Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.c31c0521z&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #C31C-0521
Mathematics
Logic
0774 Dynamics, 0776 Glaciology (1621, 1827, 1863), 0798 Modeling, 6240 Meteorites And Tektites (1028, 3662)
Scientific paper
The highest concentration of meteorites yet discovered on Earth is found in the ice sheet covering Antarctica. Major meteorite accumulation zones often occur in front of submerged or emerged bedrock obstacles, where the meteorite-bearing ice slows down, is uplifted by the buttressing effect and exhumed and concentrated by wind ablation ("ice-flow model"). Meteorite traps have also been discovered in the downstream side of major emerged bedrock barriers, as in the Frontier Mountain (FM) region, a nunatak outcropping in the Northern Victoria Land, Antarctica, 250 km from the Italian Terra Nova Base. However, recent detailed glaciological analyses indicate that also for this site the "ice-flow model" remains the best concentration explanation, being present an important submerged barrier in the main blue-ice field. A this site, during the last fifteen years, more than 1000 meteorites have been there collected. During the various field expeditions, different data were acquired to allow a detailed study of the local glaciodynamics. This large data set was used to constrain boundary conditions for performing a set of physical experiments reproducing the main glaciodynamics characteristics of the FM region. In addition to previous result, now we performed a series of experiments that consider also the ablation effect in order to better reproduce the natural environment. Analog experiments were performed at the Tectonic Modelling Laboratory of the CNR-IGG (Florence, Italy). Polydimethilsyloxane (PDMS) is used to simulate glacial flow in analog models; this material properly simulates the rheological behaviour of ice (Corti et al, 2003; Corti et al, 2008). Models are built inside a Plexiglas box with dimensions of 70cm x 20cm x 10cm. The models are scaled to nature conditions allowing a comparison between laboratories and natural models. The geometrical scaling ratio was of 2*10-5, such that 1 cm in the model represented about 500 m in nature. In order to measure the progressive ice deformation during the experiments, passive grids of carbon-black particles are printed both inside and on the model surface using the unbaked photocopy method. In a first series of experiment we tested the flow variation for submerged obstacle with dimensions 3cm x 10cm x 1÷5 cm placed inside the Plexiglas box which is inclined of 3°; the PDMS is allowed to flow by opening the front end of the box. Afterward we introduced the ablation effect in the model with emerged obstacle for two natural case: upstream and downstream of the bedrock obstacle. In these models, ablation was simulated by physically removing pieces of PDMS from the surface with a small knife at regular intervals of 30 minutes in order to maintain a constant depression on the free surface of the ice. Later we used the Frontier Mountain bedrock topographic model used for previous work with addition of ablation downstream the mountain outcrop, as in the natural environment. Experimental results show how the flow field and variations in the topography of the free surface and internal layers of the ice are strongly influenced by the presence and height of bedrock obstacles, but only limited uplift of internal layers is observed in these experiments. The exhumation of deep material embedded in the ice is observed only if ablation is be included in the physical models. In this case, the analogue ice replenishes the area of ablation (simulated by material removal), thereby allowing deep layers to move vertically to the surface and severely altering the local ice flow pattern.
Corti Gloria
Folco Luigi
Zeoli Antonio
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