TY - JOUR

T1 - Phreatomagmatic explosive origin of Hrad Vallis, Mars

AU - Wilson, Lionel

AU - Mouginis-Mark, Peter J.

PY - 2003/8/25

Y1 - 2003/8/25

N2 - 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.

AB - 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.

KW - Explosive volcanism

KW - Hrad Vallis

KW - Igneous intrusion

KW - Magma-volatile interaction

U2 - 10.1029/2002JE001927

DO - 10.1029/2002JE001927

M3 - Journal article

AN - SCOPUS:0141621643

VL - 108

JO - Journal of Geophysical Research E: Planets

JF - Journal of Geophysical Research E: Planets

SN - 0148-0227

IS - 8

M1 - 5082

ER -