et al., Reference Zdanowicz, Zielinski and Germani1999).
Our study was initiated to test Heine's conclusions about pre-Neoglacial glacier activity on Mount Rainier and to resolve further the Neoglacial history. For the former goal, we employ high-resolution LIDAR and Google Earth imagery, field work, and a new lake sediment core. For the latter goal, we use lateral-moraine stratigraphy, which has been employed in the Canadian Cordillera for nearly four decades (e.g., Osborn, Reference Osborn1986; Ryder and Thomson, Reference Ryder and Thomson1986), but only recently in the United States (Osborn et al., Reference Osborn, Menounos, Riedel, Clague, Koch, Clark, Scott and Davis2012).
The definitions of Neoglacial/Neoglaciation and LIA vary between studies and regions. In this paper we take Neoglaciation to mean the climatic episode characterized by rebirth and/or growth of glaciers following maximum shrinkage during the Early Holocene warm interval (Porter and Denton, Reference Porter and Denton1967). It may encompass the last few to last several millennia, depending on the region. For the beginning of the LIA we use the definition of Clague et al. (Reference Clague, Menounos, Osborn, Luckman and Koch2009), about 1200 CE. The Younger Dryas cold interval, recorded as a period of glacier advance at the end of the Pleistocene, occurred between 12.9 and 11.7 ka before present, where present is 1950 CE (Davis et al., Reference Davis, Menounos and Osborn2009; Cheng et al., Reference Cheng, Zhang, Spotl and Edwards2020).
Setting
Mount Rainier (4392 m asl) is the highest mountain of the Cascade Range (Rogers, Reference Rogers1985) (Fig. 1). Several periods of andesitic to dacitic volcanism since 500 ka have built the current edifice of the volcano (Fiske et al., Reference Fiske, Hopson and Waters1963; Sisson and Lanphere, Reference Sisson, Lanphere and Pringle2008). Surficial deposits on Mount Rainier comprise Holocene debris flows and fluvial, glacial, and pyroclastic deposits (Crandell, Reference Crandell1969).
Twenty-eight named glaciers extend partway down the flanks of the mountain and have a total area of about 75 km2 as of 2021 (Beason et al., Reference Beason, Kenyon, Jost and Walker2022). Additionally, the volcano is spotted with dozens of unnamed permanent ice patches and snowfields (Beason et al., Reference Beason, Kenyon, Jost and Walker2022). The present retracted state of glaciers exposes extensive lateral-moraine complexes with proximal flanks sloping up to 60°, and to heights locally exceeding 100 m (Mills, Reference Mills1978). Currently, glaciers on Mount Rainier have negative mass balances and are in a general state of retreat (Riedel and Larrabee, Reference Riedel and Larrabee2011). The seven-year average (2003–2009) equilibrium-line-altitude (ELA) of Nisqually Glacier was approximately 3160 m asl, and that of Emmons Glacier was 2730 m asl (Riedel and Larrabee, Reference Riedel and Larrabee2011). In comparison, the average ELA estimated from several glaciers during the farthest extent of LIA advances is about 1965 m asl (Burbank, Reference Burbank1981, Reference Burbank1982).
Mount Rainier and the surrounding region experience a Pacific Maritime climate. Winters are typically mild and wet because of westerly low-pressure systems, and summers are warm and dry from northerly high-pressure systems (Brace and Peterson, Reference Brace and Peterson1998). Strong orographic effects influence precipitation and temperature gradients on the volcano. Northeasterly flow during winter storms enhances precipitation on the western and southwestern flanks of the volcano and reduces precipitation on the opposite sides. For example, weather stations on the south and southeast flanks of the mountain at Paradise (1647 m asl; 46.786°N, −121.742°W) and Longmire (825 m asl; 46.749°N, −121.812°W) record mean annual precipitation of 3200 mm and 2210 mm, respectively, whereas a weather station at Ohanapecosh (560 m asl; 46.731°N, −121.571°W) on the east flank of the volcano records mean annual precipitation of 1905 mm (National Park Service, 2021a). Average high and low January temperatures at Paradise, Longmire, and Ohanapecosh are 0.5°/−6°C, 2°/−4°C, and 4°/−1°C, respectively. Corresponding average July highs and lows are 18°/7°C, 24°/8°C, and 23°/9°C, respectively (National Park Service, 2021b).
Previous work
Apart from older studies of recent glacial recession by Russell (Reference Russell1898), Matthes (Reference Matthes1928), and Bender and Haines (Reference Bender and Haines1955), the first analysis of glacial history on Mt. Rainier was that of Sigafoos and Hendricks (Reference Sigafoos and Hendricks1961), who conducted a tree-ring study of the recent history of Nisqually Glacier. Later, Sigafoos and Hendricks (Reference Sigafoos and Hendricks1972) reported tree-ring ages for LIA moraines of eight glaciers on the mountain. Based on these studies, they reported evidence of advances terminating at about 1525, 1550, 1625–1660, 1715, 1730–1765, 1820–1860, 1875, and 1910 CE. These ages are from trees growing on moraines and thus are all minima.
The work of D.R. Crandell and U.S. Geological Survey colleagues on the glacial history of Mount Rainier, although now about 50 years old, still stands as the most comprehensive to date. Of particular relevance are a surficial geology map of Mount Rainier National Park (Crandell, Reference Crandell1969) and the Quaternary stratigraphy reported by Crandell and Miller (Reference Crandell and Miller1974). Crandell's map was published at a scale of 1:48,000 and was recently digitized by the National Park Service (2018). Crandell and Miller (Reference Crandell and Miller1974) assigned the glacier advances of the past several centuries (i.e., LIA) to the “Garda Stade”. Combining their own tree-ring work with tephra mapping and the tree-ring work of Sigafoos and Hendricks (Reference Sigafoos and Hendricks1961, Reference Sigafoos and Hendricks1972), they concluded that the two main periods of moraine building were 1730–1770 CE and 1830–1860 CE. Crandell and Miller (Reference Crandell and Miller1974) also documented other episodes of moraine building in the first half of the sixteenth century and the mid-seventeenth century. However, a few Garda moraines are mantled with tephra layer W, which was thought by Mullineaux (Reference Mullineaux1974) to be about 450 years old, suggesting that these moraines are older than 1500 CE (Table 1). In addition, the oldest Garda moraine of Carbon Glacier is older than trees that germinated before 1217 CE, which led Crandell and Miller (Reference Crandell and Miller1974) to suggest that the Garda Stade began prior to 1200 CE. Such a date might not be considered by some to be part of the LIA; definitions vary but Clague et al. (Reference Clague, Menounos, Osborn, Luckman and Koch2009) make a case that the LIA began about 1200 CE.
One or more pre-LIA advances on Mount Rainier are represented by moraines of similar form and extent to Garda moraines. They are overlain by tephra layer C and younger tephras, but not by tephra layer Y, and so are presumed to date between 4.4 and 2.2 ka (Table 1). Crandell and Miller (Reference Crandell and Miller1974) attributed these moraines to the “Burroughs Mountain Stade” and estimated an age for this stade between 3.0 and 2.5 ka. We found that moraines of this age are uncommon and infer that most were overridden or obscured by subsequent LIA advances. In this paper, we informally refer to a “Burroughs Mountain advance” for these rare Neoglacial moraines.
Crandell and Miller (Reference Crandell and Miller1974) also defined a latest-Pleistocene glacial episode, a small advance that they assigned to the “Sumas Stade” of Armstrong et al. (Reference Armstrong, Crandell and Easterbrook1965). They mapped deposits of this advance as “McNeeley Drift.” Although Crandell and Miller (Reference Crandell and Miller1974) never used the term “McNeeley advance,” the label was applied by subsequent authors and we adopt it here. McNeeley Drift consists of moraines overlain by R tephra (Table 1) that at the time Crandell and Miller published their report was thought to be >8.75 ka (Crandell et al., Reference Crandell, Mullineaux, Miller and Rubin1962). More recently, Samolczyk et al. (Reference Samolczyk, Vallance, Cubley, Osborn and Clark2016) assigned an age of about 10 ka to R tephra (Table 1); the age is discussed further and updated in this paper. McNeeley moraines are rare but where present, they typically lie up to a few hundred meters downvalley from Garda moraines. Many McNeeley deposits are moraines or relict rock glaciers within cirques or at cliff bases that show no evidence of LIA (Garda) activity; an example is the type McNeeley deposit 0.7 km south of McNeeley Peak (Fig. 2). This deposit, which appears to be, at least in part, a rock glacier complex, is discussed later in this paper. Crandell and Miller (Reference Crandell and Miller1974) suggested that the lack of McNeeley moraines in some of the glacial valleys may indicate that McNeeley moraines were less extensive than, and likely overrun by, subsequent Neoglacial advances in these locations. They considered McNeeley deposits to be a product of a late phase of the Fraser (Late Wisconsinan) Glaciation.
Burbank (Reference Burbank1981) dated LIA moraines on Mount Rainier using lichenometry, claiming it to be more reliable than dendrochronology. A linear extrapolation of a Rhizocarpon geographicum growth curve developed at Mount Rainier by Porter (Reference Porter1981) was considered “probably valid for 400 to 500 yr” (Burbank, Reference Burbank1981, p. 372), even though the oldest control point was only 140 years. Tree-ring counts were determined by Burbank (Reference Burbank1981, p. 373) “to provide minimum ages for forested moraines where lichen growth was inhibited.” Finally, Burbank (Reference Burbank1981) concluded that the presence of a tephra on a moraine provides a reliable minimum age for moraine construction, but the absence of a tephra that is known to be in the area may not provide a reliable maximum age. He concluded that Carbon, Winthrop, North Mowich, Cowlitz, and Ohanapecosh glaciers built moraines, respectively, in the early and middle sixteenth century; early, middle, and late seventeenth century; early, middle, and late eighteenth century; early, middle and late nineteenth century; and early twentieth century. Burbank (Reference Burbank1981) found tephra layer C (2.2 ka; Table 1) 8 m below the crest of a lateral moraine of Carbon Glacier dated using dendrochronology to older than 1217 CE by Crandell and Miller (Reference Crandell and Miller1974; Table 1). As a result, Burbank suggested that the till of most of the east lateral moraine of Carbon Glacier predates 2.2 ka and is probably an early Neoglacial deposit of Burroughs Mountain age.
Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) remapped McNeeley moraines in an area on the northeast flank of Mount Rainier that overlapped the study area of Crandell (Reference Crandell1969) and Crandell and Miller (Reference Crandell and Miller1974). He also radiocarbon-dated lake and bog sediments interpreted to be associated with the moraines. Heine (Reference Heine1998a) mapped two moraines in several cirques and concluded that there were two distinct late-glacial advances, which he named McNeeley I and II. There is only one site in Heine's and Crandell and Miller's overlapping study areas where McNeeley moraines were mapped at the same place. That site is just above Tipsoo Lake, where Heine and Crandell and Miller recorded a single moraine (Fig. 3). At Huckleberry Park, Crandell and Miller (Reference Crandell and Miller1974) and Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) mapped a single McNeeley moraine, but in different locations with different orientations (Fig. 2). Crandell and Miller (Reference Crandell and Miller1974) mapped no moraines at eight other sites where Heine (Reference Heine1998a, Reference Heineb) mapped double moraines.
Figure 3. LIDAR image of Tipsoo Lake and cirque showing coring site (asterisk) and the crest of the McNeeley moraine (dashed line), first mapped by Crandell (Reference Crandell1969) and supported by Heine (Reference Heine1998a, Reference Heineb). This moraine dams a small pond (Little Tipsoo Lake); outwash from the McNeeley glacier would have fed into Little Tipsoo Lake and Tipsoo Lake. Note that construction of the highway (SR 410) removed a significant portion of the moraine. LIDAR data: Mt. Rainier 2007 survey, WS DNR LIDAR Portal (2021).
Heine (Reference Heine1998a, Reference Heineb) reported a minimum age of ca. 13.2 ka (11.3 14C ka) for his earlier McNeeley I advance based on dates from cores taken from bogs or lakes dammed by the moraines at three sites—Upper Dewey Lake, Upper Henskin Lake, and White River Park (Fig. 1). Heine concluded that these minimum ages were close to actual ages and thus inferred that glaciers retreated from McNeeley I moraines shortly before ca. 13.2 ka, which led him to assign a pre-Younger Dryas age for his McNeeley I advance. Heine's (Reference Heine1997, Reference Heine1998a, Reference Heineb) McNeeley II moraines occur adjacent to, but slightly up-valley of, McNeeley I moraines, and thus were assumed to be younger. He inferred the moraines to be older than 8.75 ka based on (1) a local cover of R tephra, then thought to be that age (Crandell et al., Reference Crandell, Mullineaux, Miller and Rubin1962); and (2) a minimum age of 10.28–9.99 ka (9.14 ± 0.1 14C ka) from a sediment core collected from upper Dewey Lake (Heine, Reference Heine1998a, Reference Heineb). Heine further proposed that the McNeeley II advance occurred between 10.9 and 9.95 ka (9.80–8.95 14C ka) based on his interpretation that a layer with a lower content of organic matter than layers above and below it in cores from White River Park and Tipsoo Lake represents glaciogenic sediments from the McNeeley II advance upstream of the coring sites. Based on this assumed age range, Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) concluded that the McNeeley II advance post-dates the Younger Dryas event and, further, that there is no evidence of an advance during the Younger Dryas on Mount Rainier.
METHODS
Identification and mapping of pre-Neoglacial moraines
We used publicly available LIDAR data and high-resolution optical imagery available in Google Earth to identify and map moraines within the study area (Fig. 1; Supplementary Fig. 1). Bare earth LIDAR DEMs (2007–2008 survey) with a ground-sampling resolution of 1 m were downloaded from the Washington LIDAR Portal (lidarportal.dnr.wa.gov). These data were imported into ArcGIS to create hill-shade and slope-shade maps of the field area for detailed analysis. We used the LIDAR imagery to map prominent lateral and terminal latest-Pleistocene and Holocene moraines and associated periglacial deposits (e.g., protalus ramparts), evaluating the published mapping of Crandell (Reference Crandell1969), Crandell and Miller (Reference Crandell and Miller1974), and Heine (Reference Heine1998a, Reference Heineb).
In September 2021, we visited several sites of mapped McNeeley moraines to make observations and compare them to the available imagery. To compare our LIDAR and field-based mapping to that of Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) we geocoded the study map from his 1998b publication (Heine, Reference Heine1998b, fig. 1) using ground control points (GCPs) obtained from hill-shade LIDAR images. Using a Helmert transformation with cubic resampling, we calculated the RMS error of the 14 GCPs to be 3.09 pixels, or about ±15 m. The original map was resampled to 5 m and projected into UTM Zone 10 N (WGS84). We also compared our results to the georeferenced digitized surficial mapping of Crandell (Reference Crandell1969) and Crandell and Miller (Reference Crandell and Miller1974), both of which are available through the U.S. Geological Survey's National Geologic Map Database (U.S. Geological Survey, 2023), and draped the geolocated maps in Google Earth to aid in our assessment of the previous mapping.
Lake sediment coring
We collected a sediment core from Tipsoo Lake (Figs. 1 and 3) in 2010 to provide a continuous record of sedimentation from the surrounding catchment during terminal Pleistocene and Early Holocene time (Karlén, Reference Karlén1976, Reference Karlén1981). We used a modified Livingstone piston-coring device operated from a floating plywood platform following the techniques of Livingstone (1955) and Wright (Reference Wright1967). Tipsoo Lake is located ~19 km east of Mount Rainier's summit at an elevation of ~1480 m asl. The lake basin is downstream of an ice-free, west-northwest facing cirque with a floor that lies between 1700 and 1830 m asl (Heine, Reference Heine1997, Reference Heine1998a, Reference Heineb). Bathymetric data show that the lake has a maximum depth of approximately 2.5 m. A shallow pond named Little Tipsoo Lake is located just upstream of the south end of Tipsoo Lake and is dammed by a sediment ridge identified as a McNeeley moraine by Crandell (Reference Crandell1969) and later interpreted to be an Early Holocene McNeeley II moraine by Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) (Fig. 3). There is no evidence of Neoglacial glacier activity in the cirque above Tipsoo Lake.
Sediment core sections (total length 118 cm) were analyzed at the Lake Coring Lab in the Geology Department, Western Washington University. Cores initially were scanned for magnetic susceptibility (MS) at 2-cm intervals using the Bartington MS2C Core Logging Sensor. The core sections were then split in half, photographed, and described for visual stratigraphy. We conducted detailed analyses only on the deepest section of core, from 66 to 118 cm below the lake floor, because it had the greatest potential to contain a sedimentation record from the latest Pleistocene, Early Holocene, or both. For this section, we collected samples to analyze organic matter content and the grain size of the sediments. Organic matter (OM) content was assessed using loss-on-ignition (LOI) methods adapted from Cambardella et al. (Reference Cambardella, Gajda, Doran, Wienhold, Kettler, Lal, Kimble, Follett and Stewart2001) and Heiri et al. (Reference Heiri, Lotter and Lemcke2001). We collected samples at 1-cm increments, dried them at 100°C for 14–24 hours, and then placed them in a muffle furnace at 450°C for 4 hours. Grain size was measured by laser diffraction using a Malvern Mastersizer 2000 with autosampler. Prior to grain-size analysis, we treated each sample with hydrogen peroxide (H2O2; 30% solution) to remove organic sediment, and with sodium hydroxide (NaOH) to remove biogenic silica. Macrofossil and bulk organic samples were radiocarbon-dated to provide age control within the section (Table 2). Finally, we identified key tephra layers in the core based on their stratigraphic position and macroscopic characteristics. R tephra and Layer O samples were identified in the core and characterized using petrographic and geochemical techniques, as reported in Samolczyk (Reference Samolczyk2011) and Samolczyk et al. (Reference Samolczyk, Vallance, Cubley, Osborn and Clark2016).
Table 2. Sample site locations and reported radiocarbon ages from wood in lateral moraines and glacier forefields, and macrofossil and bulk organics in lacustrine sediments in Mount Rainier National Park.
1. AA = University of Arizona Accelerator Mass Spectrometry Lab; Keck = University of California Irvine W.M. Keck Carbon Cycle AMS facility; Beta = Beta Analytic Inc.; USGS = U.S. Geological Survey
2. Calibrations completed using Calib 8.2 (Stuiver et al., Reference Stuiver, Reimer and Reimer2021) and the IntCal20 Northern Hemisphere radiocarbon age calibration curve (Reimer et al., Reference Reimer, Austin, Bard, Bayliss, Blackwell, Bronk Ramsey and Butzin2020). Calibrated ages with a standard error >50 are rounded to the nearest decade; 2σ age ranges reported.
3. The outermost rings of each sample were collected when possible.
Lateral-moraine stratigraphy
Lateral moraines in many cases are composite landforms built by proximal-flank accretion or distal-flank accretion, and they consist of stacked or plastered tills of different ages deposited by multiple glacier advances (e.g., Humlum, Reference Humlum1978; Osborn, Reference Osborn1978; Röthlisberger and Schneebeli, Reference Röthlisberger, Schneebeli and Schlüchter1979; Matthews and Petch, Reference Matthews and Petch1982; Small, Reference Small1983; Osborn, Reference Osborn1986; Ryder and Thomson, Reference Ryder and Thomson1986; Iturrizaga, Reference Iturrizaga2008; Osborn et al., Reference Osborn, Menounos, Riedel, Clague, Koch, Clark, Scott and Davis2012). Unconformities between stacked/plastered tills may be marked by paleosurfaces containing non-glacial deposits or soils, representing periods when ice was not present. Organic matter and tephra associated with paleosurfaces can be dated to provide minimum and maximum ages for underlying and overlying tills, respectively. Detrital wood fragments not associated with a paleosurface and found lodged in lateral moraines provide maximum-limiting ages of encasing tills (Röthlisberger and Schneebeli, Reference Röthlisberger, Schneebeli and Schlüchter1979; Ryder and Thomson, Reference Ryder and Thomson1986; Osborn and Karlstrom, Reference Osborn and Karlstrom1989; Osborn et al., Reference Osborn, Robinson and Luckman2001).
The proximal flanks of the lateral moraines of Nisqually, Carbon, South Tahoma, and Emmons glaciers (Fig. 1) were inspected in the field for till packages demarcated by paleosurfaces. Samples of organic material associated with these surfaces, such as branches, roots, and stems of woody plants were collected for radiocarbon dating. To avoid inadvertently collecting modern wood, we only chose samples where the stratigraphic and exposure conditions precluded modern sources of wood and mass-wasting deposits. Wood samples were collected only if rooted (in situ) in a paleosurface buried by overlying tills, or well-lodged into till. Samples were air-dried, and the outermost rings were collected and sent for radiocarbon analysis.
Lahars and other debris flows occur frequently on the flanks of Mount Rainier, and their deposits are common in the low-lying glacial valleys surrounding the volcano (Crandell, Reference Crandell1971; Scott et al., Reference Scott, Vallance and Pringle1995; Walder and Driedger, Reference Walder and Driedger1995; Vallance et al., Reference Vallance, Cunico and Schilling2003). Lahar deposits emplaced onto lateral moraines can be incorrectly interpreted as till. Lahar deposits at Mount Rainier are typically massive or crudely stratified, poorly sorted, and may be graded (Scott et al., Reference Scott, Vallance and Pringle1995; Vallance, Reference Vallance and Sigurdsson2000). Deposits range in thickness from tens of centimeters to tens of meters, with thick deposits commonly occurring in valley bottoms and thinner veneers draping steep valley walls. Lahar deposits on Cascade volcanoes, unlike till, typically contain matrix vesicles, casts of wood fragments, or wood fragments themselves, and tend to be less heterolithologic than till; primary clasts are typically subangular to angular (Vallance, Reference Vallance and Sigurdsson2000). All sample sites in this study are in glacial valleys located in lahar inundation zones (Vallance et al., Reference Vallance, Cunico and Schilling2003). An attempt to distinguish between lahar and till deposits was made at each site, and any diamict having lahar characteristics was not considered a part of the glacier fluctuation record.
Radiocarbon age calibration and conventions
Samples were dated using radiocarbon methods at Beta Analytic Inc. (Miami, USA), the Accelerator Mass Spectrometry Lab at the University of Arizona (Tucson, USA), and at the W.M. Keck Carbon Cycle Accelerator Mass Spectrometer facility at the University of California Irvine (Irvine, USA) (Table 2). We calibrated radiocarbon ages using the IntCal20 Northern Hemisphere radiocarbon age calibration curve of Reimer et al. (Reference Reimer, Austin, Bard, Bayliss, Blackwell, Bronk Ramsey and Butzin2020) in Calib 8.2 (Stuiver et al., Reference Stuiver, Reimer and Reimer2021). Calibrated radiocarbon ages are reported as 2σ ranges and rounded to the nearest half decade if the reported error is larger than 50 years. Radiocarbon ages are presented as calendar ages (CE) when younger than 1 CE; older calibrated radiocarbon ages are presented as thousand years before present (ka), where “present” is considered to be 1950 CE.
RESULTS
Moraine record
Based on our mapping, two distinct groups of moraines exist in the study area. A third group, described by Crandell and Miller (Reference Crandell and Miller1974), is less definitive. The first group comprises sparsely vegetated, often sharp-crested, and poorly consolidated deposits close to contemporary glaciers. In most cases, the first group denotes glaciers that were 0.5–1.5 km more extensive than present-day glaciers (as of 2022). These features are products of the Little Ice Age or Garda Stade of Crandell and Miller (Reference Crandell and Miller1974), are hereafter referred to as ‘late Neoglacial moraines’, and are equivalent to those recognized in previous work (Sigafoos and Hendricks, Reference Sigafoos and Hendricks1972; Burbank, Reference Burbank1981).
The second distinct group of moraines, hereafter referred to as ‘McNeeley moraines’, as per Crandell and Miller (Reference Crandell and Miller1974), or more generally ‘pre-Neoglacial moraines’, are stable vegetated landforms that either occupy cirque basins in which no glaciers exist today or lie up to a few hundred meters beyond Neoglacial moraines. These landforms include classic cirque moraines as well as deposits that could be protalus ramparts or small rock glaciers (Crandell and Miller, Reference Crandell and Miller1974). Examples of these features include the McNeeley type deposit (Fig. 2) and the end moraine just upstream from Tipsoo Lake (Fig. 3). Some of these landforms have multiple crests.
The third, less-definitive moraine group comprises the ‘Burroughs Mountain moraines’ of Crandell and Miller (Reference Crandell and Miller1974), who provided four examples. The moraines are described as being older than Garda moraines because they are overlain by 2.2 ka tephra C, but younger than McNeeley moraines because they seem not covered by 4.4–3.6 ka tephra Y (Table 1). However, this interpretation is somewhat ambiguous because the absence of a tephra does not provide a definitive maximum age, and a moraine can be younger than an overlying tephra if the tephra has been reworked. Both points were acknowledged by Crandell and Miller (Reference Crandell and Miller1974).
Pre-Neoglacial moraines
Our mapping of McNeeley moraine crests using LIDAR data largely accords with the locations of McNeeley deposits identified by Crandell (Reference Crandell1969; Figs. 2 and 3). The much higher resolution of the bare-earth LIDAR data, however, allows a better definition of the extent and morphologies of the deposits. Also, we found more morainal deposits than Crandell (Reference Crandell1969). Comparison of our mapping and that of Crandell differs from that reported by Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb). Of the 17 McNeeley moraines identified by Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb), our analysis corroborates only a single deposit: the Tipsoo Lake moraine (Fig. 3). In most basins where Heine mapped McNeeley moraines, we find no evidence for such deposits. In a few cirques, Crandell (Reference Crandell1969) and our mapping show McNeeley deposits close to the headwalls, but not at locations mapped by Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb), which typically lie 0.5–1.0 km downvalley and 200 m lower than the deposits that we have mapped as McNeeley moraines. Below we provide a few examples of the differences in our and Heine's interpretations.
White River Park
The McNeeley moraines mapped by Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) in the vicinity of Sunrise Lake (Fig. 4) are low, rounded ridges adjacent to and below the meadows cored by Heine. These ridges all have a general orientation parallel to the valley axis, rather than across it. The taller ridges typically have bedrock cores, whereas the lower ridges are generally smoother and lack boulders. Exposures in the lower ridges from creek incision reveal sandy, tephra-rich sediment with scattered subangular clasts. These deposits are unlike glacial till so, combined with their orientation, we disagree with the interpretation that the landforms are terminal moraines impounding the meadows as mapped by Heine (Fig. 4). The only deposits that we interpret to be McNeeley age are the small protalus deposits that lie at the foot of cirque headwall slopes above and south of the meadows (Fig. 4).
Figure 4. LIDAR image of the White River Park and Meadow X areas. Dashed lines are McNeeley moraine ridges/rock-glacier deposits. Solid black curved lines show the locations of Heine's (Reference Heine1998a, Reference Heineb) McNeeley I (downvalley) and II (upvalley) moraines. Solid black dots indicate Heine's (Reference Heine1998a, Reference Heineb) coring locations. LIDAR data: Mt. Rainier 2007 survey, WS DNR LIDAR Portal (2021).
Meadow X
“Meadow X” lies immediately north of White River Park (Fig. 4). At this site, Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) described a pronounced moraine at the northeast end of the meadow. He interpreted this moraine to be McNeeley II in age and inferred that a less-distinct McNeeley I moraine occurred a short distance downvalley. Both LIDAR and field observations reveal no moraines in the vicinity of the meadow. Heine's McNeeley II moraine is a bedrock ridge and has no till exposures or erratics on the surface. As at White River Park, LIDAR imagery shows no evidence of cross-valley terminal-moraine loops or any lateral moraines upvalley in the vicinity of the meadow cored by Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb). Instead, the terrain appears to be dominated by bedrock-cored ridges that are dominantly oriented parallel to the valley axis. The only deposits that might be correlative to McNeeley deposits are small boulder-rich ridges at the foot of the valley headwall (Fig. 4).
Huckleberry Park
In Huckleberry basin near the McNeeley type locality of Crandell and Miller (Reference Crandell and Miller1974), Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) mapped a McNeeley II moraine just north and immediately downstream of a meadow that he cored (Fig. 2). The moraine mapped by Heine is downvalley of and oblique to the prominent sinuous ridge mapped by Crandell (Reference Crandell1969), Crandell and Miller (Reference Crandell and Miller1974), and us (Fig. 2). Our field observations at the site support observations made from the LIDAR imagery that there are no terminal or lateral moraines downstream of Heine's coring sites. Similar to the White River Park and Meadow X sites (Fig. 4), small hills and ridges downvalley from the meadow are longitudinally aligned with the valley axis and are cored by bedrock that crops out near their ridge lines. We observed no glacial deposits in Huckleberry Park other than those of Crandell and Miller's (Reference Crandell and Miller1974) type deposit.
Crystal Lakes
Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) mapped a McNeeley I moraine just downvalley of Lower Crystal Lake and a McNeeley II moraine in front of a small pond upvalley of the lake (Fig. 5). LIDAR imagery shows no moraines at these locations. We identified two older moraines that may be of McNeeley age (1) located upvalley of Upper Crystal Lake, and (2) originating from two cirques southwest of Upper Crystal Lake, between the upper and lower lakes.
Figure 5. LIDAR image of the Crystal Lakes area. Dashed lines are McNeeley moraine ridges/rock-glacier deposits as inferred in this study. Solid black curved lines show the locations of Heine's (Reference Heine1998a, Reference Heineb) McNeeley II moraine, between upper and lower Crystal Lakes, and McNeeley I moraine, downvalley of Lower Crystal Lake. Solid black dots indicate Heine's (Reference Heine1998a, Reference Heineb) coring locations. LIDAR data: Mt. Rainier 2007 survey, WS DNR LIDAR Portal (2021).
Neoglacial moraines
Fifteen radiocarbon ages from wood fragments collected from unconformities within till sequences exposed in the lateral moraines of Nisqually, Emmons, Carbon glaciers, and South Tahoma Glacier forefield (Fig. 1) constrain the ages of Neoglacial glacier advances on Mount Rainier (Table 2). These ages complement and expand the existing Neoglacial record based on tree rings, lichenometry, and tephrostratigraphy.
Nisqually Glacier
We collected wood samples from two sites on the east lateral moraine of Nisqually Glacier (Fig. 6). At site 1, located approximately 700 m upvalley from the Paradise–Longmire Road bridge, a stump (NIS09-10) in growth position protruding from till 11.6 m above the base of the moraine yielded an age of 1457–1622 CE. At site 2, ~700 m upvalley from site 1, a gully cut into the lateral moraine exposed three wood fragments approximately half-way up the proximal flank of the lateral moraine. A branch or stem (NIS09-03) protruding from the downvalley gully wall returned an age of 252–538 CE. A paleosurface, roughly 9 m below site 2 along the upvalley gully wall, is marked by wood-bearing coarse sand beds (<0.5 m thick) that extend parallel to the proximal moraine flank for approximately 20 m, indicating growth of the lateral moraine by accretion of a till sheet onto the proximal flank (proximal accretion); the sand beds separate the two till sheets. Two tree branches or stems (NIS09-03B and NIS09-03C) protruding from the sand beds along the paleosurface yielded ages of 258–404 CE and 261–409 CE.
Figure 6. Aerial imagery of Nisqually Glacier and forefield showing locations of dated wood samples collected from the east and west composite lateral moraines (see also Fig. 10). Imagery data: statewide NAIP 2015 True Color (NAIP: https://registry.opendata.aws/naip) [accessed May 2023].
A paleosurface in the west lateral moraine of Nisqually Glacier (Fig. 6), which ranges from 3 to 10 m below the moraine crest and is exposed over a distance of about 600 m, contained at least six protruding wood fragments lodged into tills, but not rooted. Two branches, NIS09-06A and NIS09-08A, located 10 m and 4 m below the moraine crest, respectively, returned ages of 1310–1630 CE and 1308–1402 CE.
Emmons Glacier
Multiple nested lateral moraines in the Emmons Glacier forefield are parallel to the valley axis. We collected samples at two sites on the innermost moraine crest about 500 m upvalley from where Sigafoos and Hendricks (Reference Sigafoos and Hendricks1972) dated moraine crests using dendrochronology (Fig. 7). At site 1, five wood fragments protruded from a paleosurface ~6 m below the moraine crest. The paleosurface was traced for ~135 m in a line parallel to the crest. One branch (EMM09-02) in this collection of wood samples yielded an age of 1476–1950 CE. At site 2, located 135 m upvalley from site 1, a protruding branch (EMM09-04) ~6 m below the moraine crest returned an age of 1478–1633 CE.
Figure 7. Aerial imagery of Emmons Glacier and forefield showing locations of dated wood collected from a west composite lateral moraine. Imagery data: statewide NAIP 2015 True Color (NAIP: https://registry.opendata.aws/naip) [accessed May 2023].
Carbon Glacier
We collected and dated wood from two sites on the west lateral moraine of Carbon Glacier (Fig. 8). A gully at site 1 exposed several pieces of wood in a layer ~9 m below the moraine crest. Two wood branches or stems (CA09-03 and CA09-04) yielded ages of 261–529 CE and 243–349 CE. A gully through the moraine at site 2, 60 m upvalley from site 1 and roughly at the same elevation, exposed several pieces of wood. A wood branch or stem (CA09-05) returned an age of 205–404 CE. Several wood fragments lodged in till were found at a level 7–11 m below the moraine crest in two gullies, delineating a paleosurface extending between sites 1 and 2.
Figure 8. Aerial imagery of Carbon Glacier and forefield showing the location of dated wood samples collected from the west composite lateral moraine. Imagery data: USA NAIP imagery: natural color (https://registry.opendata.aws/naip) [accessed May 2023].
South Tahoma Glacier
We collected wood samples from two sites where Tahoma Creek has incised into till in the forefield of South Tahoma Glacier, ~150 m upvalley from the Wonderland Trail bridge (Fig. 9). The two sites are located along the near-vertical, north gully wall above Tahoma Creek, ~150 m upvalley from nested LIA terminal moraines. These terminal moraines extend upvalley into heavily vegetated lateral moraines, which were dated to ca. 1550, 1835–1840, and 1860 CE by Sigafoos and Hendricks (Reference Sigafoos and Hendricks1972) using dendrochronological methods (Fig. 9).
Figure 9. Aerial imagery of South Tahoma Glacier forefield and Tahoma Creek channel showing the locations of collected wood samples (see also Fig. 10). The wood was exposed in a gully eroded by Tahoma Creek. The dashed lines indicate the mapped 1550, 1835–1840, and 1860 CE lateral-moraine crests (Sigafoos and Hendricks, Reference Sigafoos and Hendricks1972). Imagery data: USA NAIP imagery: natural color (https://registry.opendata.aws/naip) [accessed May 2023].
Figure 10. Images showing example stratigraphy at sample sites. (a) Image and line drawing show a gully incised into the proximal face of the east lateral-moraine crest of Nisqually Glacier (see also Fig. 6). Locations of the sandy seams along the paleosurface as well as radiocarbon-dated wood are shown in line drawing. Person for scale. (b) Image and line drawing show sediments exposed by incision on the north bank of Tahoma Creek in the forefield of South Tahoma Glacier (see also Fig. 9). Location of bedrock knob is outlined by a solid black line, and the dashed line indicates approximate upper elevation of the wood mat. Person for scale. (c) Image looking downstream. White arrow indicates the location of a large sheared stump (STAH09-01; 81 cm in diameter). Black arrows point to other wood fragments in the wood mat. Photographs by M. Samolczyk and K. Adams.
At site 1, a wood mat comprising sheared stumps in growth position, roots, and branches lies 12 m below the crest of the gully wall. The wood mat is covered by till and lies on a nearly vertical bedrock surface cropping out in the gully wall above Tahoma Creek (Fig. 10). The outer rings of two large sheared stumps (STAH09-01 and STAH10-01; 81 and 35 cm in diameter) in growth position and a branch or stem (STAH09-01A) yielded ages of 1509–1950, 1682–1939, and 1673–1942 CE, respectively. At site 2, ~30 m upvalley from site 1, a stem or branch (STAH09-02) protruding from till 15 m below the crest of the gully wall returned an age of 1663–1950 CE. The large calibrated age ranges of these three samples owes to the broad 2σ confidence interval in the radiocarbon calibration curve for samples that date to around 300 14C yr BP (Niklaus et al., Reference Niklaus, Bonani, Suter and Wölfli1994). We exclude the possibility that the wood mat is modern and is from vegetation that grew on the gully wall since the latest glacier advance, based on the complete absence of large trees growing on the steep gully walls of Tahoma Creek in the area where dated samples were collected and the concentration of wood in a layer below the thick (12–15 m) package of diamict. Several lahars have inundated the Tahoma Creek drainage during the Holocene (Walder and Driedger, Reference Walder and Driedger1994). However, the diamict covering the exposed wood does not contain sedimentological features that indicate deposition by a lahar (e.g., vesicles, gradation, and laminations). In addition, the sites are located in a zone of debris conveyance rather than deposition (Walder and Driedger, Reference Walder and Driedger1994); thus we conclude that the thick package of diamict (~12 m thick) overlying the wood mat is till.
Lacustrine record
The analyzed 52-cm-long section of the Tipsoo Lake core comprises three primary sedimentologic units, from top to bottom (Fig. 11): (1) silt-dominated tephra (layer O; 66–74 cm); (2) brown sandy silt with minor dark sand laminae (74–100 cm); and (3) purplish gray, well-sorted laminated clay (100–118 cm) containing internally bedded grayish brown tephra and lapilli (R tephra; 108.5–114 cm). Although not analyzed in detail, we note that sediments above 66 cm are visually equivalent to the brown sandy silt of unit 2 and are interlayered with tephra deposits.
Figure 11. Stratigraphy of Tipsoo Lake core. Photograph at the left shows simplified lithostratigraphy with the location of R tephra (108.5–114 cm) and position of radiocarbon-dated samples. Magnetic susceptibility indicates peaks at about 96 cm and 112 cm; the stratigraphically lower peak corresponds to R tephra, and the upper peak corresponds to a probable unidentified tephra. Organic content is highest in the brown sandy silt unit and lowest in the clay unit. Paraglacial sediments are shown by a decrease in grain size to clay between 100 and 118 cm depth, except for where R tephra occurs.
Maxima in magnetic susceptibility (MS) in the Tipsoo Lake core coincide with identified tephra layers O and R (Samolczyk, Reference Samolczyk2011; Samolczyk et al., Reference Samolczyk, Vallance, Cubley, Osborn and Clark2016) (Fig. 11). MS is relatively high in layer O (147.7 SI) and is consistently low (<30 SI) in the underlying brown sandy silt. A 1-cm-thick layer containing dark sand-sized grains at 95–96 cm depth, within the brown sandy silt, has relatively high magnetic susceptibility (147.7 SI; Fig. 11). The sand is most likely an unidentified tephra deposit rich in ferromagnetic minerals, similar to the unidentified deposits described by Mullineaux (Reference Mullineaux1974) and Hobson (Reference Hobson1976). MS rises again at 100 cm depth where the sediment first becomes clayey and is highest between 108.5–114 cm where R tephra is present, peaking at 112 cm (315.4 SI). MS drops sharply in clays underlying R tephra and reaches a value of 40 SI at the bottom of the core (118 cm depth).
Loss-on-ignition, a measure of organic-matter content, is consistently low (4%) in layer O, but abruptly increases in the brown sandy silt between 74 and 100 cm, with values ranging between about 8% to 28% (Fig. 11). The dark sand layer (95–96 cm), which is a probable tephra layer, has a low LOI value (5%). LOI decreases as the brown sandy silt grades into purplish gray clay at 100 cm, and remains consistently low to the bottom of the core at 118 cm (≤4%). LOI is lowest (<2%) in the R tephra horizon (108.5–114 cm).
Two tephra layers and three radiocarbon ages (one from a plant macrofossil and two from bulk sediment) provide age control for the Tipsoo Lake core (Table 2). Layer O, at 66–74 cm depth, is a conspicuous, exotic silicic tephra produced during the eruption of Mount Mazama at 7.777–7.477 ka (Zdanowicz et al., Reference Zdanowicz, Zielinski and Germani1999; Egan et al., Reference Egan, Staff and Blackford2015; Fig. 11; Table 1). R tephra, at 108.5–114 cm depth, is easily recognizable in stratigraphic sections because it is the only lapilli-bearing tephra deposit underlying layer O (Crandell and Miller, Reference Crandell and Miller1974; Heine, Reference Heine1998a; Samolczyk et al., Reference Samolczyk, Vallance, Cubley, Osborn and Clark2016; Fig. 11). R tephra has a modeled age of 10.13–9.96 ka (Samolczyk et al., Reference Samolczyk, Vallance, Cubley, Osborn and Clark2016), and new age constraints on R tephra, discussed later in this paper, from a sediment core taken from Tipsoo Lake suggest it could be as old as >11.6 ka. A pine needle collected at 88 cm depth, between tephra layers O and R, dates to 10.177–9.909 ka. Bulk sediment samples at 88 cm and 98 cm depth date to 11.069–10.588 ka and 12.62–12.191 ka, respectively (Table 2).
DISCUSSION
Latest Pleistocene/Early Holocene events
Moraine record
The extent, downvalley position, and groups of pre-Neoglacial moraines mapped by us broadly accord with the McNeeley deposits recognized and named by Crandell (Reference Crandell1969) and Crandell and Miller (Reference Crandell and Miller1974). In contrast, that mapping and our confirming re-evaluation differ from those of Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) who suggested (1) two distinct McNeeley advances, and (2) substantially greater downvalley extents of McNeeley glaciers. In all but two cases, we did not confirm the moraines mapped and described by Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb). In some catchments (e.g., White River Park, Crystal Lakes), we identified and mapped moraines possibly of McNeeley age, but they were many hundred meters upvalley from Heine's mapped extents. Given our doubt regarding Heine's (Reference Heine1997, Reference Heine1998a, Reference Heineb) mapping, we conclude that the ages he ascribed to McNeeley moraines provide little or no information regarding the glacial history of Mount Rainier. Our interpretation is that the McNeeley moraines as mapped by Crandell and Miller (Reference Crandell and Miller1974) and in this study are consistent with a single glacier advance older than R tephra.
Lacustrine and bog sediment record
Clastic-rich intervals of proglacial lake sediment with low organic matter (OM) content are a proxy record for glacial or paraglacial conditions in a catchment in which biological productivity is low and/or minerogenic input is high (e.g., Church and Ryder, Reference Church and Ryder1972; Karlén and Matthews, Reference Karlén and Matthews1992; Leonard and Reasoner, Reference Leonard and Reasoner1999; Matthews et al., Reference Matthews, Svein, Nesje, Berrisford and Andersson2000; Nesje et al., Reference Nesje, Matthews, Dahl, Berrisford and Andersson2001; Bilderback, Reference Bilderback2004; Menounos et al., Reference Menounos, Clague, Gilbert and Slaymaker2005; Osborn et al., Reference Osborn, Menounos, Clague, Koch and Vallis2007). Grain-size variations in proglacial lake sediments may reflect activity of warm-based glaciers, and several studies infer that organic-poor, clay- and silt-sized particles are indicators of active glaciation (e.g., Matthews et al., Reference Matthews, Svein, Nesje, Berrisford and Andersson2000; Nesje et al., Reference Nesje, Matthews, Dahl, Berrisford and Andersson2001; Bakke et al., Reference Bakke, Lie, Nesje, Svein, Dahl and Paasche2005; Bowerman and Clark, Reference Bowerman and Clark2011). However, factors affecting sedimentation, such as transport distance, sediment lithology, lake size, and sediment traps, also affect the characteristics and stratigraphy of proglacial sediments (Smith, Reference Smith1978; Matthews et al., Reference Matthews, Svein, Nesje, Berrisford and Andersson2000).
We interpret the brown sandy silt underlying layer O between 74 and 100 cm in the Tipsoo Lake core to be non-glacial in origin because of the high LOI and relatively low MS values (Fig. 11). At 100 cm depth, the organic-rich sandy silt grades into the underlying clay-rich sediments, referred to as “purplish gray clay” in Fig. 11. The clay continues to the base of the core at 118 cm, interrupted only by the R tephra at 108.5–114 cm. The clay is unique to depths 100–118 cm and is not observed elsewhere in the lacustrine sedimentation record (0–100 cm). The clay is well sorted and has a low LOI (≤4%) and higher MS values than the overlying brown sandy silt. The clay that is stratigraphically above and below R tephra has the same properties, thus we interpret that it is one unit from the same source that is interrupted by the deposition of R tephra. Because R tephra post-dates deposition of the McNeeley moraines and the clay is a single unit that pre- and post-dates the R tephra, the clay is assumed to be unrelated to glacier advance upstream. Therefore, the clay unit is likely associated with paraglacial conditions during or after the retreat phase of the McNeeley advance. Little Tipsoo Lake, located up-stream from Tipsoo Lake, may have acted as a sediment trap for any coarser grains during this period of sedimentation (Fig. 3).
Rainier R tephra at 108.5–114 cm provides an age constraint for paraglacial conditions in the cirque above Tipsoo Lake and for the McNeeley advance that built the upstream moraine (Figs. 11 and 13). The calibrated median age of 10.05 ka for Rainier R tephra reported in Samolczyk et al. (Reference Samolczyk, Vallance, Cubley, Osborn and Clark2016) was modeled from five bulk sediment or macrofossil ages from three locations on Mount Rainier (Heine, Reference Heine1997, Reference Heine1998a, Reference Heineb; Samolczyk et al., Reference Samolczyk, Vallance, Cubley, Osborn and Clark2016). Two new bulk sediment radiocarbon ages from our Tipsoo Lake core, one from 88-cm depth with a LOI value of ~18%, and one from 98 cm depth with a LOI value of ~28% and sitting just above the transition to clay at 100 cm depth, calibrate to median ages of 10.83 ka and 12.41 ka, respectively (Table 2). Sometimes bulk radiocarbon ages are erroneously older than macrofossil ages from the same stratigraphic horizon (e.g., Barnekow et al., Reference Barnekow, Possnert and Sandgren1998; Grimm and Nelson, Reference Grimm and Nelson2009; Wu et al., Reference Wu, Wang and Zhou2011). Indeed, in our Tipsoo Lake sediment core, the calibrated median bulk sediment age of 10.83 ka from 88 cm depth is about 780 years older than the calibrated median age of the macrofossil, 10.05 ka, from the same 88 cm depth. If that age offset is assumed to be about the same lower in the core, the calibrated median bulk sediment age of 12.41 ka at 98 cm depth can be corrected by subtracting 780 years, leading to an age of 11.6 ka for sediment at 98 cm depth. That would indicate R tephra is considerably older than the age of 10.05 ka previously published in Samolczyk et al. (Reference Samolczyk, Vallance, Cubley, Osborn and Clark2016).
The 98 cm depth bulk sample with the 11.6 ka age lies 10 cm above the top of R tephra in the Tipsoo Lake sediment core, with an unknown timespan of clay deposition between the two. We propose that age be considered as the new minimum-limiting age of R tephra, which suggests that the McNeeley moraines that were deposited before R tephra could have been formed during the Younger Dryas interval (Fig. 13).
Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) also recovered a sediment core from Tipsoo Lake, but his interpretation of those sediments differs from our own work. Heine did not identify R tephra in his core 13, leading him to interpret that Tipsoo Lake was not within the fallout area of R tephra. Our core contains R tephra, a visually distinct, coarse, pumiceous tephra layer, between 108.5 and 114 cm depth (Fig. 11; Samolczyk et al., Reference Samolczyk, Vallance, Cubley, Osborn and Clark2016), which suggests that the sediment record in Heine's core 13 is incomplete. An impenetrable horizon was encountered by Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb) at the base of his core (~78 cm sediment depth); although the basal sediments were not observed, they were interpreted as basal till from the McNeeley I advance (Jan Heine, personal communication, 2011).
The McNeeley advance
As described above, our inspection of LIDAR and Google Earth imagery, in conjunction with ground observations failed to confirm the double McNeeley moraines mapped by Heine (Reference Heine1997, Reference Heine1998a, Reference Heineb). We identified a single moraine above Tipsoo Lake, as did Heine (Fig. 3). Similarly, we agree that there is a well-defined McNeeley deposit near where Heine mapped a McNeeley II moraine in the Crystal Lakes basin, but his lower ‘McNeeley I’ moraine appears to be bedrock-cored hummocks, not a discrete terminal moraine (Fig. 5). We also found that Heine's McNeeley II moraine is mislocated: Heine mapped his moraine downvalley of a small pond in the drainage; LIDAR imagery demonstrates that the probable McNeeley deposit is immediately upvalley of the pond. The closest landform to a two-moraine McNeeley-age deposit in the study area may be Crandell and Miller's (Reference Crandell and Miller1974) type McNeeley deposit, which extends northward from Sourdough Ridge, southeast of McNeeley Peak (Fig. 2). This deposit is sourced from two adjacent cirques and is at least partly a relict rock glacier complex. The western part of the feature is stepped and conceivably could represent a minor re-advance after a first advance, but the eastern part has just one front. In any case, many rock glaciers have superposed lobes (e.g., Dusik et al., Reference Dusik, Leopold, Heckmann, Haas, Hilger, Morche, Neugirg and Becht2014) that may be dynamic rather than climatic in origin (e.g., Loewenherz et al., Reference Loewenherz, Lawrence and Weaver1989). Crandell (Reference Crandell1969) and Crandell and Miller (Reference Crandell and Miller1974) regarded the type McNeeley deposit to represent a single advance, and we see no compelling evidence to conclude otherwise.
The absence of sets of paired late-glacial cirque moraines in the area, combined with an interpretation of the lacustrine record from Tipsoo Lake, support Crandell and Miller's (Reference Crandell and Miller1974) original notion of a single McNeeley advance on Mount Rainier. The only age constraint on the advance remains the minimum age provided by R tephra, which we propose is >11.6 ka.
Cirque glacier expansion at Younger Dryas time in western Canada (Menounos et al., Reference Menounos, Goehring, Osborn, Margold, Ward, Bond and Clarke2017) and at Mount Baker (Osborn et al., Reference Osborn, Menounos, Riedel, Clague, Koch, Clark, Scott and Davis2012), which is close to Mount Rainier, suggests that the most parsimonious interpretation is a Younger Dryas timing for the McNeeley moraines (Fig. 13). However, we cannot be certain with the data at hand.
Early Neoglacial events
Given the sparse geomorphic evidence and dating challenges, we regard the ca. 4.4–2.2 ka Burroughs Mountain advance at Mount Rainier to be a tentative event (Fig. 13). Some of Crandell and Miller's (Reference Crandell and Miller1974) Burroughs Mountain moraines could be McNeeley or Garda in age, as they acknowledged. An early Neoglacial, LIA-scale advance of glaciers between about 3 and 2 ka would not be unexpected, since the Tiedemann and Peyto advances of similar age have been documented in the Coast and Rocky Mountains of western Canada (e.g., Ryder and Thompson, Reference Ryder and Thomson1986; Luckman et al., Reference Luckman, Holdsworth and Osborn1993; Menounos et al., Reference Menounos, Osborn, Clague and Luckman2009), but evidence of such an advance on Mount Rainier remains scant.
Later Neoglacial events
Dendrochronologic and lichenometric dates of end and lateral moraines from Sigafoos and Hendricks (Reference Sigafoos and Hendricks1972) and Burbank (Reference Burbank1981) provide minimum ages of moraine surface stabilization, but do not capture the composite nature of many lateral moraines revealed by moraine stratigraphy. Our ages from paleosurfaces in tills add to dendrochronologic studies at Nisqually, Carbon, Emmons, and South Tahoma glaciers by Sigafoos and Hendricks (Reference Sigafoos and Hendricks1972) and a lichenometric study at Carbon Glacier by Burbank (Reference Burbank1981).
Interpretations at individual glaciers
Nisqually Glacier plastered till over a vegetated surface on the proximal moraine flank of its east lateral moraine sometime between 252 and 538 CE (Figs. 6, 10, and 12). The west lateral moraine of Nisqually Glacier contains several pieces of wood that were buried when till was deposited on the proximal moraine flank between 1308 and 1630 CE. About 700 m downvalley, Nisqually Glacier advanced and overtopped its moraine crest between 1457 and 1622 CE, when it reached at least ~1.6 km downvalley of its current position. Sigafoos and Hendricks (Reference Sigafoos and Hendricks1972) dated an end moraine downvalley from our sample sites, with associated lateral moraines, and determined that the earliest LIA moraine stabilization occurred 1840 CE. Inner nested lateral moraines were also dated to 1857, 1870, and 1900 CE. The combined record indicates that Nisqually Glacier underwent Neoglacial advance starting as early as 250 CE and again as early as 1300 CE before eventually building the 1840 CE end moraine representing the maximum LIA advance. Nested lateral and recessional moraines from the nineteenth and twentieth centuries mark a period dominated by glacial retreat.
Figure 12. Distribution of radiocarbon ages of wood in lateral moraines and glacier forefields at Mount Rainier. Ages are calibrated with a standard error of 2 sigma. There are two clusters of ages, occurring in the first millennium and the second millennium CE, respectively. NIS = Nisqually Glacier, EMM = Emmons Glacier, STAH = South Tahoma Glacier, and CA = Carbon Glacier.
Carbon Glacier overtopped its west lateral moraine crest and buried a vegetated surface sometime between 205 and 529 CE (Figs. 8 and 12) during the first millennium CE. This record contrasts with the east-lateral record of Burbank (Reference Burbank1981) who observed tephra layer C (ca. 2.2 ka; Table 1) in tills below the moraine crest and interpreted that tills older than 2.2 ka, potentially from the Burroughs Mountain advance, lie directly below LIA tills. This implies that pre-LIA tills dating to the first millennium CE, like those found at our site on the west lateral moraine, are missing from the east lateral moraine or were not distinguished from LIA tills. The different preservation of evidence in the nested moraines of Carbon Glacier points to the complexity of resolving the glacier fluctuation record using moraine stratigraphy. Sigafoos and Hendricks (Reference Sigafoos and Hendricks1972) dated end and lateral moraines and determined that the oldest lateral-moraine set dates to 1500 CE with younger LIA nested moraine crests dating to 1835–1850 CE and 1875 CE. The combined record supports an advance of Carbon Glacier that is older than 2.2 ka as described by Burbank (Reference Burbank1981), as well as periods of moraine building in the first millennium CE that culminated during the LIA as early as the sixteenth century. The culminating advance was followed by a dominantly recessional phase in which nested lateral moraines dating to the nineteenth century were built.
Emmons Glacier forefield contains several sets of nested lateral moraines. Our examination of these moraines indicates the glacier overtopped a west lateral moraine as early as the late 1400s (Figs. 7 and 12). Sigafoos and Hendricks (Reference Sigafoos and Hendricks1972) dated lateral and end moraines downvalley from our study site and found that the oldest lateral-moraine crest dates to 1550 CE. This perhaps indicates that the late 1400s tills dated upvalley may be from the same advance that built the 1550 CE downvalley lateral moraine. Retreat from the end moraine that represents the maximum downvalley limit of Emmons Glacier was underway by the mid-1600s, and the glacier built several recessional end and lateral moraines during the eighteenth, nineteenth, and twentieth centuries (Sigafoos and Hendricks, Reference Sigafoos and Hendricks1972).
Wood fragments and sheared stumps in growth position are exposed in a wood mat on the north gully wall of Tahoma Creek, which has incised into the forefield of South Tahoma Glacier (Figs. 9, 10, and 12). Outer rings of a sheared stump (STAH10-01; 35 cm in diameter) in growth position date to between 1682 and 1939 CE and provide the tightest constraint on the age of the wood mat. The Tahoma Creek drainage is frequently inundated by lahars (Walder and Driedger, Reference Walder and Driedger1994, Reference Walder and Driedger1995), which have been known to ‘shear’ trees leaving behind stumps (J. Vallance, personal communication, 2010). But we attribute the shearing of the stumps, as large as 81 cm in diameter, in the wood mat to a glacier advance rather than a lahar.
The dated wood mat in the South Tahoma Glacier forefield is ~150 m upvalley from the oldest LIA end moraine and within the bounds of the lateral-moraine ridges that were dated dendrochronologically by Sigafoos and Hendricks (Reference Sigafoos and Hendricks1972). The end moraines and their lateral moraines date to 1550, 1835–1850, and 1860 CE (Sigafoos and Hendricks, Reference Sigafoos and Hendricks1972; Fig. 9). Our radiocarbon ages, together with the age of the end moraines (Sigafoos and Hendricks, Reference Sigafoos and Hendricks1972), suggest that South Tahoma Glacier retreated at least 150 m upvalley after building its maximum LIA end moraine in 1550 CE, allowing trees to establish in the forefield, prior to a glacier re-advance into the vegetated forefield that sheared the stumps found in growth position in our wood mat as early as the late 1600s CE and later constructed the 1860 CE moraines.
Regional comparisons
Our record of calibrated radiocarbon ages of wood in lateral moraines and previous records employing dendrochronology, lichenometry, and tephrochronology (Crandell, Reference Crandell1969; Sigafoos and Hendricks, Reference Sigafoos and Hendricks1972; Crandell and Miller, Reference Crandell and Miller1974; Burbank, Reference Burbank1981) indicate that there were two intervals of glacier expansion on Mount Rainier in the late Neoglacial period (Figs. 12 and 13). The earlier event, evident in the lateral-moraine record of Nisqually and Carbon glaciers, was an advance between ca. 200 and 550 CE. The time of this event aligns well with that of the First Millennium Advance (FMA; Reyes et al., Reference Reyes, Wiles, Smith, Barclay, Allen, Jackson and Larocque2006), which is documented in several areas of the western North American Cordillera (Menounos et al., Reference Menounos, Osborn, Clague and Luckman2009), perhaps in response to the climatic cooling termed the Late Antique Little Ice Age (Büntgen et al., Reference Büntgen, Myglan, Ljungqvist, McCormick, Di Cosmo, Sigl and Jungclaus2016). Evidence of this advance is not preserved in the end-moraine record on Mount Rainier; its end moraines were likely destroyed in more recent and extensive LIA advances of the last millennium. Our radiocarbon dating of the lateral-moraine stratigraphic record indicates that the LIA may have begun as early as ca. 1300 CE on Mount Rainier, aligning with the timing suggested in Clague et al. (Reference Clague, Menounos, Osborn, Luckman and Koch2009).
Figure 13. Schematic diagram of inferred glacier fluctuations on Mount Rainier over the past 14,000 years. A proposed timing of glacier advances is shown by curved black lines. Gray boxes show the Younger Dryas event and the Neoglacial period (Osborn et al., Reference Osborn, Menounos, Riedel, Clague, Koch, Clark, Scott and Davis2012). In the lake sediment record, the vertical black line inside the dashed rectangle indicates the position of the minimum-limiting age for R tephra (>11.6 ka) and the dashed rectangle shows a suggested period of paraglacial sedimentation, represented by clay sediments in the Tipsoo Lake sediment core, that post-dates the maximum extent of the McNeeley advance. In the lateral-moraine record, the black bars indicate the inferred timing on Mount Rainier of glacier advance during the First Millennium and Little Ice Age advances. BMA = Burroughs Mountain Advance; FMA = First Millennium Advance; LIA = Little Ice Age.
CONCLUSIONS
Our work on Mount Rainier indicates (1) that valley glaciers on high Cascade volcanoes such as Mount Rainier are substantial and their advances extended into forest. In such environments, lateral-moraine stratigraphy can augment end-moraine dating in establishing glacial history. However, lateral moraines do not provide the same information: end-moraine ages fix culminations of glacier advances, whereas ages from paleosurfaces in lateral moraines help define the progress of advances toward their culminations and may bracket the timing of culminations. (2) At least some of the lateral moraines on Mount Rainier are composite features, built up by successive glacial advances, with LIA till at the crest, a till dated to the first millennium CE below that, and still older till(s) below that. (3) Moraine stratigraphy establishes two major episodes of Neoglacial advance. The first is a pre-LIA advance on Mount Rainier that was less extensive than LIA maximum advances and was previously undocumented in the Cascade Range. It occurred between 200 and 550 CE and corresponds to the First Millennium Advance in western Canada. The second episode began around 1300 CE and culminated in the LIA maximum advances. (4) The early Neoglacial Burroughs Mountain advance proposed by Crandell and Miller (Reference Crandell and Miller1974) relies on ambiguous interpretations of tephra distribution. Although an early Neoglacial advance on Mt. Rainier is likely given records elsewhere in the Cordillera, evidence is scant at Mount Rainier. (5) A single episode of latest Pleistocene or Early Holocene ice advance on Mount Rainier is marked by the McNeeley moraines, as proposed by Crandell and Miller (Reference Crandell and Miller1974). Our mapping counters a previous interpretation of two such advances by Heine (Reference Heine1997, Reference Heine1998a). (6) Based on two additional radiocarbon ages from a sediment core from Tipsoo Lake, we revise the age estimate of R tephra to >11.6 ka, thereby making the McNeeley advance a possible consequence of the 12.9–11.7 ka Younger Dryas cold interval.
Supplementary Material
The supplementary material for this article can be found at https://doi.org/10.1017/qua.2023.63.
Acknowledgments
This research was supported by funding from the National Science and Engineering Research Council (NSERC) and the Canada Chairs Program, including NSERC Grant # 9026 to G. Osborn and M. Samolczyk. Funding was also provided by the University of Calgary and the Bentley University Faculty Research Awards. We are grateful for assistance provided by Joel Cubley, Jon Riedel, Eric Steig, Zoë Dietrich, Kristyn Adams, Randall Burke, Aline LaBrie, Josh Ouellet, Natalie Vogt, Jezra Beaulieu, Niki Clark, Nigel Davies, Dan Shugar, and Courtenay Brown. We would like to thank Brian Luckman, Greg Wiles, and James O'Connor for helpful reviews.
