Potential climatic refugia in semi-arid, temperate mountains: Plant and arthropod assemblages associated with rock glaciers, talus slopes, and their forefield wetlands, Sierra Nevada, California, USA

Abstract. Mountain permafrost and rock glaciers in the dry Andes are of growing interest due to the increase in human activities in this remote area. Empirical models of mountain permafrost distribution based on the spatial analysis of intact and relict rock glaciers and mean annual air temperature (MAAT) have been established as a tool for regional-scale assessments of permafrost favorability across entire mountain ranges; however, this kind of model approach has never been applied for a large portion of the Andes. In the present study, this methodology is applied to map permafrost favorability throughout the semi-arid Andes of central Chile (29° S–32° S), excluding areas of exposed bedrock. After spatially modeling MAAT distribution from scarce temperature records (116 station-years) using a linear mixed-effects model (LMEM), a generalized additive model (GAM) was built to model the activity status of 3524 rock glaciers. A Permafrost Favorability Index (PFI) was obtained by adjusting model predictions for conceptual differences between permafrost and rock glacier distribution. The results indicate that model has an acceptable performance (median AUROC: 0.76). Conditions highly favorable to permafrost presence (PFI ≥ 0.75) are predicted for 1051 km2 of mountain terrain, or 2.7 % of the total area of the watersheds studied. Favorable conditions are expected to occur in 2636 km2, or 6.8 % of the area. Especially in the Elqui and Huasco watersheds in the northern half of the study area, where a substantial surface portion (11.8 % each) was considered to be favorable for permafrost presence, while predicted favorable areas in the southern Limarí and Choapa watersheds are mostly limited to specific sub-watersheds. In the future, local ground-truth observations will be required to confirm permafrost presence in favorable areas, and to monitor permafrost evolution under the influence of climate change.

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Permafrost distribution modelling in the semi-arid Chilean Andes

The Cryosphere ◽

10.5194/tc-11-877-2017 ◽

2017 ◽

Vol 11 (2) ◽

pp. 877-890 ◽

Cited By ~ 33

Author(s):

Guillermo F. Azócar ◽

Alexander Brenning ◽

Xavier Bodin

Keyword(s):

Regional Scale ◽

Additive Model ◽

Mining Industry ◽

Ground Truth ◽

Infrastructure Development ◽

Rock Glacier ◽

Mountain Permafrost ◽

Rock Glaciers ◽

Temperature Records ◽

Semi Arid

Abstract. Mountain permafrost and rock glaciers in the dry Andes are of growing interest due to the increase in mining industry and infrastructure development in this remote area. Empirical models of mountain permafrost distribution based on rock glacier activity status and temperature data have been established as a tool for regional-scale assessments of its distribution; this kind of model approach has never been applied for a large portion of the Andes. In the present study, this methodology is applied to map permafrost favourability throughout the semi-arid Andes of central Chile (29–32° S), excluding areas of exposed bedrock. After spatially modelling of the mean annual air temperature distribution from scarce temperature records (116 station years) using a linear mixed-effects model, a generalized additive model was built to model the activity status of 3524 rock glaciers. A permafrost favourability index (PFI) was obtained by adjusting model predictions for conceptual differences between permafrost and rock glacier distribution. The results indicate that the model has an acceptable performance (median AUROC: 0.76). Conditions highly favourable to permafrost presence (PFI ≥  0.75) are predicted for 1051 km2 of mountain terrain, or 2.7 % of the total area of the watersheds studied. Favourable conditions are expected to occur in 2636 km2, or 6.8 % of the area. Substantial portions of the Elqui and Huasco watersheds are considered to be favourable for permafrost presence (11.8 % each), while in the Limarí and Choapa watersheds permafrost is expected to be mostly limited to specific sub-watersheds. In the future, local ground-truth observations will be required to confirm permafrost presence in favourable areas and to monitor permafrost evolution under the influence of climate change.

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Thermal and hydrologic attributes of rock glaciers and related landforms in the Sierra Nevada, California: Five years of iButton records

Quaternary International ◽

10.1016/j.quaint.2013.07.094 ◽

2013 ◽

Vol 310 ◽

pp. 237-238 ◽

Cited By ~ 1

Author(s):

Constance I. Millar ◽

Robert D. Westfall ◽

Diane L. Delany

Keyword(s):

Sierra Nevada ◽

Rock Glaciers

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Surface motion of active rock glaciers in the Sierra Nevada, California, USA: inventory and a case study using InSAR

The Cryosphere Discussions ◽

10.5194/tcd-7-343-2013 ◽

2013 ◽

Vol 7 (1) ◽

pp. 343-371 ◽

Cited By ~ 4

Author(s):

◽

C. I. Millar ◽

R. D. Westfall ◽

H. A. Zebker

Keyword(s):

Seasonal Variation ◽

Sierra Nevada ◽

Late Summer ◽

Mean Value ◽

Flow Speed ◽

Surface Flow ◽

Spatial Gradient ◽

Temporal Sampling ◽

Rock Glaciers

Abstract. Despite the abundance of rock glaciers in the Sierra Nevada of California, USA, few efforts have been made to measure their surface flow. Here we use the interferometric synthetic aperture radar (InSAR) technique to compile a~benchmark inventory describing the kinematic state of 59 active rock glaciers in this region. Statistically, these rock glaciers moved at speeds range from 15 cm yr−1 to 88 cm yr−1 with a mean value of 55 cm yr−1 in the late summer of 2007. We also find a spatial gradient: rock glaciers in the southern Sierra Nevada moved faster than the ones in the central Sierra Nevada. In addition to the inventory mapping, we also conduct a case study to measure the surface flow of the Mount Gibbs rock glacier in fine spatial and temporal detail. The InSAR measurements over this target reveal (1) that the spatial pattern of surface flow is influenced by surface geomorphological features and (2) a significant seasonal variation of flow speed whose peak value was 48 cm yr−1 in the fall, more than twice the minimum value observed in the spring. The seasonal variation lagged air temperatures by three months and likely results from temporal changes in mechanical strength of mixing debris and ice, internal melting of ice, and surface snow cover. Our finding on the seasonal variation of surface speed reinforces the importance of a long time series with high temporal sampling rates to detect possible long-term changes of rock glaciers in a warming climate.

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