Evolution of Channels on Taylor Glacier, Taylor Valley, Antarctica

Master's Thesis Work of Robin R. Johnston 

Department of Geology - Portland State University - Portland, Oregon

The National Science Foundation's (NSF) McMurdo Dry Valleys Long-Term Ecological Research (McMurdo LTER) project was established in Antarctica in 1992 to study the physical and biological constraints on the structure of ecosystems in the region. Andrew Fountain, with Portland State University, has been McMurdo LTER principle investigator responsible for studying the glaciers in the dry valleys.  The dry valleys (location) are one of the coldest and driest regions on the planet, and the ecosystems in the valleys rely primarily on the meltwater from glaciers in the valleys. The climatic conditions of this cold desert offer a rare opportunity to investigate the development and progression of supraglacial channels on a polar glacier.

These glaciers are thermally defined as "cold" glaciers - that is, their internal temperatures are below the pressure melting point - and they lack the conduit systems that transport water internally which are typically found on temperate, or "warm" glaciers. Therefore, meltwater derived from the glaciers in the dry valleys comes from the glacier surface. On the lower ablation zone of Taylor Glacier, deep-cutting channels have developed on that surface. One of the primary goals of my thesis research is determining the evolution of these channels by studying ablation in the lower reaches of the glacier through modeling of the energy balance in the region of the glacier where the channels occur.



  • Deeply incised channels on the lower ablation area of Taylor Glacier (lower left) are visible in this 1999 aerial photograph (courtesy Dennis Kenley). Taylor Glaciers enters Taylor Valley from the East Antarctic Ice Sheet (background left). Ice-covered Lake Bonney, the proglacial lake at the snout of Taylor Glacier, is visible in the foreground. Rhone Glacier enters Taylor Valley from the Asgard Range (center right).



    We believe that the morphology of these channels originates with changes in surface albedo caused by the deposition of rock material as medial moraines or wind-transported sand.  The development of the channels probably depend on the energy distribution across the channel surface. The following images depict the evolution of one of the channels down glacier...


    The following photo series illustrates the progression of one channel. (Photos courtesy Thomas Nylen)

    Cross-section 02

    Cross-section 03

    Cross-section 04

    Cross-section 05

    Cross-section 08

    Cross-section 09

    Cross-section 10

    Cross-section 11

    Cross-section 12

    Cross-section 13

    Cross-section 14



    Cryoconite holes may also play an important role in the development of the channel, as discussed by Karen Lewis in her forthcoming dissertation.  Cryoconite holes are cylindrical shaped holes in the glacier that begin to develop when wind-blown sand gets trapped in a slight depression on the glacier surface. This sand has a lower albedo than the surrounding ice and absorbs solar radiation differentially, thus melting in the glacier surface. The sediment continues melting into the ice, roughly normal to the glacier surface, until solar radiation can no longer reach it directly. 

    • Schematic of the cross-section profile of a cryoconite hole.



    Sediment is then trapped in the base of the cryoconite hole and is covered by a column of liquid water. Over time an ice cap develops at the top of the cryoconite hole.


    • Cryoconite holes as they appear on the glacier surface, ranging in size from a few cm to roughly 50 cm in this image.

    • As the widening of the channel progresses the cyroconite holes near the channel wall become cannibalized, the sediment and water within them is flushed to the channel wall and floor. This acts as a positive feedback mechanism that enhances melt.

    • The effects of this cannibalization can be dramatic. This is an image looking across the channel to the south, rather than down-glacier. Note person for scale. Click for a larger image. (Photo courtesy Thomas Nylen)


    I am in the process of developing a model of channel enlargement with distance down glacier. More on this later...



    This web site is a work in progress and I will be updating it from time to time. Please feel free to contact me at robj@pdx.edu with questions or comments.