INTRODUCTION

RESULTS

CONCLUSION

METHODS

Micro-relief and geometry of ice-wedge polygons in Adventdalen (Svalbard, Norway)

M. Lousada(1), M. Jorge(2), J. Saraiva(1,3), P. Pina(1), and G. Vieira(2)

(1)Instituto Superior Técnico, Lisboa, Portugal, (2)CEG / IGOT, Lisboa, Portugal, (3)UNIS, Longyearbyen, Norway

Ice-wedge polygons mostly occur in flat areas, but they have also been found in slopes with gradients as high as 25°; 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 40,000 m2) in this periglacial area in the Arctic (78° N).

Shows a marked difference between VDs for the two axes, again illustrating the fact that major axes correspond to higher VDs

Shows higher Vertical Distance values for major axis.

Density plot for Major and minor axis vertical distances density distributions. Several minor axis have less then 20 cm of vertical distance.

1) Box Plot

2) Quantile-Quantile Plot

3) Density Plot

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.

C DETERMINING VERTICAL DISTANCES ALONG THE AXIS 3

2

It is often observed, on hillsides, that ice-wedge polygons are elongated in the direction of maximum slope. In this work, the analysis of detailed and precise topographic data suggests that the geometry of polygons, even in this rather smooth area, is not completely random, and that there is a statistically relevant connection to the existing micro-relief .

Research developed within the project ANAPOLIS (PTDC/CTE-SPA/099041/2008),funded by FCT (Portugal)

Adventdalen Topographic map and ESRI Base Maps

1

A DTM was generated by interpolation from the 8166 (x,y,z) points gathered with the GPS in the course of the two campaigns. The delineation of polygons was achieved through analysis of aerial images combined with field information.

The combination of all that information led to the construction of a detailed model of the micro-topography in the central area of the network, covering 163 polygons. Thus, we can now evaluate the relation between geometry and micro-relief fluctuations for this set of low-centred polygons.

Two field campaigns were conducted, in 2010 and 2011. The precise location of points in the field was determined through the use of a GNSS-RTK geodetic system.

B DTM DERIVED FROM THE FIELD SURVEYS

85 % OF THE 163 POLYGONS HAVE A HIGHER VERTICAL DISTANCE ALONG THE MAJOR AXIS

In the central area of the network, the contours of 121 polygons were also surveyed. Coordinates were collected at the centre of the troughs separating adjacent polygons.

A gridded topographic survey was conducted by collecting x, y and z coordinates every 5 meters along parallel lines separated by 10 m. This was complemented with the collection of more points in the areas between the lines.

The central part of the network was later subject to an even more detailed coverage. Approximately 150 polygons were surveyed, and coordinates were collected also at several locations along the transversal profile of troughs.

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.

A FIELD SURVEYS