Malin Antarctic Images #1

- Photographed 1/15/94 by M. Malin

Sorted polygon in glacial debris covering floor of Bull Pass in Southern Victoria Land, Antarctica. Located at 77 deg 26.7 min S 161 deg 40.2 min E, at an altitude of 730 m (2460 ft). Both coarse and fine-grained materials can be found in polygonal depressions, and both raised and depressed centers can occur. These polygons have coarse, raised centers, coarse marginal trenches, and coarse-depleted, gently sloping shoulders. Sorted polygons are among a number of enigmatic landforms developed in periglacial environments. A leading explanation for these types of sorted polygons is that the upper regolith in periglacial environments convects, or experiences diapirism, driven either by temperature or density gradients.

- Photographed 1/10/94 by M. Malin

Cavernously weathered boulder in the Olympus Range, Southern Victoria Land, Antarctica, at 77 deg 36.2 min S, 160 deg 57.9 min E, at 1578 m (5180 ft). Many granite and dolerite boulders in moderately to old glacial moraines show evidence of cavernous weathering. This form of weathering can develop by either or both of two mechanisms: case hardening and core softening. In the former, silica or other minerals are precipitated into microfractures, strengthening the outer portion of the rock against the attack of other physical and chemical processes. In the latter, water-assisted chemical and physical weathering dis-integrates individual crystal grains from one another, while the rock still maintains its three-dimensional integrity. Attack by wind action and frost or salt wedging eventually cracks the "shell" of these rocks, and the softer interior materials break down and are removed by wind and gravity.

- Photographed 1/12/94 by M. Malin

Test rack of basalt chips in Victoria Valley, Southern Victoria Land, Antarctica, at 77 deg 23.9 min S, 161 deg 52.0 min E, at 378 m (1240 ft). This site is investigating the effects of wind-driven sand on natural materials exposed for long periods of time in the cold desert environment. The rocks on the right actually perturb the wind flow sufficiently to modify the amount and nature of abrasion on the lower portions of this rack, but two nearby racks are not similarly affected, which permits the effects on the lower samples to be determined. This site was activated during the 1983-1984 austral summer, and samples have been returned after 1, 5, and now 10 years. Other samples seen on the rack will be returned 15, 20, 30, 40, and 50 years after the initial deployment. The heights of the rock targets were selected to provide good sampling of the lower portion of the boundary layer, where most of the sand is transported.

- Photographed 1/14/94 by M. Malin

View to southeast from the north slope of Victoria Valley, towards the eastern portion of the Olympus Range. This location, one of eleven sites at which chemical and physical weathering of rock materials is under study, is at 77 deg 22.0 min S, 161 deg 58.6 min E, at an altitude of 713 m (2340 ft). The light rock on the far mountains is granite; the dark rock cutting that material is dolerite that has intruded through the granite. The boulders in the foreground are dolerite--this site is in material corresponding to the dark unit on the north side of the valley. The light blue in the center left is a portion of Lake Vida, an ice covered, perennially frozen paternoster lake.

- Photographed 1/8/94 by M. Malin

View east down the central Wright Valley, Southern Victoria Land, Antarctica. The alpine glaciers feeding into this ice-free valley (one of a very few in Antarctica) are, from left to right, the Goodspeed, Hart, Meserve, and Bartley Glaciers, named after field assistants (graduate students) of Robert Nichols during his pioneering studies of the glacial history of these valleys during the International Geophysical Year and subsequent field seasons. This image clearly shows the classic U-shaped cross section of a glacially-eroded valley. Close inspection also shows that the valley wall is in fact compoundly U shaped, reflecting multiple episodes of glaciation. From his studies during the IGY, Troy Pewe first proposed that these valleys had experienced several episodes of glaciation; this view has been substantiated by many subsequent investigators, and the details have been further amplified by, among others, George Denton, a Professor at the University of Maine who was another of Nichols' assistants.

movie #1 (480,188 bytes) - Photographed 1/14/94 by M. Malin

This short video shows artifically shaped rocks that have been placed on the surface to observe their behavior and weathering over the course of the 50 year study. Each cube, made of native Antarctic granite, is about 8 cm on a side. Visible below each cube is a 2.5 cm diameter, 5 cm long cylinder made of native dolerite. The first cube and cylinder, left fully resting on the surface, have moved from their intial postition by a combination of wind gusts, and substrate erosion (undermining). The cube's shape has clearly influenced this process, but movement of the cylinder, despite its more aerodynamic shape, suggests that shape is not the sole factor governing this motion. The second pair of artifically shaped rocks were half-buried in the sandy substrate. As expected, these have not moved, but material has been moved around them differentially, such that they will likely be partially exhumed and ultimately also move by rotation. This part of the study suggests that, in the absence of other competing processes, and when substrate conditions permit, some rocks experience considerable motion (mostly tumbling) on geologically short timescales.