||Dynamics of surge-type glaciers in Yukon, Canada, revealed by multi-satellite images
Surge-type glaciers repeatedly oscillate between a short active phase characterized by order-of-magnitude speed-up and a long quiescent phase. During the active phase, a significantlylarge volume of ice is transporteddownstream, causing surface elevation changes and terminus advance, as well as forming heavily-damaged crevasses and looped moraines. On the other hands, in the quiescent phase, they flows lowly or become stagnant in the downstream area, leading to ice thickeningin the reservoir area. The imbalanced flow results in retreat and thinning in the receiving area. Surge-type glaciers are distributed in specific areas, and one of highly concentrated zones is near the border of Alaska and Yukon, Canada. In this area, glacier surge often initiates in winter, but the triggering mechanism remains unclear. An extensive ground-based observation on the 1982-83 Variegated Glacier’s surge has brought a fundamental idea of surge generation mechanism. However, there remainsa question as to how basal water pressure increase and subsequent speed-up can be maintained without further input of meltwater from the surface. Moreover, it remains uncertain what controls the surge cycle, and generates the pre-condition before surging. To answer these questions, we used multi-satellite images to reveal dynamics of surge-type glaciers in Yukon, Canada. The detailed spatial and temporal changes in ice speed cantell us new insight into behaviors of surge-type glaciers during both quiescent and active phases. Surface elevation change data can show the place where surge initiates and how the surge front propagates downstream. Spatial patterns of looped moraines can reveal how the tributaries affects the trunk before and during surge.This thesis includes the following four topics; 1) Winter speed-up of quiescent surge-type glaciers in Yukon, Canada;2) Basal condition in winter using numerical glacier hydrological model;3) Twelve-year cyclic surging episodes at Donjek Glacier in Yukon, Canada;4) Surge dynamics ofSteele Glacier in Yukon, Canada, revealed by multi-satellite images. All these results have significant implications for better understanding the dynamics of not only surge-type glaciers but also glaciers and ice sheets in general.
Hokkaido University（北海道大学）. 博士(理学)