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The article discusses the dangers of Antarctic ice shelf melting. Topics including crackup has begun at the foot of Antarctica's vulnerable Thwaites Glacier, whose melt water is already responsible for about 4% of global sea level rise; sign of impending failure is a set of diagonal fractures that nearly span the entire shelf; and incursions of warm ocean water beneath the shelf, which expedition scientists detected with a robotic submersible.

The transition from limited-slip conditions at the base of grounded ice to free-slip conditions beneath floating ice occurs across the few-kilometers-wide grounding zone. This region involves either an elastic flexural transition from bedrock to hydrostatically supported elevations (often tidally influenced), a transition from thicker to thinner ice over a flat bed, or some combination of these two processes. In either case, ice must flow across a changing stress field, often resulting in brittle deformation, manifested as basal crevassing. Thus the position and morphology of basal crevasses reveal important information about the stress state across this transition. Our gridded ground-based radar surveys on Whillans Ice Stream, West Antarctica, indicate a complex pattern of basal crevasses, but most are associated with regions where the surface elevation gradient is steepest. Due to the high reflectivity of sea water, we image many off-nadir crevasses from a corner-reflector geometry involving reflections from the ice/sea-water interface and then from the crevasse, producing echoes with an inverted phase that could be misinterpreted as subglacial returns. Our results indicate that basal crevasses offer a rich dataset for diagnosing stress state and salient processes across grounding zones, and that special care is needed when interpreting subglacial returns in radar data. [ABSTRACT FROM AUTHOR]

There remain large regions of scientific interest in the Antarctic that are not instrumented. These include highly dynamic ice streams and glaciers that are difficult or impossible to reach safely because heavy crevassing impedes an overland trek or an aircraft landing. We have developed an alternative strategy for instrumenting these regions: an aerodynamic sensor that can be dropped from an overflying aircraft. During freefall the sensor accelerates to its terminal velocity of 42 m s-1 before impacting with the glacier. On impact it partially buries itself in the snow while leaving an antenna mast protruding high above the surface to ensure a long operating life. In this paper, we describe the design and results of testing this aircraft-deployable sensor. Finally we present the initial results of two campaigns to instrument inaccessible regions of Pine Island Glacier, West Antarctica, and Scar Inlet, Antarctic Peninsula, with GPS receivers. [ABSTRACT FROM AUTHOR]

The authors discuss the use of ground penetrating radar (GPR), global positioning system (GPS) and remote sensing to investigate features in Larsen C Ice Shelf that are visible in the MODIS mosaic of Antartica. They provide a comparison between the surface and basal crevasses in terms of their GPR and satellite image signatures. They conclude that all features visible in MODIS imagery of ice shelves must be basal crevasse troughs.

The article presents a study in the evolution of a western rift zone in Fimbul Ice Shelf, Antarctica. It mentions that the ice shelf is charcterised by large crevasses and rifts in Jutulstraumen which is an outlet glacier that flows in Fimbulisen. It also notes the application of a high-resolution radar imaging system and radio echo sounding data for the analysis of the rift area's surface and structure.

Zircon U-Pb ages from glacial clasts in Quaternary tills of the central Transantarctic Mountains indicate the presence of Grenville-age crust along the Ross Sea margin of East Antarctica. The polymict tills contain a variety of igneous, metaigneous, and metasedimentary clasts with Proterozoic ages not known from basement exposure. Four orthogneiss clasts have igneous ages of ∼1065-1100 Ma and Ross Orogen metamorphic overgrowths of ∼500-550 Ma. The latter ages indicate that these clasts are not glacially far traveled. Grenville-like signatures also come from a paragneiss containing detrital zircons ranging from 925 to 1130 Ma, an early Ross granitoid (∼563 Ma) containing inherited zircons of ∼1020 Ma, and detrital zircons from Neogene and Quaternary glacial deposits with a. composite age peak of ∼1045 Ma. Other igneous clasts with ages of ∼1460, ∼1580, and ∼1880 Ma provide further evidence of Proterozoic crust and corroborate earlier finding of an ∼1440-Ma A-type granite clast with isotopic signatures matching similar-age granites in Laurentia. Together, the glacial clasts indicate that ∼1.1-Ga Grenville-age igneous crust lies beneath the ice sheet along the Ross Sea margin of East Antarctica. The clast ages are similar to those of Mesoproterozoic relicts in other parts of East Antarctica, and they resemble the ages of basement rocks in western Laurentia, including igneous rocks in west Texas (1070-1120 Ma) where the Grenville Orogen (sensu stricto) terminates abruptly, or, alternatively, metamorphic assemblages within Proterozoic rift-margin strata of northern Idaho (1000-1150 Ma). The glacial clasts provide new evidence that an ∼1.1-Ga-age belt extends from western Laurentia into central East Ant- arctica inboard of the present-day Pacific margin, supporting both the SWEAT (southwest U.S.-East Antarctic) fit of Rodinia cratons and the suggestion that a Mesoproterozoic orogen integral to Rodinia assembly crosses East Antarctica. [ABSTRACT FROM AUTHOR]

The article discusses a study which utilized a linear elastic fracture-mechanics theory and a boundary element numerical method to investigate the propagation of long fractures in the Ronne Ice Shelf in Antarctica. The authors digitized a feature map of the Ronne-Filchner Ice Shelf using the MODIS Mosaic of Antarctica (MOA) image map and analyzed fractures from the outlet of Evans Ice Stream (EIS) leading downstream. Several experiments were conducted to investigate the importance of structural boundaries in crack tip arrest.

In Antarctica, radar altimeter measurements are sensitive to dielectric and penetration properties of the sensed medium (snow) such that the spacecraft''s altitude can be biased. Since 2002, relatively low frequency radar measurements over the Amery Ice Shelf, east Antarctica, have been acquired using the Envisat dual frequency altimeter at S (3.2 GHz) and Ku (13.6 GHz) bands, which penetrate a few meters into the firn. The altimeter signal is however modified in summer by the presence of snowfilled crevasses. Indeed, the specularity of the snow surfaces in summer makes the altimetric signal sensitive mostly to nadir echoes, that increases the ratio between the crevasse signal and the surrounding ice-shelf signal at nadir. Crevasses are distinguished by differences in backscattering behavior compared with the surrounding ice-shelf signal. Crevasses are characterized by a strong backscatter coefficient at Ku band and anomalies in the S band altitude estimation. These two characteristics make snowfilled crevasses detectable by the dual frequency altimeter of Envisat. We first retrieve the geometric properties of the crevasses using a hyperbolic shape function, created by strong crevasse backscatter in the Ku waveform measurements. From this retrieved crevasse signal and further waveform analysis, we assess the properties of the snow surface and its sub-surface. The crevasse, due to its small size compared to the altimeter footprint, is found to be an excellent target to study snow properties of the ice-shelf. The anomalies in the S band altitude measurements over crevasses can then be explained by the presence of a double echo in the S band waveforms. This echo is attributed to a reflection at the base of the snowbridge, where we see evidence of sub-surface echos in the individual altimeter waveforms. Based on this observation, a methodology is developed to estimate the thickness of the snowbridge. We calculate the penetration depths in the summer snow surface of the Amery at Ku band, that is found to be around 6 m. [Copyright &y& Elsevier]

The article discusses the use of TerraSAR-X to calculate the ice stream of Recovery Glacier system in Antarctica. It notes that TerraSAR-X can be used to investigate fine structures on ice and snow surfaces as well as offers good observations on features like flow lines and crevasses. It mentions that the Recovery Glacier system plays a significant role in releasing East Antarctic ice to the sea. It also examines the importance of ice sheet surface velocity in assessing ice sheet balance and in figuring controls on ice sheet dynamics.

The article offers information on the study on ice cracks and crumbling on the Antarctic region using acoustic instruments designed to detect nuclear explosions. Seismologists attributed the breaks and cracks in the ice shelf to the tectonic movement traced through sound waves using satellites. The sound of an ice mountain cracking quickly dissipates through thousands of kilometers in the water. Three hydrophone arrays in the Indian Ocean, designed to detect nuclear explosion, reveals the origin of sounds from distant ice cracking.

This article informs that two members of a five-person team from the Argentine Antarctic Institute have been missing since September 17, after falling into a deep crevasse in the Antarctic ice. the other members managed to avoid the crevasse and were rescued from the danger zone the following morning by a Chilean helicopter. A rescue effort, delayed 1 day because of a storm, has found no trace of the missing men, although there was faint hope of finding the men alive.