Rahe (crater)

Description

The crater has an elongated shape measuring 35 km by 18 km and is the result of an oblique impact. A channel connects Rahe crater to the vicinity of the summit caldera of Ceraunius Tholus, with an interesting fan-shaped deposit at the lower end.

Rahe crater is 1 km deep in places, and was created by a low angle impact which is evident by its elongated shape and ejecta deposit in the shape of a "butterfly". Rahe is believed to once have held a lake. The lake was formed because heat from the nearby volcano Ceraunius Tholus melted glaciers. Melt water first collected in the caldera of Cerunius Tholus, and then spilled over the caldera rim forming a valley and the lake in Rahe crater. The valley that carried the water was about 200 m wide. A delta formed where the valley entered the crater.

This type of event involving volcanic heat melting glaciers is common in Iceland. Eruptions under glaciers are called jökulhlaups and average two each century. Studies of climate change show that many low-latitude regions accumulated large amounts of snow when the climate was different.

Wikirahe.jpg|Rahe crater, as seen by CTX camera (on MRO). Wikirahedelta.jpg|Delta in Rahe crater, as seen by CTX camera. Note: this is an enlargement from the previous image of Rahe Crater.

References

References

1. {{gpn. 4926
2. Gault, D. J. Wedekind. 1978. Experimental studies of oblique impact. Proc. Lunar Planet. Sci. Conf. 9, 3843-3875.
3. Nyquist, L. 1983. Do Oblique Impacts Produce Martian Meteorites? Proc. Lunar Planet. Sci. Conf. 13, pt.2 Geophys. Res. (Supp.) 88S, A785-A798.
4. Fassett, C. J. Head. 2007. Valley Formation on Martian Volcanoes in the Hesperian: Evidence for Melting of Summit Snowpack, Caldera Lake Formation, Drainage and Erosion on Ceraunis Tholus, Mars. Icarus: 189, 118-135.
5. Bjornnson, H, F. Palsson, M. Gudmundsson. 2000. Surface and bedrock topography of the Myrdalsjokull ice cap, Iceland: The Katla caldera, eruption sites and routes of jökulhlaups. Jokull: 49, 29-46.
6. Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flor and glaciation on Mars. Nature:434,346-351.
7. Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change. Earth Planet. Sci. Lett. 241,663-671.