Long‐runout rockslide on glacier at Tsar Mountain, Canadian Rocky Mountains: potential triggers, seismic and glaciological implications

Abstract

A rhomboidal shaped rockslide with a length of 2·2 km and an area of 1·35 km 2 covers 30% of a small Clemenceau Icefi eld Group cirque glacier. By means of remote sensing, airborne photography, climate and seismic data analysis, the extent, timing, possible trigger mechanisms, and rockslide effects on the glacier are discussed. An ML 2·0 seismic event on 14 September 2000 represents the rockslide and has a spindle-shaped waveform and high energy in the low frequencies. Based on a strong signal duration of 56-108 seconds the rockslide had an average runout velocity of 22-45 m s −1 . Stress fatigue and a combination of rain and snow followed by rapid melt and night-time freezing could have co-triggered the slide. Additional seismic events with epicentres <40 km from the cirque were recorded 26 times since 1985 and range between ML 0·9-3·3, but none were caused by, or triggered, large mass movement.With a rock source volume of 1·6 × 10 6 m 3 and a deposited volume of 2-4 × 10 6 m 3 the sum of bulking and entrainment is between 25% and 150%. Five melt seasons post-event, levees 20-30 m wide tower 30 m over the surrounding glacier. Rockslide characteristics, and its Fahrböschung of 15° [height/length (H/L) = 0·28], indicate that this rockslide is quite typical for long-runout rockslides on glaciers. However, the basal friction coeffi cient was higher than found on other glaciers and could relate to the presence of medial moraines transverse to the fl owline and to pre-slide debris-cover. The difference between the coeffi cient of friction in the main fl owline (0·11-0·14) and that in a lobe confi ned between two medial moraines (0·065) suggests that confi nement increases mobility by 70-115%. Apart from reduced ablation under the rock debris, effects of the rockslide on the glacier were minimal.

Using Stereo Satellite Imagery to Account for Ablation, Entrainment, and Compaction in Volume Calculations for Rock Avalanches on Glaciers: Application to the 2016 Lamplugh Rock Avalanche in Glacier Bay National Park, Alaska

“…Although the difference between the amounts of mobilized and accumulated material is within our error estimates, the increase in average volume between displacement and deposition is likely a result of (1) bulking from disintegration and fragmentation of source rock and (2) entrainment of substrate along the travel path (e.g., Hungr & Evans, ). Previous work suggests that the process of rock fragmentation alone can result in source volume expansion ranging from 15 to 25% (Jiskoot, ), while bulking values upward of 50% (Deline, ) are expected if substrate is entrained during emplacement. It is difficult to differentiate or quantify the bulking processes that occurred during emplacement of the Lamplugh rock avalanche without knowledge of the physical properties and relative amounts of rock and ice in the source and deposit material.…”

“…Figure a shows the elevation of the ice surface on 15 June 2016, which is lowered by (1) ablation of snow and ice on the glacier surface prior to the rock avalanche (Figure b) and (2) erosion of material at the basal surface of the rock avalanche during emplacement due to either scour and plowing of snow and ice (Delaney & Evans, ) or ablation from the generation of frictional heat (Pudasaini & Krautblatter, ; Sosio et al, ; Figure c). After the rock avalanche was emplaced, ablation of the surrounding ice continued while the rock avalanche debris insulated the underlying ice (e.g., Jiskoot, ; McSaveney, ; Reznichenko et al, ), causing the deposit to be elevated above the surrounding surface (Figure d). A reduced amount of ablation below the rock avalanche deposit and ablation of entrained snow and ice or compaction within the deposit additionally caused a decrease in the elevation of the deposit surface between rock avalanche emplacement and the acquisition of postevent data (Figure e).…”

“…Journal of Geophysical Research: Earth Surface Evans, 2004). Previous work suggests that the process of rock fragmentation alone can result in source volume expansion ranging from 15 to 25% (Jiskoot, 2011), while bulking values upward of 50% (Deline, 2009) are expected if substrate is entrained during emplacement. It is difficult to differentiate or quantify the bulking processes that occurred during emplacement of the Lamplugh rock avalanche without knowledge of the physical properties and relative amounts of rock and ice in the source and deposit material.…”

Landslide Amplification by Liquefaction of Runout‐Path Material after the 2008 Wenchuan (M 8·0) Earthquake, China

“…Dufresne et al, 2010;Jiskoot, 2011;Schneider et al, 2011). Dufresne et al, 2010;Jiskoot, 2011;Schneider et al, 2011).…”

Unraveling driving factors for large rock–ice avalanche mobility

“…(); [30] Huggel et al (); [31] Huggel et al . (); [32] Evans and Clague (); [33] Delaney and Evans (); [34] Jiskoot (); [35] Lipovsky et al . (); [36] http://daveslandslideblog.blogspot.com/search?q=meager; [37] Crandell and Fahnestock (); [38] Sheridan et al .…”