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Aganippe Fossa

The image shows a portion of the lower flank of Arsia Mons with the aureole and a part of the large Aganippe Fossa tectonic graben structure. Dark, wind-blown dust/sand deposits create an interesting striated pattern and in the smooth regions of the image (northern/right section) many lava flows can be found at closer inspection.

Arsia Mons is a shield volcano and the southernmost of the three Tharsis Montes volcanos, located on the Tharsis bulge. The giant volcano measures 435 km in diameter and rises more than 9 km above the surrounding plains. It stands out from the other giant volcanic shields of Tharsis with its collapse caldera measuring 128 x 113 km, the largest on Mars. Arsia Mons also possesses a so-called “aureole”, an ice related flow feature and a common signature of the Tharsis Montes.

The Arsia Mons aureole covers more than 100,000 km2 and is developed only at the northwestern flank of the volcanic edifice. A reason for this could be that the prevailing NW winds generated an asymmetric ice ablation and the ice consequently accumulated only on the lee side of the volcano. Within the image, two main characteristic features of the aureole can be identified. A hummocky terrain, forming the central part of the structure and a lobate terrain, burying parts of the hummocky terrain.

The Aganippe Fossa shows a length of roughly 600 km and the bounding graben walls are 3 to 7 km apart. The formation of the Aganippe Fossae is discussed. Some scientists suggest that it represents an isolated member of the Thaumasia Fossae group, other interpretations suggest the late stage intrusive activity at Olympus Mons that formed the giant dikes in the region.