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Geologic Features of Mars. Lab 7. Crustal Dichotomy of Mars. Striking difference between northern and southern hemispheres Southern hemisphere is 5 km higher than northern, is 70 km thick Southern hemisphere has lots of craters of all sizes
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Crustal Dichotomy of Mars • Striking difference between northern and southern hemispheres • Southern hemisphere is 5 km higher than northern, is 70 km thick • Southern hemisphere has lots of craters of all sizes • Northern hemisphere is lower than southern, is smooth and has been resurfaced by some process that eradicated craters and is 40 km thick
Main Processes of Crust Formation • Erosion • Volcanism • Impact craters • Tectonism
Erosion • Current and dominant process • Mass movement • Landslides • Sinking • Aeolian • Dunes • Windstreaks – downwind from a crater by deposition or erosion • Water • Valleys – Valles Marineris (LA→NY), maybe a rift valley(crust breaks apart along a fault line)
Volcanism • Mars has largest volcanoes of solar system • Olympus Mons – huge volcano bigger than Hawaii, one of 4 in Tharsis • Volcanism produced • Lava flows • Shield volcanoes • Calderas
Volcanism contd • Shield volcanoes have a steep cliff wall called a scarp • They also have a caldera • the largest and most explosive volcanic eruptions eject tens to hundreds of cubic kilometers of magma. When such a large volume of magma is removed from beneath a volcano, the ground subsides or collapses into the emptied space, to form a huge depression called a caldera
Impact Craters • Produced by comets and asteroids • Tapered off ~3.8 billion years ago • Older surfaces have more craters • Older craters are larger • Older craters are more eroded • Can guess age by superposition and crosscutting
Tectonism • Mars has only 1 tectonic plate (Earth has 7) • Tectonic stress leads to subsurface uplift • Extensional stress led to valley formation • Valles Marineris is longest canyon in solar system
Tectonic Plates of Earth http://geology.er.usgs.gov/eastern/plates.html
Magnetic Field of Mars • No planetwide field • Some weakly magnetized regions in old southern highlands • Martian core has S in addition to Fe • Molten S core does not produce electrical currents, so no planetwide magnetic field