Valles Marineris: diferència entre les revisions

Des del seu descobriment s'han assenyalat diverses causes per a l'origen del Valles Marineris. L'origen del sistema de canyons s'ha intentat explicar a partir de l'acció erosiva de l'aigua líquida o de l'activitat termocàrstica, que consisteix en la fusió del [[permafrostpermagel]] que pugui existir sota el sòl marcià, igual que succeeix en les regions de clima glacial de la Terra. A Mart l'activitat termocàrstica seria un fenomen més probable que l'erosió per part de curoso d'aigua, la presència actual de la qual en el planeta es veu impedida tant per la baixa pressió atmosfèrica existent (tan sols un 0,05% de la terrestre) com pel baix interval de temperatures regnants a la superfície (entre -36 i -125 ºC), situat per sota del [[punt triple]] de l'aigua. Una altra hipòtesi presentada per McCauley el 1972 suggeria que el canyó es va formar per la retirada del [[Magma (volcànic)|magma]] existent sota la superfície. La hipòtesi de Tanaka i Golombek, del 1989, apuntava com a causa principal una possible fractura per tensions en l'escorça planetària.

<!--The Tharsis Bulge was formed from the Noachian to Late Hesperian period of Mars. Tharsis was formed in three stages, appropriately named one, two and three. Stage one of the Tharsis construction was a combination of volcanism and isostatic uplift, soon, however, the volcanism loaded the crust to a point where the crust could no longer support the added weight of Tharsis, leading to widespread grabens in the elevated regions of Tharsis. Stage two is more volcanism and a loss of isostatic equilibrium; the source regions of the volcanism no longer resided underneath the Tharsis creating a very large load. Finally the crust failed to hold up the Tharsis and the radial fractures, like Valles Marineris, was formed. Stage three is mainly just more volcanism and the crust, because it had already reached its failure point, just stayed in place and the younger volcanoes were formed. Tharsis volcanism is a very low viscosity magma forming shield volcanoes similar to the Hawaiian Island chain, but, because there are no active plate tectonics on Mars, the hotspot activity kept loading the same spot over and over, creating some of the biggest volcanoes in the solar system, including the biggest: Olympus Mons (Cattermole, 103-104). Between the Valles Marineris proper and the Noctis Labyrinthus, slightly to the south is Oudemans Crater. This might have been the trigger for some of the features of Valles Marineris because this could have heated up the permafrostpermagel turning the carbon dioxide to liquid and then further decompression of the carbon dioxide ice could flow out of the Noctis Labyrinthus, causing a catastrophic flood of carbon dioxide liquid and gas into the northern plains.-->