Transcript Slide 1
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 • 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 Kilauea Caldera, Hawaii 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