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Home , Rock glacier, Scree, Solifluction

AND PERIGLACIAL ROCK-ICE FEATURES IN THE EASTERN SIERRA NEVADA; UPDATES ON CLASSIFICATION, MAPPING, RELATIONS, AND MONITORING CONSTANCE MILLAR 1, DAVID CLOW 2, JESSICA LUNDQUIST 3, AND ROBERT WESTFALL 1

1 USDA Forest Service, Sierra Nevada Research Center, Berkeley, CA 2 USGS, Water Resources Division, Denver, CO 3 NOAA, Earth Systems Laboratory, Boulder, CO

BACKGROUND Rock glaciers and related periglacial rock-ice (R-I) features are common but little-studied landforms in high mountains where conditions are relatively dry and adequate sources of shattered rock exist. While many of these features in temperate mountains appear to be relicts, a large proportion shows indications of activity, suggesting persistent embedded or underlying ice. Recent retreat of “clean glaciers” worldwide has been related to global warming. Rock-mantling and rock matrices, however, insulate rock glaciers and R-I features, and their activity and equilibrium with climate appear to considerably lag clean glaciers. They remain potentially important mountain reservoirs, yet overlooked in hydrologic research. For this and other reasons, research attention to the distribution, activity, genesis, and hydrology of rock glaciers has increased in recent years. Debate on the glaciogenic vs. periglacial () origins of these features (Clark et al. 1998) has been confounded by inconsistent terms and definitions, lack of a sufficient classification, and by the varying expression of processes that occur under climatic and environmental conditions in different regions. Rock glaciers and R-I features are abundant in and canyons of the Sierra Nevada south of Lake Tahoe, especially along the eastern escarpment, where they occur in diverse forms (Figs. 1 & 2). Several large rock glaciers have been studied for their climatic and neo-glacial relationships (Clark, pers. comm.; Konrad & Clark 1998), and a few Pleistocene relict rock glaciers are indicated on high-resolution geologic maps of the Sierra. These features are mentioned in passing in Sierran scientific and popular natural-history literature, but aside from Clark and his students’ research, no systematic studies have been published. While several papers from Europe and North America describe types of rock glaciers, define terms, and offer classifications, none proved sufficient to identify and map the range of features in the Sierra Nevada. We undertook work described here in hope that field-based mapping and a field- friendly taxonomy will assist future mapping, for example, from aerial photography. With the reconnaissance-level monitoring we are beginning, we further hope to encourage glacial, hydrologic, and ecologic research on these landforms. We include a wider range of features in our classification than is usually discussed to highlight potential physical interrelationships of these features and possible hydrologic significance of overlooked forms.

GOALS: Relative to rock glaciers and associated periglacial R-I features of the Sierra Nevada: • Develop a taxonomic classification and nomenclature • Compile maps and geo-referenced databases derived from field-mapping • Analyze geographic and climatic relations of the features • Form tentative hypotheses of process and origins • Initiate reconnaissance monitoring of rock and R-I feature 1) movement, 2) meltwater, including flow, seasonal persistence, temperature, and chemistry and 3) and plant cover and ages.

METHODS Fig 1. Goethe Fig 2. Rock Glacier near Taboose Pass Mapping and Classification During field seasons of 2000-2005, Millar mapped discrete R-I features whose location and morphology suggested glacial or periglacial origins – e.g., rock glaciers, active , protalus ramparts, slumps, patterned-ground circles, nets, stripes, and intermediate features. Conventional clean glaciers and persistent snowfields without associated decomposed rock mantling were not included. Each feature was field-mapped at coarse resolution on topographic maps and later characterized with digital maps (TOPO!) for latitude and longitude (center of feature), elevation range, and local aspect. Feature size was described in four ranks (400 ha, 50ha, 5 ha, 0.5 ha); three shape ranks were scored (wider than long, ~equal length & width, longer than wide). Current activity (embedded ice) is difficult to determine by casual observation. A feature was tentatively scored Active if it was: 1) within the elevation range of clean glaciers and persistent snowfields; and had 2) oversteepened front and sides (rock glacier types only); 3) angular rocks with no or little lichen growth; 4) plant cover absent or minimal; and 5) persistent spring or stream or presence of phreatophytes (e.g., willows, rushes) at the feature’s toe. Based on observations of ~300 features, a preliminary taxonomy and nomenclature were developed. This was tested by revisits to ~20% of the originally mapped features, and addition of ~100 new features, which led to the revised classification presented here. Climate Location data for all R-I features were imported into GIS as point coverages (lat/long of centers). These were intersected with 4km2 gridded data from the PRISM climate model (Daly et al., 1994), and adjusted to site-specific elevations using lapse rates from PRISM. We extracted layers for annual, January, and July minimum and maximum temperatures, respectively, and annual, January, and July , respectively, for the period of record, 1960-1999. The PRISM grids were converted to polygons and sequentially intersected with the locations of the R-I features, grouped by the six Location Classes (see Results). GIS analyses were done in ARC/Info. To determine differences among Location Classes, we subjected the merged R-I-feature/PRISM-climate data to discriminant analysis. We classified the analysis by Location Class with the climatic measures as variables, maximizing R-I-feature differences in multivariate climate space. We then computed mean climatic data from the PRISM model for the classified groups.

Monitoring Reconnaissance monitoring was initiated in summer, 2005 (Table 1). We report preliminary results for water chemistry only; other elements await downloading and/or first measurements in summer 2006. Water Chemistry. On Oct 24-25, 2005, we sampled water from springs and streams emanating at the bases of six R-I features for chemical analysis. Water sampling and analytic methods followed Clow et al., 2002. To assess differences among sites, we used principal component analysis (PCA), with ln-transformed data to normalize the distribution. We used PCA and discriminant analysis on ln- transformed data to resolve clusters and then test differences of the rock-ice meltwater chemistry data to values previously analyzed from precipitation (6 samples, 2003-04), snow (2 samples, 2005), river (123 samples, 2003-05), and lake (15 samples, 2003-05) sources (Clow et al., 2002). Water Temperature and Depth. Water temperature is being recorded by ten small dataloggers (iButtons), programmed for four readings/day and seven larger level-loggers (solinsts), programmed to read every half hour. We placed all instruments in shallow pools (15-30 cm) at the spring heads or where meltwater streams first surfaced from R-I features (Figs. 3 and 4). Readings will give indications of temperature persistence and variability, timing in change of state from liquid to frozen, and timing of spring/stream drying, if any – all of which will help interpret the internal hydrologic structure of the features. Leveloggers also record water pressure, which, together with barometric pressure measured from barologgers installed at Tuolumne Meadows, Yosemite NP (2600 m; Lundquist, ongoing research), will enable calculation of water depth. Rock-Ice Feature Movement. We installed rudimentary transects to monitor movement of boulders on the steep front of one rock glacier (RGV, see Results), upper surfaces of two other rock glaciers (RGC), and across the bases of three boulder streams (BSC). Paint spots were sprayed on boulders every 1.7 m along an azimuth perpendicular to the inferred flow direction, with base-points on bedrock off the edge of the R-I features. Transects will be re-visited to determine if paint spots moved.

Fig 3. Spring, Kidney Lk Boulder Stream Fig 4. Stream surfacing, Kuna Crest Rock Glacier RESULTS & DISCUSSION Classification and Mapping From field surveys, 395 R-I features were mapped (Appendix 1). A taxonomic classification, in which geomorphic relationships are inferred by taxonomic relationship, is proposed (Table 2). The classification describes three hierarchic levels: 4 Condition States, 6 Location Classes, and 18 Position Types. Condition States are the major categories of R-I features; Location Classes describe the location of features within the Condition State; and Position Types are the terminal categories. Type localities for each of the Position Types are identified, and a subset is illustrated (Figs 5-12). The classification is based on morphology and location, does not rely on inference of glacial vs. periglacial origins, and is intended for easy field use.

Fig 5. RGC-V, Mt. Gibbs Fig 6. RGC-M, Mt. Kuna

Fig 13. Slope aspects for Location Classes

Summary of Main Groups Geographic location, size, and shape means for the Condition States and Location Classes are given in Table 3, and aspects are indicated by wind rose diagrams for the Location Classes in Fig. 13. Rock Glaciers/Periglaciers: Simple or complexly lobed, discrete landforms of shattered and sorted rock; till reversely sorted (fines low; coarse high); fronts and sides are oversteepened and tops are overflattened relative to the ambient or valley slope. Ice is rarely visible except in occasional meltponds (karst ponds) where massive, laminated ice bodies may underlie the rock mantle, or in persistent snow/icefields adhering to cirque or walls above the rock feature. Running water often heard Fig 7. RGV-Sc, East Fork Rock Cr. Fig 8. RGV-C, Francis Cyn. far below the rock surface. Features may originate in high cirques and either remain within the cirque confines or emanate downvalley with fronts perpendicular to the valley axis. Clean glacier terminal moraines may become active Rock Glaciers. Other features occur on valley walls, in the middle of slopes, in talus cones, or beneath cliffs or avalanche shoots, and their fronts parallel the valley axis. Potential Origins: Glacial (rock mantling on clean glaciers) or periglacial (transiently persistent ice interacting with shattered rock masses). Potentially interchangeable as change. Boulder Streams: Landforms similar to Rock Glacier/Rock Periglaciers dominated by sorted, shattered rock, but lacking oversteepened fronts or sides. Boulder Stream front boundaries occur where large sorted boulders abruptly meet deep, wet, organic soils supporting mesic “turf” vegetation that appears to be rolling (carpet like) over the landform front. Running water often heard far below the rock surface. Boulder Streams occur on scree slopes in similar topographic locations as Rock Glaciers/Periglaciers but in addition may occur below snowfields on gentle slopes, or along streamcourses in valley bottoms or Fig 9. BSC-Sc, Helen Lk. Fig 10. BSC-Sa, Mt. Dunderberg slopes. Potential Origins: Periglacial. : Similar to Boulder Streams but not appearing to be associated with running water. Small units of distinctly bounded, sorted rock abruptly adjacent to weathered soil surfaces. Round circles are on very high, exposed, often snow-free plateaus, benches and slopes; other features bound alpine lake margins. Potential Origins: Periglacial (permafrost and/or seasonally frozen ground processes, e.g., freeze-thaw, convection, contraction) : Typical solifluction features form on very high exposed alpine slopes and are complexly hummocked with reversely sorted structure in each hummock. Individual hummocks may have oversteepened fronts relative to the general slope, but are not as abrupt as in Rock Glaciers/Periglaciers. More soil may be developed on these features than other groups described. Potential Origins: Periglacial (downslope movement of saturated soils interacting with permanently and/or transiently frozen Fig 11. PGA-L, East Fork Rock Cr. Fig 12. MWA-S, Mt. Olsen ground)

Climate Modeling Table 4 shows mean climate values from the PRISM model for active R-I features east of the Sierra crest (n=294 of 395 total), grouped by the six Location Classes in Table 3. Of special interest are the mean annual air temperatures (MAAT); conditions for persistent permafrost require ≤ 0°C. The coldest R-I features are the solufluction fields (MWA-S) and cirque rock glaciers (RGC), whose MAAT are estimated from PRISM as < 1°C. These means are maximum value estimates because they are adjusted from the average PRISM tile only for elevation and not for aspect. Thus, several of the R-I categories may have MAAT ≤ 0°C, as has been calculated for the nearby White Mtns. The first three canonical vectors explained 91% of the variation; canonical analysis indicated annual, January, and July maximum temperatures to be important variables distinguishing the six R-I Location Classes. Water Chemistry A PCA on chemical concentrations (Table 5.) of the six rock-ice meltwater streams yielded two principal components, both of which separated the three Mammoth Crest sites from the three Bridgeport sites. Na, SO4, Cl, and Mg were correlated with the 1st PCA; NO3, H, and Ca (negative) were correlated with the 2nd PC. Substrate differences between the two sites (Mammoth, granitic; Bridgeport, diverse metavolcanics) and associated effects are a possible explanation of differences, although air masses over the Mammoth sites may derive from more polluted southern California regions distinct from those that reach the Bridgeport sites, and may contribute to differences in chemistry of precipitation. PCA resolved five clusters of data: precipitation, snow, river, lake, and R-I meltwater. Discriminant analysis (DA) yielded two significant canonical vectors (CV). The 1st CV accounted for 84% of the variation; the 2nd CV for 7%. On CV1, precipitation and snow clustered toward one extreme from all other groups and the R-I sites clustered distinctly from all other groups at another extreme (Fig. 14). This suggests that the R-I water is more processed than the lake and river sites relative to incoming snow and precipitation. Combined, the chemistry results tentatively indicate for R-I features cold environments, where ice persists for years or decades; movement, whereby weathering of substrate generates new elements; and ice-inhabiting bacteria or other microbes, which may contribute metabolic products to meltwater (Mader et al., 2006).

Fig 14. Canonical-vector analysis plot of chemistry data from Sierran snow, precipitation, river, lake, and rock-ice feature water samples FUTURE WORK REFERENCES Plans for 2006 include recovery and downloading of water temperature and depth dataloggers and Clark, D.H., Steig, E.J., Potter, N., Gillespie, A.R. 1998. Geografiska Annaler 80 A: 3-4. remeasurement of line transects for movement. In addition, we will install 30 new temperature Clow, D.W., Striegl, R.G., Nanus, L., Mast, M.A., Campbell, D.H., Krabbenhoft, D.P. 2002. loggers in meltwater of a variety of R:I features and in nearby free air environments. We also plan to Water, Air, and Soil Pollution: Focus 2: 139-164. sample additional meltwater sources for water chemistry and to assess water age. In collaboration Daly, C., Neilson, R.P., Phillips, D.L., 1994. Journal of Applied Meteorology 33, 140-158. with R. Franklin (Univ. Arizona), we hope to begin surveys on rock glaciers of lichen and vascular Konrad, S., Clark, D.H., 1998. and Alpine Research 30, 272-284. plant cover and age as a means of evaluating rock-glacier activity. The classification and climate Mader, H.M., Pettitt, M.E., Wadham, J.L., Wolff, E.W., Parkes, R.J. 2006. Geology 34: 169-172. results are being prepared for publication (Millar and Westfall, in prep). Millar, C.I., Westfall, R.D. In prep. A.A.A.R.