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| Titel |
Geometric and Topologic Characterization of Periglacial Polygonal Networks in Adventdalen, Svalbard, Norway |
| VerfasserIn |
J. Saraiva, M. Lousada, P. Pina, L. Bandeira, G. Vieira |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068427
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| Zusammenfassung |
| Polygonal terrain patterns commonly occur in periglacial regions of the Earth, where seasonal
processes of freezing and thawing cause the soil to expand and contract, leading to the
formation and growth of cracks. Understanding the formation of this type of networks on the
Earth and tracing their evolution (including differentiating ages of formation) can provide us
with many insights into the history of similar patterns on Mars, in whose surface
they occupy vast extensions, most likely due to the presence of frozen water in the
soil.
Thus, analogue studies of this type of structure on the Earth are important. In this work,
we describe the geometric and topologic characteristics of a number of networks of
ice-wedge polygons occurring in a coastal valley, the Adventdalen, on the Norwegian
archipelago of Svalbard, in the Arctic, at 78Ë N. The aim of the study is to try and find the
similarities and differences between them and to relate those with factors such as soil
characteristics and topography.
Given the logistic problems in conducting a complete on site study of all those networks,
spread out over many kilometers, the study was conducted through the analysis of remotely
sensed imagery: 53 images (four-band RGB+NIR and 0.2 m/pixel of spatial resolution),
acquired by the Norwegian Polar Institute in 2009 during their aerial photogrammetric
campaign, were purchased and processed. They were orthorectified with an ASTER
Global Digital Elevation Model (a product of METI and NASA). Polygonal networks
were identified and digitized into a GIS. They occupy a total area of almost 10
km2.
The areas covered by the individual networks studied range between 4x103
and 106 m2. Individual polygon sizes vary widely, from 6 to 7x103 m2, with an
average of 300 m2. The variation is less pronounced for the networks that are most
clearly traceable in the images (which reduces typical errors such as those that create
large polygons occupying the area of several smaller ones that go unnoticed in the
images).
For each polygon present in the networks studied, topological parameters such as number
of neighbors and valences of the vertexes were obtained, using an automated process
previously developed by this team for the analysis of Martian networks. Shape descriptors
like area, circularity, compactness and elongation were also calculated. The analysis of this
multivariate data is being performed, with the goal of determining what, if any, are the
relations between terrain morphology and network presence, and its influence on polygon
geometry.
Favorable topographic conditions for network formation seem to be flat terrains with
water accumulation zones, although they can be found in slopes with gradients up to 25o. It is
believed that larger polygons are older, and that, after repeated seasonal freezing and thawing,
new and thinner cracks form inside the early polygons, thus dividing them into smaller ones. |
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