Little Ice Age Glacial Activity in Strathcona Provincial Park, Vancouver Island, British Columbia, Canada

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Little Ice Age glacial activity in Strathcona Provincial Park, Vancouver Island, British Columbia, Canada

Dave H. Lewis and Dan J. Smith

Abstract: Dendroglaciological and lichenometric techniques are used to establish the Little Ice Age (LIA) history of two glaciers (Colonel Foster and Septimus) in Strathcona Provincial Park, Vancouver Island, British Columbia. Our lichenometric investigations were preceded by the development of a locally calibrated Rhizocarpon geographicum growth curve (1708–1998 A.D.). Documentation of a 3–4-year ecesis interval for both trees and lichen greatly reduces one of the main uncertainties in using geobotanical methods for dating LIA landforms. The moraine dates provided, therefore, give a good approximation of the shift in climate conditions that lead to the retreat of the glaciers and subsequent moraine stabilization. Geobotanical evidence records three synchronous episodes of LIA moraine deposition at both glaciers: two prominent moraines at each site are dated to the early 1700s and late 1800s, with a third, smaller moraine dated to the mid 1930s. Moraines deposited prior to 1397 A.D. were also recorded at Colonel Foster Glacier; however, precise dating of these moraines was not possible. The moraine records from Strathcona Provincial Park suggest two possible modes of glacier response: (i) synchronous responses to larger-scale climatic forcing, and (ii) asynchronous responses to local factors such as microclimate, topography, and glacier geometry. The Vancouver Island LIA record was evaluated in the context of LIA results from the Pacific North American (PNA) Cordillera. It compares well with regional moraine records from coastal British Columbia, Washington, Alaska, and the Canadian Rocky Mountains, suggesting a regional response of PNA glaciers to climate change associated with the LIA. Résumé : Des techniques dendroglaciologiques et lichénométriques sont utilisées pour établir l’historique du Petit Âge Glaciaire de deux glaciers (Colonel Foster et Septimus) dans le parc provincial Strathcona, sur l’île de Vancouver, Colombie-Britannique. Nos études lichénométriques ont été effectuées après le développement d’une courbe de croissance de Rhizocarpon geographicum (1708 à 1998) calibrée localement. La documentation d’un intervalle écésis de 3–4 ans, à la fois pour les arbres et pour les lichens, réduit grandement les principales incertitudes quant à l’utilisation de méthodes géobotaniques pour dater les formes de relief du Petit Âge Glaciaire. Les dates de la moraine fournissent donc une bonne approximation du décalage des conditions climatiques qui a conduit au retrait des glaciers et à la stabilisation subséquente des moraines. Les évidences géobotaniques documentent trois épisodes synchrones de déposition de moraine du Petit Âge Glaciaire aux deux glaciers : deux moraines proéminentes à chaque site ont été datées du début des années 1700 et de la fin des années 1800; une troisième moraine, plus petite, date du milieu des années 1930. Des moraines déposées avant 1397 sont aussi enregistrées au glacier Colonel Foster; toutefois, il n’a pas été possible de dater ces moraines avec précision. Les évidences contenues dans les moraines du parc provincial Strathcona suggèrent deux modes possibles de réponse des glaciers : (i) des réponses synchrones au forçage climatique de grande échelle et (ii) des réponses asynchrones à des facteurs locaux tels que le microclimat, la topographie et la géométrie des glaciers. Les évidences du Petit Âge Glaciaire sur l’île de Vancouver ont été évaluées dans le contexte des résultats du Petit Âge Glaciaire de la cordillère Pacifique-Amérique du Nord. Ces évidences se comparent bien aux évidences contenues dans les moraines régionales de la côte de la Colombie-Britannique, de Washington, de l’Alaska et des Rocheuses canadiennes, suggérant que les glaciers de la cordillère Pacifique-Amérique du Nord aient réagi aux changements climatiques associés au Petit Âge Glaciaire. [Traduit par la Rédaction] Lewis and Smith 297

Received 30 April 2003. Accepted 3 November 2003. Published on the NRC Research Press Web site at http://cjes.nrc.ca on 10 March 2004. Paper handled by Associate Editor J.R. Desloges. D.H. Lewis and D.J. Smith.1 University of Victoria Tree-Ring Laboratory, Department of Geography, University of Victoria, Victoria, BC V8W 3P5, Canada. 1Corresponding author (e-mail: [email protected]).

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Introduction mountain ranges along Pacific North America provide a comparative perspective on LIA glacier activity in Alaska, British Many glacier forefields in the southern Canadian Cordillera Columbia and Washington State (Lewis 2001; Larocque and contain freshly deposited moraines (Luckman 1993; Smith Smith 2003) (Fig. 2). A summary of these findings suggests et al. 1995). Recent surveys attribute many of these moraines that there were at least seven distinct moraine-building episodes to glacial advances instigated by mass balance changes that within the last 800 years. Broadly synchronous early-LIA accompanied the Little Ice Age (LIA) climatic episode (Burbank events are dated to the 12th, 13th, and 14th centuries, with 1981, 1982; Porter 1981; Ryder and Thomson 1986; Ryder mid- to late-LIA events recorded in the early 16th, early 1987; Desloges and Ryder 1990; Wiles and Calkin 1990; 17th, early 18th, and late 19th centuries (Fig. 2). Clague and Mathewes 1996; Smith and Laroque 1996; Wiles The correspondence between these moraine records sug- et al. 1999; Smith and Desloges 2000). Although there are gests that glaciers in Pacific North America likely responded many well-constrained LIA glacial records describing these in a similar fashion to climate-induced mass balance fluctuations advances from the Canadian Rocky Mountains (Luckman throughout the LIA. This finding corroborates that of recent 1993; Smith et al. 1995; Luckman 2000), comparatively little glacier–climate studies in the region that highlight congruent research has been undertaken in the southern British Columbia mass balance behaviour at glaciers that are up to 500 km Coast Mountains (i.e., Mathews 1951; Ryder and Thomson apart (Letréguilly 1988; Letréguilly and Reynaud 1989, 1990). 1986; Smith and Desloges 2000; Larocque and Smith 2003). These relationships confirm the likely role regional circulation Within southern British Columbia, the marked retreat of most patterns played in modulating the behaviour of glaciers in contemporary ice fronts from their maximum LIA positions Pacific North America throughout the LIA (Yarnal 1984; (Smith and Desloges 2000; Larocque and Smith 2003) indicates Walters and Meier 1989; McCabe and Fountain 1995; Moore that, as a group, these glaciers are sensitive to historical climate 1996; Hodge et al. 1998; Bitz and Battisti 1999; McCabe et trends (Letréguilly and Reynaud 1989; Walters and Meier al. 2000; Moore and Demuth 2001). 1989; Brugman 1992; McCabe and Fountain 1995; Bitz and Battisti 1999; Lewis 2001). Study sites The intention of our research was to describe the LIA glacial activity of cirque glaciers located on Vancouver Island, British Field research was conducted in the forefields of two cirque Columbia (Fig. 1). While prior research had established that glaciers, Colonel Foster and Septimus, located in Strathcona this isolated grouping of glaciers was sensitive to 20th century Provincial Park (Strathcona PP) on central Vancouver Island, climate change (Ommaney 1972), insights into their LIA British Columbia, Canada (49°40′N, 125°40′W) (Fig. 1). behaviour is restricted to the findings of Smith and Laroque Strathcona PP straddles the Vancouver Island Ranges and (1996) at Moving Glacier (Fig. 1). Dendroglaciological results contains the highest summits (2228–2134 m asl) on Vancouver show that Moving Glacier advanced close to its maximum Island. While glaciers are not uncommon in the park, most LIA position by 1718 A.D. and that, following this period of are relatively small (Ommaney 1972), and many have lost expansion, the glacier experienced only minimal retreat before over 80% of their LIA surface area within the last century the first aerial photograph was taken in 1931. (Table 1). In this paper, we present the LIA glacial histories of Colonel Tree-line climates in Strathcona PP are typically cool and Foster and Septimus glaciers (unofficial names) located in wet, with deep late-melting snowpacks persisting into July Strathcona Provincial Park on Vancouver Island (Fig. 1). We and August (Egan 1997). Mean annual temperatures at tree-line chose to focus our investigations at these two sites following average 3.0 °C, with the coldest month averaging –5.1 °C an examination of historical aerial photographs showing the and the warmest month 11.1 °C (Klinka et al. 1991; Klinka 212 glaciers and snowpacks inventoried by Ommaney (1972). and Chourmouzis 2000). Annual precipitation totals reach Partially forested and nested terminal and lateral moraine up to 5000 mm/year, with late-season snowpack depths at complexes at Colonel Foster and Septimus glaciers allowed times exceeding 900 cm (Egan 1997; B.C. River Forecast for the application of dendroglaciologic and lichenometric Centre 2000). techniques to describe their LIA history. The results of these The vegetation above 900 m asl is almost entirely within investigations add to our knowledge of the historical behaviour the Mountain Hemlock (MH) Zone (Kojima and Krajina of glaciers on Vancouver Island, and are used to place their 1975; Klinka and Chourmouzis 2000). The MH Zone in LIA activity in the context of the similar records from Pacific Strathcona PP is characterized by open stands of old-growth North America. mountain hemlock (Tsuga mertensiana [Bong.] Carr.), yellow- cedar (Chamaecyparis nootkatensis [D. Donn.] Spach.), and Little Ice Age in Pacific North America amabilis fir (Abies amabilis [Dougl.] Forbes) trees (Hnytka The term “Little Ice Age” was initially used to describe an 1990). A discontinuous forest cover and a mosaic of tree extended cool period of renewed but moderate glaciation follow- islands characterize the upper limits of the Mountain Hemlock ing the climatic optimum of the early Holocene (Matthes Parkland subzone (Egan 1997; Klinka and Chourmouzis 2000). 1939). More recently, LIA has been used to describe two conjoining periods of glacier activity (Grove 1988, 2001): an Colonel Foster Glacier “early-LIA” episode between -1100 and 1300 A.D. and a Colonel Foster Glacier is located in a northeast-facing “late-LIA” interval, when glaciers expanded and fluctuated cirque at the base of a steep headwall below the summit of around more advanced positions, from -1700 A.D. to the Mount Colonel Foster in northern Strathcona Park (49°46′N, early 1900s (Luckman and Villalba 2001). 125°51′W; Fig. 2). The glacier is presently 0.35 km2 in area Overviews of LIA dating studies at 275 glaciers in the and actively calving into Iceberg Lake (unofficial name).

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Fig. 1. Map showing location of Strathcona Provincial Park and study sites on Vancouver Island, British Columbia.

The downvalley LIA extent of the glacier is demarcated by a separated into three distinct components based on morphology, nested moraine complex consisting of eight terminal and position, and vegetation cover: (i) two inner, relatively barren, recessional moraines located on the north side of the lake, fresh-appearing moraines (Moraines 1–2), the second of which -300 m from the present glacier terminus (Fig. 3). (Moraine 2) is considerably larger and overrides the proximal An outlet stream divides the moraine complex into eastern face of Moraine 3; (ii) a middle suite of three sparsely lichen- and western components. The eastern group of moraines and tree-covered moraines (Moraines 3–5), with the outer- have been heavily disturbed by snow avalanche activity and most of the three (Moraine 5) being the most prominent; were not extensively studied. In contrast, the western moraines and, (iii) an outer suite of three smaller, forested moraines have a more complete vegetation cover suitable for sampling (Moraines 6–8). and dating and were the focus of study at this site. Moraines 1–5 are composed predominantly of gravels and The arcuate western moraine complex is -100 m wide boulders, with limited soil development. Moraines 1, 3 and 4 and extends for -560 m from the bedrock face of Mount are relatively small (-1 m tall), consisting of primarily angular Colonel Foster (1200 m asl) to the outlet stream draining cobbles (<0.5 m diameter). The two most prominent moraines Iceberg Lake (980 m asl; Fig. 3). The moraine complex is (Moraines 2 and 5) are markedly larger (2–3 m tall) than the

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others and are composed primarily of large boulders (0.5– Table 1. Retreat distances and areal ice loss for Colonel 2 m diameter). Debris from the distal slope of Moraine 5 has Foster, Septimus and Moving glaciers. spilled downslope -3 m, partially burying extensive sections of Moraine 6. Immature mountain hemlock, subalpine fir, Retreat from LIA % of LIA maximum and yellow-cedar trees characterize tree growth on Moraines Glacier maximum (m) area remaining 1–5. The steepest eastern and western limits of the moraine Col. Foster 300 22 complex are dominated by alder (Alnus sp.) and willow (Salix Septimus 600 18 sp.) thickets. With the exception of Moraines 1 and 2, lichen Movinga 834 10 (Rhizocarpon sp.) are found on larger boulders throughout aFrom Smith and Laroque (1996). the moraine complex. Moraines 6–8 of the outer suite are soil covered, well- rounded and subdued (-0.5–1.0 m in height) relative to glaciological, and lichenometric techniques to determine the Moraines 1–5, and partially to completely overridden by limiting dates of discrete moraine-building episodes. Tree Moraine 5 at several locations. The outer moraines are colonized rings can provide an absolute age to these events where glaciers by a forest of mountain hemlock trees and are composed of have advanced into forest or where moraines support ade- sub-rounded cobbles and boulders (<0.5 m diameter). quate tree cover for dating (Luckman 1988; Smith and Laroque 1996; Lewis 2001). In treeless, high-elevation glacier Septimus Glacier forefields, however, minimum surface dates are determined us- Septimus Glacier is located 50 km southeast of Mount ing lichenometry (Luckman 1977; Smith et al. 1995). Tree- Colonel Foster on the northern flank of Mount Septimus near ring-based methods were used to date the more forested mo- the southern boundary of Strathcona PP (49°29′N, 125°32′W; raines of Colonel Foster Glacier, while a combination of both Fig. 1). Situated in a northwest-facing cirque at 1350 m, tree-ring and lichen dating techniques were employed at the Septimus Glacier has a present area of -0.08 km2 and is situated relatively treeless Septimus Glacier site. -600 m from four nested moraines located above the southeast shore of Cream Lake at 1261 m asl (Fig. 4). A branched outlet Dendrochronological and dendroglaciological techniques stream breaches the moraines, dividing the complex into All living trees found growing on moraine crests in both eastern and western components. glacier forefields were sampled to provide a minimum age of moraine establishment. Increment borers angled downwards A suite of four distinct moraines (Moraines 1–4) extend towards the root crown were used to extract samples that -700 m along the northeast side of the cirque from 1275 to were later age-dated by counting the number of annual tree 1600 m asl. Moraine 1 is represented here by two small rings using a Velmex-type measuring stage and a Wild M3B ridges (-0.5 m high), composed of small angular gravels stereomicroscope. The age of subfossil wood samples was (0.05–0.20 m diameter). Moraine 2 extends for -320 m and determined by cross-dating to one of three local living tree-ring is composed of large cobbles and boulders (0.2–1.0 m diameter). chronologies developed using standardized techniques (Fritts The crest of the moraine appears to have been disturbed or 1976; Schweingruber 1988; Stokes and Smiley 1996). Visual partially reworked in its upper reaches by avalanche activity. comparison of marker years and verification procedures within Snow-damaged krummholtz are present along the upper the COFECHA software program were used to establish 175 m of the moraine, with lichen (Rhizocarpon sp.) present absolute perimeter dates (Holmes 1999; Grissino-Mayer 2001). along the entire moraine. Moraine 3 extends for the entire Moraine dates assigned by tree rings remain uncertain until length of the lateral moraine complex, but becomes discon- corrections are made for pith errors, sampling height, and local tinuous and fragmented at its lower, northerly limit where it ecesis interval (Sigafoos and Hendricks 1969; Smith et al. is bisected by the outlet streams. Similar in composition and 1995; Villalba and Veblen 1997). Pith errors arise when appearance to Moraine 2, lichen thalli are relatively abundant increment core samples that did not intercept the pith (i.e., on the larger cobbles and boulders found along the moraine off-pith) are used to provide a minimum surface age (Sigafoos crest. Moraine 4 is located -10–20 m distal to Moraine 3, and Hendricks 1972). If it was determined during a field has only a sparse cover of snow-damaged mountain hemlock inspection that a sample was off-pith, where possible additional trees and krummholtz, and is composed primarily of boulders cores were extracted until the pith was intercepted. In instances (0.5–4.0 m diameter). where the pith was still not sampled (n = 5 trees), a standardized Lateral moraines along the western perimeter of the site correction factor based on ring-width and ring-curvature data are discontinuous and broken by a large, steep bedrock outcrop was employed to estimate the number of missing rings (Apple- starting -250 m upglacier from the terminal moraine. Fragments quist 1958; Norton et al. 1987; Villalba and Veblen 1997). of two ridges, interpreted as equivalent to Moraines 3 and 4, Sampling-height errors arise when annual growth rings are found at 1350 m and 1375 m asl (Sites B and A respec- are lost due to sampling above the root crown (McCarthy et tively; Fig. 4). Protruding boulders on both ridges have al. 1991). Application of a coring height–age correction factor sparse lichen cover, and tree growth is limited to young, required an assessment of the general rate of apical growth shrubby mountain hemlock, subalpine fir, and yellow-cedar (Villalba and Veblen 1997). This was established by destructive krummholtz interspersed with alder seedlings and saplings. sampling and measurement of 10 mountain hemlock saplings at Colonel Foster Glacier. It was determined that their mean Methods apical growth rate was 2.7 cm/year in this setting, a rate similar to that determined during a concurrent study 80 km to The LIA history of Colonel Foster and Septimus glaciers the south (Laroque et al. 2001). In this study, when trees is developed by applying dendrochronological, dendro- found growing on the moraines were sampled above the root

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Fig. 2. Moraine frequency histograms for glaciers of the Pacific Northwest. (a) Canadian Rockies, (b) Alaska, (c) coastal British Co- lumbia, and (d) Washington State. In the Biritsh Columbia histogram, dark grey boxes represent the Vancouver Island data, and the as- terisk represents the moraines deposited prior to 1397 A.D. Note the scale change for Washington State.

crown, a sampling height correction corresponding to the Foster (Evans 1989) provided a location for deriving a site- height of the core was applied (0.37 years/cm). As most sam- specific ecesis interval. A local mountain hemlock ecesis ples were taken at the stem base, the sampling height correc- correction factor was determined from 13 mountain hemlock tion factor was limited to a small number of trees. trees found growing on a bedrock surface stripped bare in The ecesis interval, or the time between surface stabilization the spring of 1946 by a displacement wave originating in and the germination of the first seedling, has been shown to Landslide Lake (Fig. 5). The oldest tree sampled at this site range from 1 to 100 years in the Pacific Northwest (Sigafoos in 1998 had a basal ring count of 48 years and indicates an and Hendricks 1961, 1969, 1972; Desloges and Ryder 1990; ecesis interval of four years should be added to the age of all McCarthy et al. 1991; Smith et al. 1995; Wiles et al. 1999; trees used to date moraine surfaces at Colonel Foster and Luckman 2000). Surface dates derived from the age of the Septimus glaciers. oldest tree found growing at a site must necessarily incorpo- rate a ecesis correction factor (Heusser 1956; Sigafoos and Lichenometric techniques Hendricks 1969; McCarthy and Luckman 1993). For this A locally calibrated lichen growth curve relating lichen study, an earthquake-induced landslide from Mount Colonel size to substrate age was developed to provide additional

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Fig. 3. Site map of the Colonel Foster Glacier study area highlighting the location of the western moraine complex.

absolute dating control (Beschel 1973; Luckman 1977; Innes The minimum substrate age of individual moraines was 1988). A local lichen dating curve was necessary as the determined by sampling each ridge crest in its entirety and nearest extant Rhizocarpon geographicum spp. curves (Fig. 6) measuring all lichen (A and B axes) to the nearest ±0.1 mm. either display markedly different growth characteristics (Porter Sampling was limited to near-circular lichen to avoid ano- 1981; Smith and Desloges 2000) or are not long enough to malously large or coalesced thalli (McCarthy and Smith 1995), date surfaces deposited prior to the early 1800s. The lichen and individual thalli were classified according to A-axis growth curve for Strathcona PP was developed primarily measurements. The largest lichen on each moraine was then from lichen measured growing on gravestones in the Cumber- used to determine the minimum substrate age from the dating land Community Cemetery (160 m asl) and from tree-ring- curve. Lichen samples returned to the University of Victoria dated moraines (e.g., McCarthy and Smith 1995; Smith et al. were identified to the species level as Rhizocarpon geo- 1995) at Septimus and Colonel Foster glaciers (Table 2). graphicum spp. Additional dating controls for the lichen growth curve were A local lichen ecesis interval was determined by measuring incorporated from 100 thalli measured on the 1958 Strath- all lichen thalli on dated surfaces at the Cumberland Community cona Hydroelectric Dam (201 m asl), and 50 thalli measured Cemetery. Visible and measurable lichen were only found on on boulders and bedrock from the 1946 Mount Colonel Foster surfaces over three years of age (Table 2). Given that the landslide scar below Landslide Lake (880–905 m asl; Table 2) early stages of lichen establishment are often inconspicuous The resulting lichen growth curve for Strathcona PP spans to the naked eye, a measurement of 0 mm does not indicate the interval from 1708 to 1998 A.D. (Fig. 6). a lack of lichen but rather a macroscopic presence–absence

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Fig. 4. Site map of the Septimus Glacier study area showing the location of the moraines and tree-ring dating sites.

indicator (O’Neal and Schoenenberger 2003). Consequently, 1 to 6 (Table 3). However, the 250- to 325-year-old trees the ecesis interval for R. geographicum spp. in this region found growing on the surfaces of Moraines 7 and 8 offer little was determined to be between 0 and 3 years. insight into the age of the moraines, as they are younger than the age of the more proximal Moraine 6 (Table 3). Results A tilted and partially rotted stump found in growth position on the distal face of Moraine 6 was partially buried by debris All surface dates presented here are considered to have an spilled distally from Moraine 5. A strong cross-date for the error range of ±10 years given the brevity of the ecesis intervals outermost 122 rings (r = 0.59, r > 0.3281 is significant at the for both lichen and trees. 99% confidence level) provides a kill date of 1750 A.D. and an uncorrected germination date of 1435 A.D. Corrections Colonel Foster Glacier for sampling height and ecesis suggest a minimum surface Our investigations at Colonel Foster Glacier focused primarily date of 1397 A.D. for Moraine 6 (Table 3). A distinctive scar on 54 living trees found growing on the moraines, with dated to 1696 A.D. and subsequent reaction wood (Fig. 7) additional information from a single in situ stump found mark the episode when the tree was impacted, pushed over, partially buried on the crest of Moraine 6 (Figs 3). Pith ages and partially buried by debris from the emplacement Moraine from the oldest living trees provide minimum dates for Moraines 5 at the end of the 17th century (Table 3).

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Fig. 5. Aerial photograph showing the location of the ecesis study site and its relative position to the Colonel Foster Glacier study site (National Air Photo Library of Canada, NAPL 30BC78 076 235, 1978).

Our lichenometric investigations at Colonel Foster Glacier moraine deposition prior to 1397 A.D. (early-LIA?) responsible are more equivocal. For example, the lichenometric date for for the deposition of Moraines 8, 7, and 6; (ii) a second episode Moraine 1 overestimates the moraine age by 33 years, whereas that culminated with the deposition of the prominent Moraine the dates for Moraines 2 and 4 underestimate the tree-ring 5 between 1690 and 1708 A.D.; (iii) a pair of smaller push dates by 35 and 77 years, respectively (Table 4). Consequently, moraines (Moraines 3 and 4) dated to 1700 and 1778 A.D. only the tree-ring dates for Moraines 3 and 5 are corroborated suggest the glacier may have remained at an advanced state by the lichenometric dates. The discrepancy in surface dates during the late 1700s; (iv) the relatively large Moraine 2 at Colonel Foster Glacier may be a result of lingering snow- identifies a final late-LIA advanced position of the glacier packs at this more protected site. Nevertheless, the corres- that ended by 1898 A.D.; and, lastly, (v) a stillstand or minor pondence of both lichen and tree-ring dates at Moraines 3 re-advance in the mid 1930s is recorded by Moraine 1 as the and 5 bolster evidence for the identification of glacial advances glacier retreated from its late 19th century advanced position. in the late 17th and 18th centuries (Table 4). Dating results from Colonel Foster Glacier identify five Septimus Glacier episodes of LIA glacier activity (Figure 8a): (i) a period of Insights from tree-ring data at Septimus Glacier come from

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Fig. 6. The Strathcona R. geographicum dating curve (solid line) techniques. Results from the lichenometric component of compared to the two existing growth curves from the Pacific this study provide the first lichen growth curve (1708– Northwest. Circles are tombstone dates, triangles are tree-ring 1998 A.D.) for Vancouver Island. This growth curve fills dated surfaces, and stars are independent control points from the the gap between existing dating curves to the south (Mt. 1958 Strathcona Dam and the 1946 landslide scar. Rainier, Washington State) and north (Bella Coola, B.C.). While similar to the Mt. Rainier growth curve and approxi- mately half the growth rate of the Bella Coola curve, the Strathcona lichen curve spans a greater interval (290 years vs. 125 and 165 years, respectively). The location and length of this dating curve provides a significant measure of confidence for further lichenometric studies in this region. Our lichenometric investigations also show that the ecesis interval for R. geographicum spp. in this setting is very brief at only three years. Equally brief is the ecesis interval of four years for the establishment of mountain hemlock trees. The brevity of these ecesis intervals greatly reduces one of the main uncertainties in using geobotanical methods for dating late Neoglacial landforms. The moraine dates provided, therefore, give a good approximation of the shift in climate conditions that lead to the retreat of the glaciers and subsequent stabilization of the moraines. The LIA moraine records at Colonel Foster and Septimus glaciers expand upon earlier investigations in Strathcona PP at Moving Glacier by Smith and Laroque (1996). Evidence for LIA activity prior to 1400 A.D. is limited to the outer suite of moraines at Colonel Foster Glacier, whereas both Colonel Foster and Septimus glaciers appear to have responded in a synchronous manner to major moraine-building episodes in the early 1700s and late 1800s, as evidenced by the prominent 15 trees sampled at two locations (Fig. 4). Moraines 2 and 3 moraines at each site (Figs. 8a,8b; Table 7). Dendro- were dated using trees collected at the upper stand of trees glaciological results from Moving Glacier also identify a (site A), while Moraine 4 date was from the lower stand of corresponding LIA advance in the early 1700s (Smith and trees (site B). Although no trees were found growing on Laroque 1996). A minor moraine-building episode in the Moraine 1, tree-ring-derived minimum surface dates for mid 1930s is also recorded at both Colonel Foster and Septimus Moraine 2 (1898 A.D.), Moraine 3 (1874 A.D.), and Moraine glaciers (Figs. 8a,8b; Table 7). While the timing of these 4 (1710 A.D.) indicate that these moraines are late-LIA features three events is comparable, the late 19th century advance at (Table 5). This interpretation is supported by our licheno- Colonel Foster Glacier and mid 19th century advance at metric data, which place the stabilization of the Septimus Septimus Glacier may have overrode and reworked evidence Glacier moraines within similar time frames as those established of previous advances, thereby making direct comparisons of by our tree-ring data (Table 6). The single largest mean the moraine records for these intervals somewhat difficult. thalli diameter from each moraine was only 2.8%–3.9% larger The Vancouver Island LIA moraine history compares well than the mean of the five largest from the same moraine. the existing record of LIA glaciation along the Washington– This indicates that the single largest lichens were not an- British Columbia–Alaska transect (Fig 1). Although limited omalously large and, therefore, provide reasonable stabiliza- in sample size, the glacial record from Vancouver Island is tion dates in this largely treeless setting (Table 6). similar to moraine chronologies from surrounding regions The LIA moraine history at Septimus Glacier indicates (Fig. 2). The presence of early-LIA moraines at Colonel four general episodes of LIA glacial activity (Fig. 8b): (i)a Foster Glacier suggests that the deposition of these moraines late 17th century advance that culminated with deposition of were coeval with early-LIA moraines documented elsewhere Moraine 4 by -1706 A.D., marking the greatest downvalley in British Columbia, Alaska, and Washington State. The early extent of the glacier; (ii) a readvance in the mid- to late 18th and late 19th century moraine dates from Vancouver 1700s that ended with the deposition of Moraine 3 by Island correspond very well to the widespread mid- to late-LIA 1836 A.D.; (iii) a final readvance of the glacier in the mid response of glaciers throughout western Canada, Alaska, and 1800s, terminating by 1898 A.D. with the deposition of Washington State (Fig. 2). Although the timing of maximum Moraine 2, the most prominent of the four moraines; and, LIA positions may differ between sites, the congruent finally, (iv) a minor readvance or stillstand that ended prior behaviour of glaciers within these regions suggests that they to 1934 is recorded by Moraine 1. have, at some level, been responding in a synchronous manner to similar large-scale climatic forcing. Conclusions The emerging record of LIA moraine-deposition events on Vancouver Island serves to highlight the varied effect of two LIA glacier activity in Strathcona Provincial Park was levels of glacier response: (i) a response to persistent large- investigated using both lichenometric and dendrochronological scale climate forcing that culminated with the synchronous

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Table 2. Control point data for the Strathcona Rhizocarpon growth curve. Elevation Largest lichen Control point Substratea (m asl) (mm) Substrate date 1 Tombstone 165 3.2 1995 2 Tombstone 165 11.8 1988 3 Tombstone 165 10.1 1987 4 Tombstone 165 11.9 1983 5 Tombstone 165 13.4 1982 6 Tombstone 165 15.7 1981 7 Tombstone 165 18.7 1978 8 Tombstone 165 22.2 1976 9 Tombstone 165 23.9 1971 10 Tombstone 165 22.6 1969 11 Tombstone 165 22.2 1967 12 Tombstone 165 20.9 1965 13 Tombstone 165 27.1 1953 14 Tombstone 165 29.7 1943 15 Tombstone 165 31.0 1934 16 Tombstone 165 36.5 1932 17 Tombstone 165 32.7 1931 18 Tombstone 165 34.1 1929 19 Tombstone 165 34.0 1926 20 Tombstone 165 36.0 1916 21 Tombstone 165 36.5 1915 22 Tombstone 165 40.2 1909 23 Landslide Scar 990 32.8 1946 24 Strathcona Dam 210 25.6 1958 25 Moraineb 1225 42.7 1898 26 Moraineb 1325 97.4 1710 27 Morainec 1265 96.6 1708 28 Morainec 1220 78.0 1778 aAll tombstones are from the Cumberland Community Cemetery. bMoraine 4 at Septimus Glacier. cMoraine 5 at Colonel Foster Glacier.

Table 3. Tree ages and minimum surface dates for two glaciers responded asynchronously to local variables, such moraines at Colonel Foster Glacier. as microclimate, slope, aspect, size, and shape of the glacier, bedrock slope, and whether or not the glacier terminates in a No. of trees Oldest living Minimum a water body. Above this threshold, however, local factors be- Moraine sampled tree (years) surface date come secondary to a stronger, regional climate signal and 1 9 59 1935 the glaciers appear to have responded in a synchronous manner. 2 9 96 1898 The “bi-modal” response appears not to be limited to 3 11 216 1778 Vancouver Island glaciers, as similar response patterns for 4 7 224 1770 glaciers in the southern British Columbia Coast Mountains 5 8 286 1708 have recently been documented by Larocque and Smith (2003) 6 5 403 1591 (1397)b in the Mount Waddington area. 7 3 250 1744 8 5 325 1669 aSurface date includes 4-year ecesis interval. bBracketed date is from the buried stump on Moraine 6. Acknowledgments We thank Eric Leonard and Tracy Brennand for their deposition of the larger 1708 and 1706 A.D. and 1898 A.D. comments and suggestions on the original manuscript, moraines, and smaller mid-1930s moraine; and (ii) a response University of Victoria Tree-Ring Laboratory staff for their to smaller scale events that likely record advances that were assistance in the field and laboratory, and Sarah Boon for ultimately governed by local factors. These small-scale events reviewing a revised version of the manuscript. This research are associated with the asynchronous deposition of the 1770 was funded by a grant (# 138966) from the Natural Sciences and 1778 A.D. moraines at Colonel Foster and the 1836 A.D. and Engineering Research Council of Canada to D. Smith. moraine at Septimus Glacier (Figs. 8a,8b; Table 7). These Permission to work in Strathcona Provincial Park was granted findings suggest that below a certain climate threshold, the by B.C. Parks.

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Fig. 7. Photograph of the stump cross-section showing key event dates. Scale = 1:3.

Table 4. Lichen dating results for the moraines at Colonel Foster Fig. 8. Schematic of moraine cross-sections at (a) Colonel Foster Glacier; tree-ring-derived surface dates included for comparison. Glacier and (b) Septimus Glacier. Moraine number is indicated by circled numbers, and dashed lines indicate synchronously Minimum surface deposited moraines. Not to scale. date No. of Largest single Lichen Tree Moraine lichen lichen (mm) derived derived 1 17 39.3 1912 1935 2 8 33.5 1933 1898 3 48 78.0 1775 1778 4 7 57.4 1847 1770 5 63 96.6 1708 1708

Table 5. Tree ages and minimum surface dates for moraines at Septimus Glacier. No. of trees Oldest living Minimum Moraine sampled tree (years) surface datea 10 — — 2 5 96 1898 3 4 120 1874 4 7 284 1710 aSurface date includes 4-year ecesis interval.

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Table 6. Lichen dating results for the moraines at Septimus Glacier; tree-ring-derived surface dates included for comparison. Minimum surface date Average of No. of Lichen 5 largest Single largest Lichen Tree Moraine sampled (mm) (mm) derived derived 1 31 31.9 33.2 1934 — 2 60 41.5 42.7 1898 1898 3 78 58.7 60.8 1836 1874 4 95 93.6 97.4 1706 1710

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