9.2 Shaping Planetary Surfaces

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University of Toronto St. George
Astronomy & Astrophysics

9.2 Shaping Planetary Surfaces Impact Cratering -the blasting of bowl-shaped impact craters by asteroids or comets striking a planets surface -impacting objects typically hit the surface at a speed between about 40,000 to 250,000 kmhr -craters are generally about 10 times as wide as the object and 10-20% deep as they are wide Volcanism -any eruption of molten rock or lava from a planets interior onto the surface, whether it comes from a tall volcano or simply rises through a crack in a planets lithosphere -occurs when magma (underground molten rock) finds a path through the lithosphere to the surface -molten rock rises because 1-generally less dense than solid rock, and lower-density materials tend to rise when surrounded by higher-density materials 2-driven upward under pressure of a chamber of molten rock being squeezed 3-molten rock contains trapped gases that expands as it rises, making it rise much faster and lead to dramatic eruptions -volcanic plains: runniest lavas that flow far and flatten out -shield volcanoes: thickening before spreading out -stratovolcanoes: thickest lava flows that cant flow very far and therefore build up tall -made by lower-density volcanic rock that erupts as a thicker lava -lava plains and shield volcanoes are made of basalt (a mixture of many different minerals that erupts from volcanoes as a high-density but fairy runny lava -all terrestrial and some jovian show signs of volcanic plains and shield volcanoes -outgassing: the process in which the release of pressure e
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