Phreatomagmatic explosive origin of Hrad Vallis, Mars

Wilson, Lionel and Mouginis-Mark, Peter J. (2003) Phreatomagmatic explosive origin of Hrad Vallis, Mars. Journal of Geophysical Research E: Planets, 108 (8): 5082. ISSN 0148-0227

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Hrad Vallis is a ∼370 m deep, ∼800 km long depression located at 34°N, 218°W, in Elysium Planitia, Mars. A distinctive deposit, present on both sides of the source area of Hrad Vallis, has a maximum width of ∼70 km along the strike of the depression, a lower unit extends for nearly 100 km away from the depression on either side, and an upper unit extends for ∼50 km. Viking and Mars Orbiter Camera (MOC) images show lobate deposit boundaries, rheomorphic deformation, and numerous craters 270-580 m in diameter within the deposit. The deposit coincides with a broad topographic rise ∼30 km wide and ∼100-150 m high extending along the sides of the valley for at least 100 km along strike. We propose that these features formed when a dike underlying the axis of the valley generated a shallow sill, which in turn is partly responsible for the rise topography. The remainder of the rise consists of a mud-like deposit of ejecta from a large-scale phreatomagmatic explosion due to violent mechanical and thermal mixing between the central part of the sill and ice-rich rock layers in the upper few hundred meters of the crust in a fuel-coolant-type interaction. The observed range and thickness of ejecta and the depth of the Hrad depression imply explosion steam pressures up to 360 MPa, ejecta speeds of ∼400 m s-1, and a sill at least 150 m thick intruded at a depth of ∼350-400 m below the original surface.

Item Type:
Journal Article
Journal or Publication Title:
Journal of Geophysical Research E: Planets
Uncontrolled Keywords:
?? explosive volcanismhrad vallisigneous intrusionmagma-volatile interactiongeophysicssoil scienceearth-surface processesspace and planetary scienceearth and planetary sciences (miscellaneous)atmospheric science ??
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22 Jun 2019 09:16
Last Modified:
15 Jul 2024 19:29