Understanding controls on cirque floor altitudes: Insights from Kamchatka

Abstract

Glacial cirques reflect former regions of glacier initiation, and are therefore used as indicators of past climate. One specific way in which palaeoclimatic information is obtained from cirques is by analysing their elevations, on the assumption that cirque floor altitudes are a proxy for climatically controlled equilibrium-line altitudes (ELAs) during former periods of small scale (cirque-type) glaciation. However, specific controls on cirque altitudes are rarely assessed, and the validity of using cirque floor altitudes as a source of palaeoclimatic information remains open to question. In order to address this, here we analyse the distribution of 3520 ice-free cirques on the Kamchatka Peninsula (eastern Russia), and assess various controls on their floor altitudes. In addition, we analyse controls on the mid-altitudes of 503 modern glaciers, currently identifiable on the peninsula, and make comparisons with the cirque altitude data. The main study findings are that cirque floor altitudes increase steeply inland from the Pacific, suggesting that moisture availability (i.e., proximity to the coastline) played a key role in regulating the altitudes at which former (cirque-forming) glaciers were able to initiate. Other factors, such as latitude, aspect, topography, geology and neo-tectonics seem to have played a limited (but not insignificant) role in regulating cirque floor altitudes, though southfacing cirques are typically higher than their north-facing equivalents, potentially reflecting the impact of prevailing wind directions (from the SSE) and/or variations in solar radiation on the altitudes at A C C E P T E D M A N U S C R I P TACCEPTED MANUSCRIPT 2 which former glaciers were able to initiate. Trends in glacier and cirque altitudes across the peninsula are typically comparable (i.e., values typically rise from both the north and south, inland from the Pacific coastline, and where glaciers/cirques are south-facing), yet the relationship with latitude is stronger for modern glaciers, and the relationship with distance to the coastline (and to a lesser degree with aspect) is notably weaker. These differences suggest that former glacier initiation (leading to cirque formation) was largely regulated by moisture availability (during winter months) and the control this exerted on accumulation; whilst the survival of modern glaciers is also strongly regulated by the variety of climatic and non climatic factors that control ablation. As a result, relationships between modern glacier mid-altitudes and peninsula-wide climatic trends are more difficult to identify than when cirque floor altitudes are considered (i.e., cirque-forming glaciers were likely in climatic equilibrium, whereas modern glaciers may not be).

Spatial analysis of cirques from three regions of Iceland: implications for cirque formation and palaeoclimate

“…Most cirques in the Northern Hemisphere have a north or northeast aspect, similar to cirques in Iceland (Table 4). In a direct comparison with cirques studied in Kamchatka, Russia, by Barr & Spagnolo (2013, 2015b, ratios between L, W and H in Iceland exhibit similar patterns.…”

“…; Avdeiko et al . ; Barr & Spagnolo ), which would presumably exhibit characteristics similar to the Upper Tertiary basalts in Iceland. However, cirques in Iceland are much more circular and smaller than those on Kamchatka, Russia.…”

“…We used three techniques to reconstruct palaeo‐ELAs for Tröllaskagi and the East Fjords: the cirque‐floor (CF) method, the altitude‐ratio (THAR) method (summarized in Porter ) and the minimum‐point (MP) technique (summarized in Barr & Spagnolo ). Principato & Lee () calculated palaeo‐ELAs for Vestfirðir using the THAR and CF methods.…”

“…; Barr & Spagnolo , , b). Quantifying cirque morphology provides information about the distribution of cirques and processes impacting cirque formation (Evans ; Barr & Spagnolo , , b). Palaeoclimate records are commonly interpreted from cirque equilibrium‐line altitudes (ELAs), the elevation at which annual accumulation of snow equals annual ablation (e.g.…”

“…Previous studies show that distance to moisture sources and proximity to the ocean influence the elevation of palaeo‐ELAs (e.g. Benn & Evans Principato & Lee ; Barr & Spagnolo , , b). The purpose of our study is to add to these global data sets by providing a regional analysis of ice‐free cirques from three regions of Iceland.…”