Tuesday, April 8, 2014

Swept Slopes of Herigonius

Banded layers of mare basalts uncovered by mass wasting in the eastern wall of Herigonius crater. The rim crest is outside the top of the image field of view (north is to the left). Debris and boulders accumulate downslope, below, toward the crater floor and center. 500 meter field of view from LROC NAC observation M150741485; LRO orbit 7348, January 27, 2011; incidence angle 60° at a half meter resolution from 46.46 km [NASA/GSFC/Arizona State University].
J. Stopar
LROC News System

Gravity, as well as seismic events, keep the upper slopes of the east of wall of Herigonius crater (14.86 km; 13.321°S, 326.029°E) swept clean by moving material downslope.

Herigonius is a large crater at the southernmost extent of Oceanus Procellarum.

Mass wasting reveals banded layers of mare basalt. Individual layers can be traced north to south across much of the wall of Herigonius, and as a whole, represent multiple broad, thin lava flows (see image of the east wall below).

East wall of Herigonius crater, rim crest at top of image, floor toward the bottom. Click on image to see how the layers of basalt are exposed in this part of the upper wall [NASA/GSFC/Arizona State University].
Blocky overhangs indicate areas more resistant to mass wasting and are comprised of the more coherent parts of the lava flows. However, layers of mare basalt are not exposed in all of the walls of Herigonius crater and are best observed in the eastern portion. The entire region is dominated by mare lava flows, but why are the layers so prominent in the eastern wall?

Elevation data derived from the LROC WAC instrument (GLD100) allows investigation of the topography and slopes of the Herigonius crater. The slope map (below), which is a measure of the average change in topography from pixel to pixel, shows that the eastern wall of Herigonius crater is one of the steepest parts of the crater. This steepness may help to continuously expose fresh new materials and basalt layers. Alternatively, the coherent layers of the prominent mare flows in this region are more resistant to downslope movements and can support steeper slopes that are, in turn, more resistant to the build up of debris.

Slope map (overlain on shaded-relief) of Herigonius crater, generated from the LROC WAC GLD100 product. Steeper slopes shown in red, lower angle slopes are purple and blue. Red areas, including the east wall, have slopes around 40° and correspond to outcrops of banded mare layers [NASA/GSFC/Arizona State University].
Explore the east wall in full resolution, HERE, and the entire crater, HERE.

Related Posts:
Layering in Messier A
Marius A
Outcrops in Laplace A
Apollo Basin Mare in a Sea of Highlands

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