Ice cliff morphology and evolution on the Kennicott Glacier, Wrangell Mountains, Alaska.

Abstract:

The Kennicott Glacier is a large compound valley glacier flowing southward from its origins on the flanks of Mount Blackburn in the Wrangell Mountains, Alaska. Its lower reaches are continuously covered in debris, punctuated by a significant population of ice cliffs. These ice cliffs are important as melt hotspots that may counter the melt-reducing effect of a sufficiently thick surface debris layer.

Many ice cliffs on the Kennicott are undercut by supraglacial streams or border supraglacial ponds, an association which has likewise been observed on debris-covered glaciers in high mountain Asia. The degree to which hydrologic processes control the formation, evolution, and persistence of ice cliffs is not fully understood.

We plan to contribute to this understanding by (1) characterizing ice cliff morphology across the surface of the Kennicott and (2) detailed monitoring of the back-wasting and evolution of a single ice cliff, undercut by a minor supraglacial stream, throughout the 2020 melt season as imaged by a time lapse camera installation.

In this study we will use manual mapping in tandem with automated detection methods to extract ice cliffs from a high-resolution Structure-from-Motion DEM. Statistics are extracted for slope, slope aspect, and ice cliff size, as well as association with supraglacial streams and ponds.

From June – September 2020 we installed a time lapse camera trained on a ~10 m tall ice cliff with a slope of ~54 degrees undercut by a minor supraglacial ice stream. An ablation stake was installed horizontally into the cliff to enable quantitative estimates of cliff back wasting and stream incision. Preliminary results for the period June 15-19 show an average back wasting rate of ~8.9 cm / day at the cliff base.

We also installed a nearby Automatic Weather Station on the debris-covered ice to measure air temperature, 3D wind speed/direction, and four-component radiation as inputs for an energy balance model of debris-covered and exposed cliff ice.