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| Titel |
Micro-relief and geometry of ice-wedge polygons in Adventdalen (Svalbard, Norway) |
| VerfasserIn |
M. Lousada, M. Jorge, J. Saraiva, P. Pina, 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 |
250068275
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| Zusammenfassung |
| Ice-wedge polygons mostly occur in flat areas, but they have also been found in slopes
with gradients as high as 25Ë ; in these cases, they are commonly elongated in
the downward direction. However, even seemingly flat terrains exhibit small-scale
topography; in this work, we conduct a detailed analysis of polygon shape in relation
with micro-relief in a polygonal network in the Adventdalen valley, in Svalbard
(Norway).
In the frame of the ANAPOLIS (Analysis of Polygonal Terrains on Mars based on Earth
Analogues) project, we have made two field campaigns to fully characterize an extensive
polygonal network (with an area circa 80x103 m2) in this periglacial area in the Arctic
(78Ë N). Included in this, a topographic survey was conducted with a GNSS-RTK
geodetic system. X, y and z coordinates were collected in a grid, approximately
every 5 meters along parallel lines separated by 10 meters. The central area of the
network, comprising close to 150 polygons, was subject to an even more detailed
coverage, with coordinates collected approximately 2 meters apart along the whole
contour of each polygon, as well as in its center. A Digital Terrain Model (DTM) was
interpolated from 8166 x, y, z points gathered in the two campaigns. The detailed
central area, with 40000 m2of polygonal terrain, was considered an ideal test field to
study the geometry of the polygons and investigate its variations in relation with
micro-topography.
The methodology employed consisted in determining the lengths of major and minor
axes for the polygons in the test area, while the elevation of the terrain on both
extremities of each axis was obtained from the DTM. From this, the rise or Vertical
Distance (VD), the difference in elevation between two points, was calculated for
the two axes of the polygons. The relation between length of axis and respective
vertical distance was assessed: it shows that VD is generally greater for the major
axis.
Eccentricity or elongation was calculated from the ratio between the major and minor axis
of the envelopes (the minimum rectangular area that covers the polygon geometry) of the
polygons, to evaluate if there is a correlation between the slope of the terrain and the
elongation of polygons.
Preliminary results point to an existing relation between the orientation of the major axis
of polygons and that of the slope of the terrain; in other words, the distribution of major axis
orientations follows closely the distribution of slope gradients. |
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