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EART 160: Planetary Science

EART 160: Planetary Science. Last Time. Paper Discussion Stevenson (2001) Planetary Surfaces Impacts Morphology Mechanics Ages of Planetary Surfaces Frequency and Consequences. Today. HW 2 due Today How are people doing? Planetary Surfaces Volcanism

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EART 160: Planetary Science

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  1. EART 160: Planetary Science

  2. Last Time • Paper Discussion • Stevenson (2001) • Planetary Surfaces • Impacts • Morphology • Mechanics • Ages of Planetary Surfaces • Frequency and Consequences

  3. Today • HW 2 due Today • How are people doing? • Planetary Surfaces • Volcanism • What controls where and when volcanism happens?

  4. Volcanism • An important process on most solar system bodies (either now or in the past) • It gives information on the thermal evolution and interior state of the body • It transports heat, volatiles and radioactive materials from the interior to the surface • Volcanic samples can be accurately dated • Volcanism can influence climate

  5. What is it? • The eruption of magma from the interior of the planet onto the surface, forming new rock.

  6. Phase Diagrams

  7. Why does it happen? Temperature • Material (generally silicates) raised above the melting temperature (solidus) • Increase in temperature (plume e.g. Hawaii) • Decrease in pressure (mid-ocean ridge) • Decrease in solidus temperature (island arcs) Reduction in pressure Increase in temperature Depth Normal temperature profile liquidus solidus Reduction in solidus

  8. Composition • Mantle material: peridotite • Partial melting of (ultramafic) peridotite mantle produces basalt (mafic magma). • More felsic magma (e.g. andesite, rhyolite) requires more melting, fractional crystallization • Low-temperature minerals (e.g. silica) melt first • Magma becomes more felsic with time • Ultramafic rocks no longer form today Solidus Temperatue Silica content, Viscosity

  9. Eruptions • Magma is often less dense than surrounding rock (why?) • So it ascends (to the level of neutral buoyancy) • For low-viscosity lavas, dissolved volatiles can escape as they exsolve; this results in gentle (effusive) eruptions • More viscous lavas tend to erupt explosively • We can determine maximum volcano height: h What is the depth to the melting zone on Mars? Why might this zone be deeper than on Earth? d rc rm

  10. Cooling timescale • Conductive cooling timescale depends on thickness of object and its thermal diffusivity k • Thermal diffusivity is a measure of how conductive a material is, and is measured in m2s-1 • Typical value for rock/ice is 10-6 m2s-1 cold hot Temp. d • Characteristic cooling timescale t ~ d2/k • How long does it take a metre thick lava flow to cool? • How long to boil an egg? • How long does it take the Earth to cool?

  11. Large volcano Shallow slopes Built up by multiple flows of low-viscosity magma Built up by solid fragments (ash) ejected from volcanic fent Steep Small (< 1 km high) Types of Volcanoes Shield Volcano Cinder Code

  12. Pancake Domes on Venus 65 km Magellan Radar Images • High-viscosity, silica-rich magma • High atmospheric pressure • Why do they get so big? Global resurfacing ~750 Mya

  13. Tharsis Rise on Mars Olympus Mons Tallest volcano in SS 27 km high • Up to ¼ of the planets surface • Centered on equator (why?)

  14. Lunar Maria • Giant impact basins formed during LHB (4.0 Gya) • Filled with basaltic lava (3-3.5 Gya) • Near-side ONLY

  15. Rilles • Lava Channels • often lead back to vent • Classified by shape • Sinuous • Linear • Arcuate Prinz Crater – Apollo 15

  16. Mercury • Smooth Intercrater Plains • Floor of Caloris Basin • Similar to Lunar Maria

  17. 250km Io • Volcanism is basaltic – how do we know? • Resurfacing very rapid, ~ 1cm per year • What is the eruption speed? Loki Pele April 1997 July 1999 Sept 1997 Pillan Galileo images of overlapping deposits at Pillan and Pele 400km Pele

  18. Io Tupan Patera -- Galileo The lavas of violent Io, Though they may look like pico de gallo Erupt and then rain On the sulfurous plain Looking nothing at all like Ohio. Tvashtar Plume – New Horizons

  19. Eruption Speed

  20. Cryovolcanism Rock  Ice Magma  Water Why is this hard? Caldera rim Lobate flow(?) This image shows one of the few examples of potential cryovolcanism on Ganymede. The caldera may have been formed by subsidence following eruption of volcanic material, part of which forms the lobate flow (?) within the caldera. The relatively steep sides of the flow suggest a high viscosity substance, possibly an ice-water slurry (?). Schenk et al. Nature 2001

  21. Examples Lineaments on Europa Like Mid-ocean ridges? -- Galileo Fountains of Enceladus -- Cassini Ganesa Macula on Titan -- Cassini Nitrogen Geysers on Triton -- Voyager 2

  22. Next Time • Planetary Surfaces • Tectonics

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