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? : https://mc06.manuscriptcentral.com/cjes-pubs Page 1 of 28 Canadian Journal of Earth Sciences 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 1 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 2 of 28 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 2 https://mc06.manuscriptcentral.com/cjes-pubs Page 3 of 28 Canadian Journal of Earth Sciences 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 3 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 4 of 28 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 4 https://mc06.manuscriptcentral.com/cjes-pubs Page 5 of 28 Canadian Journal of Earth Sciences 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).