Supraglacial debris cover: global distribution, evolution and regional-scale effect on melt

• Main Author: Herreid, Samuel J.
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: F800 Physical and Terrestrial Geographical and Environmental Sciences; Greenland; New Zealand; Antarc*; Antarctica; glacier; glaciers; Alaska
• Online Access: https://nrl.northumbria.ac.uk/id/eprint/48715/; https://nrl.northumbria.ac.uk/id/eprint/48715/1/herreid.samuel_phd_150311851.pdf

Rock debris on the surface of glaciers form unique structures that evolve with a changing climate and have a net system impact that is unknown at wide scales. While a growing canon of literature is focused on single glaciers or sample regions well-suited to investigate supraglacial debris cover, a knowledge gap remains for the rest of Earth’s glaciers. A global inventory of debris cover was produced using the Randolph Glacier Inventory (RGI) and a set of manually selected Landsat images (n=271) showing that 6.0% of Earth’s mountain glaciers (excluding Greenland and Antarctica) are covered by rock debris. Debris-covered area was defined using a simple spectral band ratio threshold separating optically dark rock debris from optically light ice and snow. To improve the quality of this debris map, and to align mapped debris cover and glacier outlines in time,the RGI was adjusted to match the glacier extent expressed in the set of Landsat images. 2.4% of the RGI (version 6.0) was identified to be falsely classified as glacier area and an area equal to 0.3% of the RGI was identified as area falsely excluded from the inventory. Regional results show that the three most debris abundant regions on Earth, Alaska (11,287 km2), the Himalaya (8,759 km2) and Greenland (3,492 km2) make up 80% of Earth’s supraglacial debris cover (29,248 km2). Broken down further to an individual glacier scale, three new metrics were derived that summarize the state of each glacier’s debris cover. These metrics quantify the stage of a glacier between zero and complete debris coverage within the ablation zone and characterize the configuration of the glacier’s moraine structure and its ability to expand spatially. These metrics enable the placement of each glacier onto a conceptual timeline of debris cover evolution spanning 100s to 1,000s of years. The most advanced stage glaciers present on Earth today are concentrated in the Himalaya, Alaska and New Zealand. Direct measurements to help refine the thermal signal of debris cover in thermal ...