Antarctica: The McMurdo Dry Valleys
Relative to most northern hemisphere glacial regions, the McMurdo Dry Valleys of Antarctica are slow to change. Very low precipitation and melt rates have allowed ice just below ground surface to survive for, in some cases, hundreds of thousands of years or more. Along with colleagues at UMass-Lowell, Brown University, and U Penn, I am studying the age, hydrology, and geochemistry of Dry Valleys buried ice. During the 2015 field season, we collected ice, sediment, and rock samples from Taylor, Pearse, and Wright Valleys.
1. Soil and salt along an Antarctic rock glacier
In the South Fork of Wright Valley, a 7-km long rock glacier stretches down to Don Juan Pond, an extremely hypersaline little lake of interest to planetary geologists. At the surface, the rock glacier is covered by talus from steep granitic and doleritic valley walls. I am analyzing the mineralogy of sediments composing the upper couple decimeters of the rock glacier. Is there a weathering trend along the rock glacier? Can we use the weathering products to estimate an age of the feature? To complement this work, I am performing leaching studies of the same sediments to identify salts and the potential contribution of major ions in the rock glacier to the meltwater that feeds Don Juan Pond.
2. Using a rock glacier to indirectly identify alpine glacier advances
In the Kukri Hills of East Antarctica, a portion of the Doran Glacier margin is bounded by a steep bedrock cliff. Ice falling down the cliff is incorporated into a small, rumpled rock glacier. While in the field, we noticed that the surface character of the rock glacier varies from fresh, unweathered boulders at the top, to grussified and ventifacted clasts near the toe. Analysis of the salinities of meltwater ponds scattered along the rock glacier suggest a similar story- the lower rock glacier is saltier and more weathered, and much older, than the upper rock glacier. Our work points to repeated advances of Doran Glacier (the source of rock glacier ice), which are recorded in the surface weathering and topography of this rock glacier. This highlights the potential utility of rock glaciers in this area to indirectly record alpine glacier advances, even when the direct evidence of those advances are unavailable.
3. Dating an advance of Rhone Glacier, Antarctica
Exiting from the Asgard Range into the well-studied Taylor Valley is the Rhone valley glacier. Rhone has a beautiful set of lateral moraines a couple hundred meters outboard of its modern, ice-cored moraines. These older lateral moraines extend nearly to the margin of Taylor Glacier, begging the question: Did Rhone Glacier advance at a time when Taylor Glacier was relatively retracted? I am using 3He cosmogenic surface exposure dating to develop a chronology of these moraines and place Rhone’s behavior into a regional paleoclimate and ice dynamics context.