Characteristics of surge‐type glaciers

Abstract

Glaciers can be divided into two classes according to their flow behavior: normal (relatively steady annually averaged flow rate) and surge-type (pronounced cyclic flow variations having a typical periodicity of 10-100 years). We have examined the population statistics of 2356 glaciers in the St. Elias Mountains, Yukon Territory, Canada, and estimate that 151 (6.4%) of these glaciers are surge-type. To explore how various glacier attributes are associated with surging, we compare the probability of surging associated with various subsets of the complete population to appropriate reference values. In this way, potential influences on surge tendency can be examined. For the 55 drainage basins analyzed, there is a pronounced spatial variation in the concentration of surge-type glaciers, but no obvious environmental control can be evinced. Within the study area the greatest concentration lies in the northern St. Elias Mountains, a region of high topographic elevation that is experiencing rapid tectonic uplift. Analysis of the influence of length on surge tendency reveals that long glaciers have a significantly greater probability of being surge-type than short glaciers. The surge probability increases monotonically from 0.61% for very short glaciers (0-1 km) to 65.1% for long glaciers (10-75 km). This result suggests that ice sheets and ice caps, or at least portions of them, should have a high probability of surging. Tributary glaciers have a greater tendency to surge than trunk glaciers, presumably because they may themselves be surge-type and may additionally participate in surges of the trunk glacier. The nonrandom geographical distribution of surge-type glaciers is not simply a consequence of the variation from basin to basin of the glacier length distribution. Surge-type glaciers tend to have a higher overall elevation than normal glaciers: the elevation of the highest point of the accumulation zone, the elevation of the snow line, and the elevation of the lowest point of the ablation zone, on average, exceed the corresponding elevations for normal glaciers. There is no significant difference between the overall slopes of surge-type and normal glaciers, although there is a tendency for surge-type glaciers to have greater slope in the accumulation zone and lesser slope in the ablation zone than normal glaciers. Although the prevalent flow direction for glaciers in the Yukon data set is to the north, surge-type glaciers tend to flow to the east and southeast. This orientation influence is probably explained by the fact that many of the longest glaciers also flow to the east and southeast. Papernumber 5B5680. 0148-0227/86/005 B 5680505.00 fled 204 surge-type glaciers in western North America, and all are located in the mountain ranges of Alaska, Yukon Territory, and northwestern British Columbia, the majority being s•tuated in the St. Elias Mountains near the Alaska Yukon border. No surging glaciers are found in ranges to the south such as the Coast Mountains, the Selkirk Mountains, and the Rocky Mountains. Other ...

Rock avalanches that travel onto glaciers and related developments, Karakoram Himalaya, Inner Asia

“…Existing models appear to refute the thesis that surges can be triggered by external events like landslides or earthquakes (Clarke et al, 1986;Kamb, 1987). Yet, it is difficult to believe they were purely coincidental.…”

Late nineteenth to early twenty-first century behavior of Alaskan glaciers as indicators of changing regional climate

“…About 75% of these were in Alaska. Clarke et al (1986) noted that only 6.4% (151 of 2356) glaciers they examined in the St. Elias Mountains of Canada were surge type.…”

Present dynamics and future prognosis of a slowly surging glacier

“…Based on aerial photographic evidence (from the National Air Photo Library, Ottawa, Ontario: Department of Energy Mines and Resources), we know the study glacier surged in 1951; by 1977 it had retreated over 1 km up-valley and was in a quiescent state (see De Paoli and Flowers, 2009). It surged again in 1986(P. Johnson, personal communication, 2006 and had all the visual hallmarks of a traditional surge at that time, including a heavily crevassed surface, shear margins near the valley walls, a thickening of the lower glacier and a steep and advancing ice front. Our observational program began in 2006 and included annual and summer measurements of glacier surface velocity at a stake network (Fig.…”

“…Variegated Glacier, Alaska, provides an example of a strong relationship between cumulative net balance and surge occurrence (Eisen et al, 2001). In addition to these requirements, substrate geology appears to be significantly correlated with the incidence of some surge-type glaciers (e.g., Clarke et al, 1984;Hamilton and Dowdeswell, 1996;Jiskoot et al, 2000) and may help explain the non-uniform geographical distribution of these glaciers (Post, 1969;Clarke et al, 1986).…”