Canadian Journal of Earth Sciences

Long-Term Nivation Rates, Cathedral Massif, Northwestern

Journal: Canadian Journal of Earth Sciences

Manuscript ID cjes-2019-0176.R2

Manuscript Type: Article

Date Submitted by the 25-Mar-2020 Author:

Complete List of Authors: Nyland, Kelsey; Michigan State University, Department of Geography, Environment, and Spatial Sciences; George Washington University, Geography Department Nelson, Frederick; Michigan State University, Department of Geography, Environment,Draft and Spatial Sciences; Northern Michigan University, Department of Earth, Environmental and Geographical Sciences

Periglacial Geomorphology, Nivation, , UAV Survey, Keyword: Volumetric Estimation, Denudation Rates

Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? :

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1 2 3 4 5 6 7 8 9 10 11 12 13 LONG-TERM NIVATION RATES, CATHEDRAL MASSIF, 14 NORTHWESTERN BRITISH COLUMBIA 15

16

17

18 Draft

19 Kelsey E. Nyland ([email protected])1,2 Frederick E. Nelson ([email protected])2,3

20 1Department of Geography, The George Washington University, Washington, DC, USA 21 Mailing Address: 2036 H St., NW, Washington, DC, 20052

22 2Department of Geography, Environment, and Spatial Sciences, Michigan State University, East 23 Lansing, Michigan, USA 24 Mailing Address: 673 Auditorium Rd., East Lansing, MI, 48824 25 3Department of Earth, Environment, and Geographical Sciences, Northern Michigan University, 26 Marquette, Michigan, USA 27 28 29 30 Corresponding author: 31 Kelsey E. Nyland, Department of Geography, The George Washington University, 2036 H St., 32 NW, Washington, DC, 20052, USA 33 Telephone: 603-562-7023 34 Fax: 202-994-2484

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35 Abstract: Cryoplanation terraces (CTs) are large (3000-800,000 m2), erosional landforms found

36 in upland periglacial environments. Two hypotheses for the formation of CTs are supported in

37 contemporary literature: 1) CT formation is controlled primarily by geologic structure; and 2)

38 CTs are climatically controlled through nivation, a suite of erosional processes associated with

39 late-lying snowbanks. A persistent question in periglacial geomorphology is whether nivation

40 can produce CT-scale landforms. This paper examines the unique deglaciation history of “Frost

41 Ridge” on the Cathedral Massif, northwestern British Columbia, to estimate long-term

42 denudation attributable to nivation processes active since the last glacial maximum. Frost Ridge

43 forms one flank of an east-west oriented glacial valley. During deglaciation, marginal drainage

44 created V-shaped erosional notches on both valley walls. Minimization of solar radiation on the

45 steep north-facing wall (Frost Ridge) allowedDraft snowbanks to accumulate and persist in the

46 marginal drainage features and nivation processes to erode the slope. Today, several large

47 nivation hollows (incipient cryoplanation terraces) are present near the summit of Frost Ridge,

48 while the V-shaped marginal drainage features are preserved at lower elevations and on the

49 opposite, south-facing valley wall. A high-resolution survey using an unmanned aerial vehicle

50 (UAV) allowed volumes of marginal drainage and incipient terrace features to be compared.

51 Based on this volumetric comparison, denudation rates are estimated to be from 4.2 to 125.8 mm

52 ka-1, which are comparable to relatively short-term nivation rates reported from Antarctica and

53 mid-latitude alpine periglacial areas.

54

55 Keywords: Periglacial Geomorphology, Nivation, Cryoplanation, UAV Survey, Volumetric

56 Erosion Estimation

57

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58

59 Introduction

60 Cryoplanation terraces (CTs) are large landforms consisting of alternating steep and

61 shallow slope segments and repeating sedimentological patterns (Demek 1969; Reger 1975). From

62 a distance, these landforms resemble immense staircases. Risers (scarps) are inclined at angles of

63 15° - 40° and display exposed bedrock or a veneer of coarse, angular, clastic rubble. The large

64 (3000-800,000 m2), gently sloping (1° - 10°) treads are mantled with sorted and

65 lobes. Although these landscape-scale features have long been associated with

66 periglacial environments, the geomorphic processes responsible for their formation remain

67 contentious. Debate is focused on whether CT formation is controlled primarily by geologic

68 structure or by climatic factors (FrenchDraft 2017, 295; Ballantyne 2018, 220-222). Process-oriented

69 field investigations on CTs are rare. There are, however, several indirect lines of evidence

70 supporting the climatic-influence hypothesis of CT development, through the suite of periglacial

71 and fluvial processes known collectively as nivation.

72 Nivation is a shorthand term for locally intensified weathering, transport, and depositional

73 processes associated with large snowbanks that persist well into summer months. The prolonged

74 thermal insulation and moisture provided by snowbanks promote chemical and mechanical

75 weathering through (e.g., Matsuoka and Murton 2008). Meltwater transports

76 eroded materials throughout the summer via rillwash, sheetwash, and piping, thereby also

77 promoting solifluction and frost creep (e.g., Thorn and Hall 1980, 2002; Berrisford 1991).

78 Indirect evidence indicating that nivation plays a critical role in CT formation includes CTs

79 that cut across geologic structure (e.g., Demek 1969; Reger 1975), statistically preferred poleward

80 orientations of CT scarps (Nelson 1998), CT elevation trends that closely track those of glaciers

81 (Nelson and Nyland 2017). Nonetheless, Demek’s (1969, 66) statement that “there are no data on

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82 the rate of development of cryoplanation terraces” remains as applicable to the contemporary

83 literature as it was a half-century ago.

84 One of the key remaining issues is whether nivation can produce landforms with the

85 dimensions typical of CTs. Although smaller related features are often called nivation hollows, we

86 follow a recommendation to separate morphological and genetic inferences (Thorn 1983) by

87 referring to cryoplanation landforms and nivation processes (Lewis 1939; Te Punga; 1956, 335;

88 Embleton and King 1968, 533).

89 This study addresses two fundamental, unresolved issues in cryoplanation research (cf.

90 Priesnitz 1988; Thorn and Hall 2002): 1) documentation of active nivation processes on

91 cryoplanation landforms; and 2) calculation of long-term denudation rates by nivation processes.

92 Frost Ridge constitutes a highly unusualDraft configuration of features developed under naturally

93 controlled conditions, resulting in terraces approaching the size of typical CTs found throughout

94 unglaciated Beringia. Insights into this active nivation environment are critical, as the CTs in

95 unglaciated Beringia, including those in nearby Yukon Territory, are considered by many to be

96 relict (e.g., Reger 1975; Reger and Péwé 1976; Hughes 1990, 14-16; Lauriol 1990).

97 Study Area and Geomorphic Evolution

98 This study evaluates the hypothesized link between long-term denudation rates by nivation

99 and the size and morphology of incipient cryoplanation terraces, also known as transverse nivation

100 hollows (Lewis 1939), on the Cathedral Massif in the Atlin / Téix’gi Aan Tlien Provincial Park,

101 40 km southwest of the village of Atlin in northwestern British Columbia (Figures 1 and 2).

102 Periglacial slope evolution on the northerly aspect of Frost Ridge (N 59° 21’ 5’, W 134° 5’) is the

103 focus of this work. Atlin is within the zone of sporadic, discontinuous (10 to 50% of

104 area underlain by permafrost) characterized as having low (<10%) ground ice content within 10 to

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105 20 m of the ground surface particularly in upland/alpine locations (Heginbottom et al., 1995)

106 Bevington and Lewkowicz (2015) calculated that permafrost in the Atlin area is found only in

107 surrounding mountains. Ice-rich permafrost occurs above 925 m.a.s.l. in near Atlin (Tallman

108 1975). Nelson (1979) calculated that permafrost is widespread above 1220 m.a.s.l. in the Atlin

109 area and observed shallow permafrost on the north-facing slope of Frost Ridge at 1490 m.a.s.l..

110 Permafrost is likely, however, to have retreated upward in the four decades since those

111 observations were made. The Cathedral Massif is part of the Atlin Terrane and has been described

112 as a “coast intrusion” of the Coast Plutonic Complex made up of primarily porphyritic and

113 granophyric subvolcanic rock of Jurassic to Neogene age (Jones 1975; Nelson 1979; Gehrels et al.

114 2009).

115 Draft

116 [Figure 1 near here]

117 is a paleonunatak, formerly surrounded by the ancestral Hobo-Llewelyn

118 Glacier, part of the larger Cordilleran Ice Sheet (Bass 2007). The tributary of the ancestral Hobo-

119 Llewelyn Glacier that occupied the present Edgar Lake valley (Figure 1) receded between the

120 middle (ca. 25 ka) and late Wisconsinan (ca. 11 ka) (Jones, 1975, 35; Miller 1975, 131-132;

121 Slupetzky and Krisai 2009, 207).

122 During waning phases of the Wisconsinan glaciations, the upper reaches of Frost Ridge

123 stood above the level of the glacier then occupying the present-day Edgar Lake valley (informal

124 name). A large cryoplanation terrace and a small were incised into the flanks of Splinter

125 Peak (Figure 2A). The tread of this CT displays a well-developed field of sorted patterned ground,

126 consisting largely of sorted stripes (Figure 2B).

127

128 [Figure 2 near here]

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129

130 Edgar Lake valley is oriented east-west, with side slopes on Frost Ridge and Mt. Cameron

131 facing north and south, respectively (Figure 1). The north-facing flank of Frost Ridge displays a

132 series of visually striking subhorizontal lineations, sloping down-valley at 1.7o (Figures 2A and

133 2C). These features are currently occupied by deep accumulations of snow that remain well into

134 summer. Similar lineations occupy the opposite (south-facing) valley side (Mt. Cameron), but are

135 not occupied by late-lying snowbanks.

136 The series of elongated incisions subparallel with valley contours and past glacier flow are

137 consistent with descriptions of marginal drainage from deglaciation elsewhere (Maag 1969;

138 Embleton and King 1975, 338-344; Syverson and Mickelson 2009). Because solar radiation is

139 minimized on steep north-facing slopesDraft in the Northern Hemisphere, large transverse snowbanks

140 accumulated and persisted in these initially V-shaped incisions on Frost Ridge (Figure 2C). On the

141 north-facing valley wall the incisions were enlarged substantially by nivation and their profiles

142 modified to resemble the typically step-like form of CTs (Figure 2D). At lower elevations,

143 however, where snow does not persist as long into the summer, the initial form of the marginal

144 drainage features has been preserved. The developmental history of Frost Ridge topography is

145 represented in Figure 3. Slupetzky and Krisai (2009, 198) advanced an alternative explanation for

146 the genesis of the lineations, interpreting them as deposits of hummocky morainic and fluvioglacial

147 material that were subsequently modified extensively by periglacial processes.

148 St-Onge (1969) concluded that it is next to impossible to ascertain the extent to which

149 nivation processes have modified preexisting topographic irregularities, or whether they initiate

150 such irregularities. The unusual history of deglaciation on Frost Ridge and the topoclimatic

151 contrasts between the north- and south-facing slopes, mitigates this issue. The size and morphology

152 of the marginal drainage channels determined through straightforward measurements and

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153 comparison with those of the contemporary (modified) incipient terraces upslope, provides a frame

154 of reference within which long-term nivation erosion rates can be estimated in a historical context.

155 156 [Figure 3 near here] 157

158 Methods

159 Nivation Observations 160 Active nivation processes were observed and recorded in late July of 2017 and 2018. Three

161 of the large, late-lying snowbanks occupying incipient terraces on the north side of Frost Ridge

162 were surveyed with a handheld GPS and three snow pits were excavated in a transect bisecting the 163 approximate middle of each snowbank. DraftTemperature and density measurements were recorded at 164 regular intervals down snow profiles and notes were taken on any ice structures present, focusing

165 on conditions at the base of the snowbank.

166 In July 2018, the snowbanks were surveyed again, and three meltwater samples were

167 collected from the downslope margin of each snowbank, following the procedure outlined by

168 Ballantyne (1978). At the lower edge of the snowbanks, the time to fill 2-litre bottles with

169 meltwater and waterborne sediment was recorded. Air and soil surface temperatures were recorded

170 during the collection of each sample.

171 Analysis of these samples was performed at a Michigan State University soil lab. Samples

172 of meltwater and sediment were weighed, and dissolved content was measured using an Apera

173 Instruments, AI422-M EC400S conductivity meter. Samples were then dried, lightly ground, and

174 sieved (2 mm) to separate coarse and fine earth fractions. Particle size analysis for the fine fraction

175 was performed by laser diffraction using a Malvern Mastersizer 2000E unit. Fines were

176 homogenized using a sample splitter and a mass of approximately 2 g was chemically dispersed in

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177 a water-based solution of [NaPO3]13·Na2O that was then shaken for at least 40 min. Laser

178 diffraction generated detailed particle size measurements and precise textural classification.

179 Volumetric Comparison of Marginal Drainage and Incipient Terraces 180 Returning to Frost Ridge on 4 September 2018, when ablation of the snowbanks was

181 complete, we conducted an unmanned aerial vehicle (UAV) survey to generate a high-resolution

182 digital elevation model (DEM) of the north-facing flank of Frost Ridge. A DJI Mavic 2 Pro was

183 flown over two adjoining areas covering a total of 1.3 km2. Using DJI mission planning software,

184 the UAV was flown with the camera oriented to nadir at approximately 80 m altitude in a grid

185 pattern, with flight lines oriented northeast-southwest every 25 m. Exposure intervals coupled with

186 the flight line spacing resulted in 75% front and side overlap between images. Four ground control

187 points were collected using a handheld GPS,Draft at two low-elevation locations within the area covered

188 and two high-elevation locations (where the UAV took off and landed for both flights). Photos

189 were processed and photogrammetry performed in Pix4Dmapper (Pix4D Inc., San Francisco,

190 California), which generated DEMs with spatial resolutions of 6.10 cm2 (east area) and 5.84 cm2

191 (west area). Absolute geolocation variance in all three dimensions was < 0.9 m. The accuracy of

192 the DEM was deemed acceptable because subsequent analysis is more dependent on relative rather

193 than absolute landform positions and morphologies.

194 Coordinates taken at incipient terraces and marginal drainage features of interest were used

195 to identify these features on the DEM in ArcMap 10.2.2. One-hectare extractions of the three

196 incipient terraces and six segments of the highest-elevation marginal drainage feature were

197 resampled via cubic convolution to 25 cm2 spatial resolution for computational ease. Differences

198 in volume were computed in Surfer v. 12 (Golden Software 2014) software using triangulated

199 irregular network interpolations of the DEMs.

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200 Calculation of Nivation-Driven Denudation Rates 201 Denudation rates were calculated by dividing the eroded volume by area of eroded material

202 and dividing by the temporal deglaciation envelope published previously for this ancestral

203 tributary of the Hobo-Llewellyn glacier (Jones 1975, 35; Miller 1975, 131-132; Slupetzky and

204 Krisai 2009). This procedure yielded a maximum denudation rate, based on the later bound of the

205 deglaciation envelope (11 ka), and a minimum rate based on an earlier bound (25 ka).

206 Results

207 Active Nivation Processes on Frost Ridge 208 The collective periglacial and fluvial processes constituting the nivation process suite

209 continue to operate on Frost Ridge, as evidenced by thermal, erosional, and other general

210 observations documented in late July 2017Draft and 2018. Late-lying snowbanks provide consistent

211 sub-zero temperatures to underlying rock material through July (Figure 4). Basal ice, ranging from

212 1 cm to 9.5 cm thick, was found at the bottom of the snowpack in all snow pits. Temperatures in

213 the snowpack ranged from -0.5 to -3° C (Figure 4). Running water was clearly audible within the

214 snow pits, flowing through interstitial spaces beneath.

215

216 [Figure 4 near here]

217 Meltwater samples (a through c) taken from areas of notable rill and sheet flow from the

218 downslope margins of the three snowbanks in late-July 2018 helped to characterize sediment

219 fluxes (Table 1). The transported material ranged from dissolved solids to gravels (maximum

220 gravel diameter collected was 38 mm). The majority of mass in transit consisted of coarse silt to

221 medium sands.

222 [Table 1 near here]

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223 Volumetric Comparison of Landforms

224 Three-dimensional representations of the marginal drainage (MD) features and incipient

225 terraces (IT) are shown in Figure 5. The incipient terrace scarps are from 9 to 25 m high, with

226 slopes from 20 to 35°. Treads are from 30 to 75 m in length perpendicular to the contour, with

227 slopes of less than 20°. The marginal drainage features have distinct reverse slopes (Figure 2C),

228 and the typical V-shaped profiles associated with fluvial erosion.

229 [Figure 5 near here]

230 Assuming the marginal drainage features at lower elevations represent the approximate

231 shape and size of the original landforms immediately after deglaciation, differences between these 232 and the modified features upslope provideDraft estimates of the volume of material eroded by nivation 233 processes since deglaciation (Figure 5). Comparisons were performed for all combinations of the

234 six marginal drainage features and three incipient terraces. All eroded volumes and areas are

235 reported in Table 2.

236 [Table 2 near here] 237 238 239 Nivation-Driven Denudation Rates

240 Denudation rate estimates based on eroded volume, area eroded, and published temporal

241 deglaciation “envelope” for Frost Ridge, are shown in Table 3. Several authors have reported mid-

242 to late-Wisconsinan deglaciation chronologies for Edgar Lake valley (Jones 1975, 35; Miller 1975,

243 131-132; Slupetzky and Krisai 2009, 207). We therefore used bounds of 25 ka and 11 ka to

244 generate minimum and maximum possible denudation rates for these features. Calculated

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245 denudation rates for Frost Ridge range from 1.6 to 33.6 cm ka-1. The average rate is 9.4 cm ka-1

246 (8.9 cm ka-1 if the extreme value of 33.6 is omitted).

247 [Table 3 near here]

248 Discussion and Conclusions

249 The size and morphology of the incipient terraces observed on Frost Ridge, and particularly

250 of IT2 and IT3, approach those of what have been described as “well-developed” CTs in eastern

251 Beringia and elsewhere (e.g., Demek 1969; Reger 1975). CTs have been summarized as typically

252 having treads from tens to hundreds of meters perpendicular to the contour, with gradients < 10°

253 and scarps 15 to 40° rising tens of metres high (Ballantyne 2018, 200). 254 Volumetric comparisons (FigureDraft 5 and Table 2) indicate that the initial reverse slopes have 255 completely eroded and that possible infilling occurs largely at the toes of the incipient terrace

256 treads as these surfaces assume shallower slopes over time (Figure 5A). Calculated denudation

257 rate estimates based on these volumetric differences (Table 3) are comparable with other works

258 published for active nivation in unconsolidated material. For example, Thorn (1976) reported a

259 nivation erosion rate of 7.5 mm ka-1 (0.75 cm ka-1); Rączkowska reported (1995), 4 to 640 cm ka-

260 1; Kňažková et al. (2018) estimated 77 ± 12 cm ka-1, and Matthews et al. (2019) reported a

261 maximum rate of ~10 cm ka-1. Although the denudation estimates reported here are similar to

262 published nivation rates, the variability in results and differences in local geology of these study

263 areas indicates that more research is needed before deterministic modeling of these processes can

264 be attempted.

265 The circumstances of deglaciation in the Edgar Lake valley constitute a relatively well-

266 controlled natural field experiment on Frost Ridge. This work establishes that Frost Ridge is an

267 active nivation environment in which large, late-lying snowbanks are present at high elevations

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268 typically through the month of July. The snowbanks were observed actively eroding the underlying

269 unconsolidated materials. Nivation acting over long periods on this slope has likely transported

270 significant volumes of material off these treads, contributing to terrace formation with denudation

271 rates ranging from 1.6 to 33.6 cm ka-1 based on the volumetric comparisons.

272 The proximity of the ridge to local alpine glaciers means it shares the hypothetical climate

273 space defined by mean annual temperature and precipitation required by both and CTs

274 (Nelson 1989, 39). The conditions defining the climate space are similar to those during

275 Pleistocene cold intervals, when CTs are thought to have been actively forming across Beringia

276 (Nelson and Nyland 2017). We interpret Frost Ridge as being in an area of active CT development,

277 and a location at which the repeated calls for long-term process monitoring can be addressed (e.g.,

278 Demek 1969; Prieznitz 1988; Thorn andDraft Hall 2002; Nelson and Nyland 2017).

279 Future work at this site will include analysis of data from sediment traps, thermal and soil

280 moisture data loggers, and hydrological instruments installed during 2019 across incipient terrace

281 treads. Whether the initial V-shaped slope profiles were modified entirely by erosion or partially

282 by infill (Cairnes 1912; Eakin 1916, 81) remains to be determined. Repeat UAV surveying using

283 differential GPS and deployment of stable isotope tracers, will be used to monitor and better

284 understand the nivation processes occurring on Frost Ridge. Future work will also include

285 geochronology studies to refine the glacial history of the Cathedral Massif and Edgar Lake valley

286 using techniques such as cosmogenic nuclide dating.

287

288

289

290 Acknowledgements

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291 This research was in collaboration with the Research Program, through its Camp

292 29 facility in the Cathedral Massif. The work was funded through grants to K.E. Nyland from the

293 Geological Society of America’s Graduate Student Research Grant program, the Arctic Institute

294 of North America’s Grants-in-Aid program, and summer research fellowships from the College

295 of Social Science at Michigan State University. We thank Clayton Queen, Raven Mitchell, and

296 Christopher Cialek for their help with data collection. K.E. Nyland’s dissertation guidance

297 committee, consisting of committee co-chair, Dr. Randall Schaetzl, and Drs. Ashton Shortridge,

298 David Lusch, and Grahame Larson provided incisive criticism and helpful suggestions. F.E.

299 Nelson expresses gratitude to the late Professor Robert L. Nichols of Tufts University for the

300 original interpretation of the landforms as marginal drainage features, and for lengthy

301 discussions at Camp 29 during August 1976.Draft We thank Drs. Timothy Fisher (University of

302 Toledo) and Heinz Slupetzky (University of Salzburg) for reviews leading to improvements to

303 the paper. We are also grateful to Norm Graham (Discovery Helicopters Ltd.) and Fionnuala

304 Devine (Merlin Geosciences Inc.) for helicopter and drone piloting and photogrammetry post-

305 processing.

306

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380 Physical Geography, 80: 135-151. Draft 381 Nelson, F.E., Nyland, K.E. 2017. Periglacial cirque analogs: elevation trends of cryoplanation

382 terraces in eastern Beringia. Geomorphology, 293: 305-317.

383 Prieznitz, K. 1988. Cryoplanation. In Advances in Periglacial Geomorphology. Edited by M.J.

384 Clark. John Wiley & Sons Ltd: Chichester. pp. 49-67.

385 Rączkowska, Z. 1995. Nivation in the high Tatras, Poland. Geografiska Annaler: Series A,

386 Physical Geography, 77: 251-258.

387 Reger, R.D. 1975. Cryoplanation Terraces of Interior and Western Alaska. Ph.D. Thesis. Arizona

388 State University, Department of Geology, Tempe, AZ.

389 Reger, R.D., Péwé, T.L. 1976. Cryoplanation terraces: indicators of a permafrost

390 environment. Quaternary Research, 6: 99-109.

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391 Slupetzky, H., Krisai, R. 2009. Indications of Late Glacial to Holocene fluctuations of Cathedral

392 Massif Glacier, Coast Range (Northern British Columbia, Canada). Zeitschrift für

393 Gletscherkunde und Glazialgeologie, 43/44: 187-212.

394 St-Onge, D.A. 1969. Nivation Landforms. Geological Survey of Canada Paper 69-30: 1-12.

395 Streicker, J. 2016. Yukon Climate Change Indicators and Key Findings 2015. Northern Climate

396 ExChange, Yukon Research Centre, Yukon College, Whitehorse, Yukon.

397 Syverson, K.M., and Mickelson, D.M. 2009. Origin and significance of lateral meltwater

398 channels formed along a temperate glacier margin, Glacier Bay, Alaska. Boreas, 38: 132-

399 145.

400 Tallman, A.M. 1975. The Glacial and PeriglacialDraft Geomorphology of the Fourth of July Creek 401 Valley, Atlin Region, Cassiar District, Northwestern British Columbia. Ph.D. Thesis,

402 Department of Geology, Michigan State University, East Lansing, MI.

403 Te Punga, M.T. 1956. Altiplanation terraces in southern England. , 4:

404 331-338.

405 Thorn, C.E. 1976. Quantitative evaluation of nivation in the Colorado Front Range. Geological

406 Society of America Bulletin, 87: 1169-1178.

407 Thorn, C.E. 1983. Seasonal snowpack variability and alpine periglacial geomorphology. 408 Polarforschung, 53: 31-35.

409 Thorn, C.E., and Hall, K. 1980. Nivation: an Arctic-Alpine comparison and reappraisal. Journal

410 of Glaciology, 25: 109-124.

411 Thorn, C.E., and Hall, K. 2002. Nivation and cryoplanation: the case for scrutiny and

412 integration. Progress in Physical Geography, 26: 533-550.

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413

414 Table 1. Meltwater discharge rate and transported material characterization. Data on discharge

415 and sediment being transported away from the margins of the three late-lying snowbanks observed

416 in incipient terraces (IT- 1 through 3) on Frost Ridge.

Incipient Sample Total Gravel Fines % % % Discharge Average Terrace Dissolved (g) (g) Clay Silt Sand Rate Discharge Solids (m3h-1) Rate (mg/L) (m3h-1) a 7.77 13.98 38.24 18.3 64.6 17.0 3.15 x 10-3 1 b 6.84 31.46 128.6 13.6 39.2 47.1 1.48 x 10-3 1.88 x 10-3 c 3.27 0.5400 8.860 8.7 33.8 57.5 9.97 x 10-4 a 15.0 20.04 89.57 15.3 38.4 46.3 7.48 x 10-4 2 b 5.12 9.560 30.71 13.7 30.9 55.4 1.87 x 10-3 7.11 x 10-3 c 3.83 6.330 Draft18.95 9.2 43.3 47.5 1.87 x 10-2 a 5.82 123.4 132.0 3.0 16.6 80.4 19.7 x 10-2 3 b 11.5 51.54 126.3 5.6 25.9 68.5 12.1 x 10-2 13.5 x 10-2 c 7.85 21.03 87.34 7.7 29.5 62.8 8.55 x 10-2

417 418

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419

420 Table 2. Volume differences between marginal drainage and incipient terraces.

Incipient Terrace 1 2 3 Volume Eroded (m3) 36,659 26,374 11,601 1 Area Eroded (m2) 9,896 9,898 8,360 Volume 15,097 5,484 780 2 Area 9,759 7,922 1,839 Volume 17,498 7,859 2,688 3 Area 9,752 8,022 2,920 Volume 19,676 9,435 2,504 4 Area 9,869 9,494 4,035 Volume 22,462 13,467 6,586 5 Area Marginal Drainage Feature Marginal Drainage 9,882 7,664 5,633 Volume 15,342 6,047 1,094 6 Area Draft9,206 7,174 2,129 421 422

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423

424 Table 3. Frost Ridge minimum and maximum nivation-driven denudation rates. Rates based on

425 the middle- (25 ka) to late-Wisconsinan (11 ka) envelope for the deglaciation of Frost Ridge.

min. - max. Incipient Terraces -1 (cm ka ) 1 2 3 1 14.8 – 33.6 10.8 – 24.6 5.6 – 12.7 2 6.0 – 13.6 2.8 – 6.4 1.6 – 3.6 3 7.2 – 16.4 4.0 – 9.1 3.6 – 8.2 4 8.0 – 18.2 4.0 – 9.1 2.4 – 5.5 Marginal 5 9.2 – 20.9 7.2 – 16.4 4.8 – 10.9 Drainage Feature 6 6.4 – 14.6 3.2 – 7.3 2.0 – 4.6 426 Draft 427

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428 Figure Captions

429 Fig. 1. Map of Edgar Lake valley including the study area on the northerly aspect of Frost Ridge.

430 Perennial snow and ice fields are shown in white and place names are from Cialek (1977). Spatial

431 data include Shuttle Radar Topography Mission 30 m DEM and shapefiles for glacier extents and

432 countries are from Natural Earth public data domain. Maps were compiled in ArcGIS 10.7.1

433 software.

434 Fig. 2. Photos of late-lying snowbanks and related geomorphic features. (A) View upslope of

435 north-facing flank of Frost Ridge, showing nearby peaks, locations of subsequent panel photos of

436 a cryoplanation terrace, snowbank occupied incipient terraces, and marginal drainage, and

437 snowdrift cirque incised in Frost Ridge (Photo by C.W. Queen, July 2017). Photo and topographic

438 profiles are provided for (B) the cryoplanationDraft terrace cut into NE-facing flank of Splinter Peak;(C)

439 an incipient cryoplanation terrace occupied by a late-lying snowbank fueling nivation processes;

440 and (D) a largely unmodified marginal drainage feature on the lower reaches of Frost Ridge,

441 displaying a prominent reverse slope indicative of fluvial incision (Photos B and D were taken in

442 August 1976 and C in July 2017 by F.E. Nelson). Elevation data for topographic profiles were

443 generated by the UAV survey conducted as part of this work and graphs were compiled in Grapher

444 10 software.

445 Fig. 3. Idealized schematic of Edgar Lake valley. Idealized profile of the controlled natural

446 experiment in Edgar Lake valley, formed by a branch of the ancestral Hobo-Llewellyn glacier.

447 Dashed lines indicate glacier levels during progressive deglaciation. Notches created by marginal

448 drainage are shown on the south-facing (right) valley wall and low elevations on the north-facing

449 (left) valley wall. These have been enlarged into step-like hollows and terraces on the north-facing

450 wall by periglacial processes associated with late-lying snowbanks.

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451 Fig. 4. Photo of late-lying snowbanks on Frost Ridge and their temperature and density profiles in

452 July 25th-27th, 2017. For scale, the snowbank occupying incipient terrace 1 (IT1) was 250 m wide

453 and the snowbank in incipient terrace 2 (IT2) was 230 m wide. Snow pit numbers and their

454 locations in the larger snowbanks are shown in the photo by C.W. Queen, 24 July 2017. Graphs

455 were compiled using Grapher 10 software.

456 Fig. 5. Three-dimensional representations of (A) eroded volume estimate based on volumetric

457 comparison; (B) map showing the extent covered by the UAV survey (average 5.84 cm2 spatial

458 resolution), and hectare plots (25 cm2 resolution); and (C-K) marginal drainage and incipient

459 terrace features where all axis units are the same as those shown in plot C for marginal drainage 460 feature 1. Surface renderings were compiledDraft using Surfer 12 software. 461

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Draft

Map of Edgar Lake valley including the study area on the northerly aspect of Frost Ridge. Perennial snow and ice fields are shown in white and place names are from Cialek (1977). Spatial data include Shuttle Radar Topography Mission 30 m DEM and shapefiles for glacier extents and countries are from Natural Earth public data domain. Maps were compiled in ArcGIS 10.7.1 software.

156x133mm (300 x 300 DPI)

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Draft

Photos of late-lying snowbanks and related geomorphic features. (A) View upslope of north-facing flank of Frost Ridge, showing nearby peaks, locations of subsequent panel photos of a cryoplanation terrace, snowbank occupied incipient terraces, and marginal drainage, and snowdrift cirque incised in Frost Ridge (Photo by C.W. Queen, July 2017). Photo and topographic profiles are provided for (B) the cryoplanation terrace cut into NE-facing flank of Splinter Peak;(C) an incipient cryoplanation terrace occupied by a late- lying snowbank fueling nivation processes; and (D) a largely unmodified marginal drainage feature on the lower reaches of Frost Ridge, displaying a prominent reverse slope indicative of fluvial incision (Photos B and D were taken in August 1976 and C in July 2017 by F.E. Nelson). Elevation data for topographic profiles were generated by the UAV survey conducted as part of this work and graphs were compiled in Grapher 10 software.

220x146mm (300 x 300 DPI)

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Idealized schematic of Edgar Lake valley. Idealized profile of the controlled natural experiment in Edgar Lake valley, formed by a branch of the ancestral Hobo-Llewellyn glacier. Dashed lines indicate glacier levels during progressive deglaciation. Notches created by marginal drainage are shown on the south-facing (right) valley wall and low elevations on the north-facingDraft (left) valley wall. These have been enlarged into step-like hollows and terraces on the north-facing wall by periglacial processes associated with late-lying snowbanks.

194x103mm (300 x 300 DPI)

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Photo of late-lying snowbanks on Frost Ridge and their temperature and density profiles in July 25th-27th, 2017. For scale, the snowbank occupying incipient terrace 1 (IT1) was 250 m wide and the snowbank in incipient terrace 2 (IT2) was 230 m wide. Snow pit numbers and their locations in the larger snowbanks are shown in the photo by C.W. Queen, 24 JulyDraft 2017. Graphs were compiled using Grapher 10 software. 165x83mm (599 x 599 DPI)

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Draft

Three-dimensional representations of (A) eroded volume estimate based on volumetric comparison; (B) map showing the extent covered by the UAV survey (average 5.84 cm2 spatial resolution), and hectare plots (25 cm2 resolution); and (C-K) marginal drainage and incipient terrace features where all axis units are the same as those shown in plot C for marginal drainage feature 1. Surface renderings were compiled using Surfer 12 software.

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