Cavernous Weathering in the Taylor Dry Valley, Victoria Land, Antarctica
TAYLOR VALLEY (77° 33′ S., 163° 25′ E.) is part of a deglaciated valley complex called the McMurdo Oasis, which is located about 80 km to the west of Ross Island across McMurdo Sound. Since the IGY many New Zealand and American geological parties have worked in this area1–3, which is easily accessible by helicopter from Scott Base and McMurdo Station at the southern end of Ross Island. Now that the topographical and geological reconnaissance stage has been completed and adequate maps cover the 2,500 km2 of the McMurdo Oasis, more attention is being devoted to the study of various anomalies and problems.
Universal Shapes? Analysis of the Shape of Antarctic Tafoni
Using dimensional data from over 700 tafoni in Antarctica, this paper identifies how the dimensionless ratios of width/length (W/L) and depth/length (D/L) vary with tafoni length. The analysis suggests that these ratios do tend to converge to values that are similar to those found for fragments produced by brittle fracture and fragmentation. Dividing the data into quintiles and deciles, it is possible to assess how tafoni size and shape change as tafoni length increases. Smaller tafoni do tend to have a rounder plan form which rapidly changes as tafoni length increases towards the W/L ratio of 0.67. It is suggested that initial tafoni development is limited by the conditions set out in a recent mathematical model of tafoni development. This model focuses on tafoni development through the interactions of variable rock strength and the varying concentration gradient of a corrosive agent. Erosion involves the removal of relatively small sections of rock and is analogous to a continuous erosional process. This model produces tafoni of relatively circular plan form. Above a certain tafoni length it is suggested that processes associated with brittle fracture begin to dominant the development and shape of tafoni.
The micro-mechanical behaviour of artificially cemented sand particles under compression and shear
The mechanical behaviour of cemented sands at macro-scale has been widely studied in the past, while there is still a lack of laboratory test data for the micro-mechanical response. Therefore, a series of uniaxial compression and tangential shear tests on artificially cemented sand particles have been conducted using a microscope to observe their behaviour. First, the consistency of cemented particles with different cementing agents is discussed. Three breakage modes are proposed according to the images taken using a microscope camera. A new parameter named ‘local roundness at contact’ is introduced to emphasise the effect of contact morphology on sample strength. Moreover, the effect of bond thickness on the mechanical response of cemented particles has been investigated. Finally, the shear strength parameters of artificially cemented sand samples have been determined for two different sample diameters.