Search

Using in situ field measurements, laboratory analyses, and numerical modeling, we test the potential efficacy of thermal stress weathering in the flaking of millimeter‐thick alteration rinds observed on cobbles and boulders of Ferrar Dolerite on Mullins Glacier, McMurdo Dry Valleys (MDV). In particular, we examine whether low‐magnitude stresses, arising from temperature variations over time, result in thermal fatigue weathering, yielding slow crack propagation along existing cracks and ultimate flake detachment. Our field results show that during summer months clasts of Ferrar Dolerite experience large‐temperature gradients across partially detached alteration rinds (>4.7°C mm−1) and abrupt fluctuations in surface temperature (up to 12°C min−1); the latter are likely due to the combined effects of changing solar irradiation and cooling from episodic winds. The results of our thermal stress model, coupled with subcritical crack growth theory, suggest that thermal stresses induced at the base of thin alteration rinds ~2 mm thick, common on rocks exposed for ~105years, may be sufficient to cause existing cracks to propagate under present‐day meteorological forcing, eventually leading to rind detachment. The increase in porosity observed within alteration rinds relative to unaltered rock interiors, as well as predicted decreases in rind strength based on allied weathering studies, likely facilitates thermal stress crack propagation through a reduction of fracture toughness. We conclude that thermal stress weathering may be an active, though undervalued, weathering process in hyperarid, terrestrial polar deserts such as the stable upland region of the MDV. Antarctic dolerite clasts experience large temperature gradients and fast fluctuations in surface temperatureThermal fatigue weathering likely contributes to the spalling and flaking of dolerite boulders in AntarcticaAlteration rinds on dolerite clasts allow for local weakening and subcritical crack propagation under thermal stress

The Dry Valleys are subdivided into three microclimate zones on the basis of summertime measurements of atmospheric temperature, soil moisture, relative humidity and wind-speed/ direction. Subtle variations in these climate parameters result in considerable differences in process geomorphology and in the development of unique landforms within each zone. The mapped zones include a coastal thaw zone, an inland mixed zone and a stable upland zone. Landforms within each zone are subdivided into macroscale features (e.g. valleys, slopes and gullies), mesoscale features (e.g. polygons and viscous-flow features) and microscale features (e.g. rock and near-surface soil features, including the effects of salt weathering, wind erosion and pitting). We present a review of landscape development in the Dry Valleys with implications for long-term climate change and ice-sheet stability. Chronological control is afforded by 40Ar/39Ar dating of volcanic ash-fall deposits and cosmogenic nuclide analyses of surface boulders. Collectively, the data call for persistent cold and dry conditions in the stable upland zone for approximately the last 14 Ma, although some level of climatic amelioration and landform modification may have occurred within low-lying regions and in the inland mixed zone.

We present our experiences with the conjunctival approach for treatment of “blowout” fractures of the orbital floor. We recommend it.