Martian megaflood-triggered chaos formation, revealing groundwater depth, cryosphere thickness, and crustal heat flux Export

@article{citeulike:400271, abstract = {Ravi Vallis is an outflow channel complex that emerged from Aromatum Chaos, a region of collapsed ground in Xanthe Terra, Mars. I propose that the megaflood that carved Ravi Vallis incised the crust more than 700 m, penetrated the cryosphere, and triggered the release of groundwater and genesis of secondary chaos zones in the deepest parts of the channel system. Discharge rates of 4 \&times; 10⁶ to 5 \&times; 10⁷ m³ s^\&\#8722;1 are estimated for early overland flooding. Assuming bank-full flow would yield unrealistic discharge rates of \&gt;3 \&times; 10⁸ m³ s^\&\#8722;1. Waning stage flooding in an inner channel had a discharge rate on the order of <img src="/journals/tag-image/lsim.gif" alt="\&\#8818;">1 \&times; 10⁶ m³ s^\&\#8722;1. The cryosphere thickness and groundwater depth are estimated as the sum of the channel incision depth and the thickness of residual cryosphere beneath the channel floor that could be disrupted by high artesian pressure. The surface elevation (\&\#8722;1231 m) of a transient water body in Aromatum Chaos would have controlled the maximum potentiometric heads in confined aquifers to the east. Where Iamuna Chaos was spawned, the floor of Ravi Vallis would have experienced upward hydraulic pressures of \&\#8804;2.4 MPa, enough to rupture a basaltic rock layer \&\#8804;255 m thick. At the time of the flood the cryosphere thickness and groundwater depth would have been 700 to 1000 m at this location on the equator, indicating a relatively cold, long-term climate trend similar to that of present-day Mars. The crustal heat flux likely exceeded 50 mW m^\&\#8722;2 at Iamuna Chaos. If deep lakes existed at that time in the ancestral Valles Marineris, their ice covers are estimated to have been less than 3 km thick. The fluvial incision and groundwater breakout model described here can fully account for the inception of Iamuna Chaos, Oxia Chaos, and a smaller unnamed chaos. Therefore a locally enhanced crustal heat flux was not required to initiate the formation of these chaotes.}, author = {Coleman, Neil M.}, citeulike-article-id = {400271}, citeulike-linkout-0 = {http://www.agu.org/pubs/crossref/2005/2005JE002419.shtml}, citeulike-linkout-1 = {http://dx.doi.org/10.1029/2005JE002419}, day = {24}, doi = {10.1029/2005JE002419}, journal = {Journal of Geophysical Research}, keywords = {groundwater, mars}, month = {September}, pages = {E12S20+}, posted-at = {2005-11-18 20:46:29}, priority = {4}, title = {Martian megaflood-triggered chaos formation, revealing groundwater depth, cryosphere thickness, and crustal heat flux}, url = {http://dx.doi.org/10.1029/2005JE002419}, volume = {110}, year = {2005} }

TY - JOUR ID - citeulike:400271 L3 - citeulike-article-id:400271 N2 - Ravi Vallis is an outflow channel complex that emerged from Aromatum Chaos, a region of collapsed ground in Xanthe Terra, Mars. I propose that the megaflood that carved Ravi Vallis incised the crust more than 700 m, penetrated the cryosphere, and triggered the release of groundwater and genesis of secondary chaos zones in the deepest parts of the channel system. Discharge rates of 4 &times; 10⁶ to 5 &times; 10⁷ m³ s^&#8722;1 are estimated for early overland flooding. Assuming bank-full flow would yield unrealistic discharge rates of &gt;3 &times; 10⁸ m³ s^&#8722;1. Waning stage flooding in an inner channel had a discharge rate on the order of <img src="/journals/tag-image/lsim.gif" alt="&#8818;">1 &times; 10⁶ m³ s^&#8722;1. The cryosphere thickness and groundwater depth are estimated as the sum of the channel incision depth and the thickness of residual cryosphere beneath the channel floor that could be disrupted by high artesian pressure. The surface elevation (&#8722;1231 m) of a transient water body in Aromatum Chaos would have controlled the maximum potentiometric heads in confined aquifers to the east. Where Iamuna Chaos was spawned, the floor of Ravi Vallis would have experienced upward hydraulic pressures of &#8804;2.4 MPa, enough to rupture a basaltic rock layer &#8804;255 m thick. At the time of the flood the cryosphere thickness and groundwater depth would have been 700 to 1000 m at this location on the equator, indicating a relatively cold, long-term climate trend similar to that of present-day Mars. The crustal heat flux likely exceeded 50 mW m^&#8722;2 at Iamuna Chaos. If deep lakes existed at that time in the ancestral Valles Marineris, their ice covers are estimated to have been less than 3 km thick. The fluvial incision and groundwater breakout model described here can fully account for the inception of Iamuna Chaos, Oxia Chaos, and a smaller unnamed chaos. Therefore a locally enhanced crustal heat flux was not required to initiate the formation of these chaotes. JF - Journal of Geophysical Research TI - Martian megaflood-triggered chaos formation, revealing groundwater depth, cryosphere thickness, and crustal heat flux VL - 110 SP - E12S20 KW - groundwater KW - mars AU - Coleman, Neil PY - 2005/09/24/ UR - http://dx.doi.org/10.1029/2005JE002419 ER -