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.