Canadian Journal of Earth Sciences
Long-Term Nivation Rates, Cathedral Massif, Northwestern British Columbia
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, Cryoplanation, UAV Survey, Keyword: Volumetric Erosion 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 patterned ground and
65 solifluction 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 ice segregation (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 permafrost (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 palsas 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 Cathedral Peak 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 cirque 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 cirques 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 Juneau Icefield 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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379 Nelson, F.E. 1998. Cryoplanation terrace orientation in Alaska. Geografiska Annaler: Series A,
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. Biuletyn Peryglacjalny, 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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