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Landscapes: Why, How & Their Dynamics

Landscapes: Why, How & Their Dynamics. Dr. F. Kenton “Ken” Musgrave West Virginia University Pandromeda Inc. Earth’s Climate History. [roll the plantary zoom video]. My Favorite Fractal: What is This?. How Big Is It?. Fractal Dimension. Fractional Brownian Motion (fBm).

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Landscapes: Why, How & Their Dynamics

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  1. Landscapes:Why, How & Their Dynamics Dr. F. Kenton “Ken” Musgrave West Virginia University Pandromeda Inc.

  2. Earth’s Climate History

  3. [roll the plantary zoom video]

  4. My Favorite Fractal:What is This?

  5. How Big Is It?

  6. Fractal Dimension

  7. Fractional Brownian Motion (fBm)

  8. Ubiquity of 1/f (or “Scaling”) Noises

  9. Multifractals: a Second Approximation

  10. Why Terrain on Earth? From the Top

  11. Pair Instability Collapse Supernovae Why Terrain on Earth? · Nucleosynthesis: fusion of lighter elements • Fusing elements heavier than iron is endothermic • Products must be distributed into interstellar space · Binding energy • The energy required to escape a gravity well • Equivalent to energy to reach escape velocity · What can accomplish this for heavy stars? • Ordinary core-collapse supernova: recent era, leaving remnant • Earliest epoch of star formation: PICS (pair inst. coll. su.) • Runaway nuclear reactions detonate & disrupt entire star

  12. Pair Instability Supernovae

  13. More Recent Supernovae · Much smaller than PICS • Progenitor star maybe several solar masses • Provide shorter-lived radionuclides in local dust clouds • Shock interstellar clouds triggering gravitational collapse • Thus causing formation of new stars & planets · Leave a remnant • Neutron star or black hole • Quantity of ejecta much smaller than PICS · Same kind of runaway nucleosynthesis • Radioactive ejecta cause terrain on Earth • And Earth’s magnetic field?

  14. Earth’s Internal Energy Budget · Internal energy: core heat • ~50% binding energy: heat from gravitational collapse • ~50% radioactive decay of supernova ejecta · Binding energy • Finite supply • Decays exponentially with time: cooling · Radioactivity • Primarily thorium & uranium isotopes • Radionuclides with long half-lives • Also decays exponentially, but more slowly

  15. Exponential Decay of Heat Over Time

  16. Plate Tectonics · Convection in Earth’s mantle • Unique to Earth • Mercury, Venus & Mars have none • Related to Earth’s magnetic field? · Plates are quite mobile over geologic time • Bash together, form supercontinents: Pangea, Gondwanaland • Form mountains: orogenesis · Plate dynamics • Continental cratons • Continental margins

  17. Mountain Building: What Goes Up Must Come Down · Uplift • Causes orogenesis • Limited by plasticity of Earth’s crust • Mt Everest is as tall as a mountain can get on Earth • Olympus Mons on Mars is much taller · Erosive transport • Fills in depressions: lakes become meadows • Generates arable “bottom land” (sediment is fertile) • Generates continental shelves • Generates temporary features: river deltas, barrier islands, etc.

  18. Modes of Erosion · Fluvial: water • Drainage networks • Most dynamic of modes · Glacial: ice • Slow • Powerful: moves mountains · Coastal: storm surf • Coastal erosion • Mobile barrier islands · Diffusive: various • Thermal & chemical weathering • Aeolian: mobile sand dunes & sandblasting of rock • Rain splash, animal trampling, dry creep, etc.

  19. Erosion · Erosion is what shapes terrain Bedrock is fractal; erosion works on this fractal substrate Creates context-sensitive fractals: river networks · Diffusive erosion Dry creep, rain splash, animal activity, etc. Temporal low-pass filter: easy to implement, very efficient · Fluvial erosion: running water Rivers and glaciers are principal (inland) geomorphic agents Very important—but complex and slow to compute

  20. Erosion · Thousand-year floods: extreme events • Major fluvial geomorphic events • Appear (to me) to be what really makes changes • Like redirecting the Po or Mississippi rivers · Ice ages: extreme—also the norm • Geomorphic events of greatest magnitude • Prealpine Lakes (here), Lake Baikal (Siberia), Great Lakes (USA) • Depression & rebound of crust

  21. Dynamic Fluvial Erosion Models

  22. Simulating Nonlinear Phenomena • · Fluvial erosion models (FEMs) vs. GCMs • FEMs illustrate complexity and difficulty • Solving nonlinear PDEs • Formulating ad hoc “laws” of Nature • Exploring high-dimensional parameter spaces • · Earth’s overall energy budget • Internal energy: a tiny fraction • Insolation: all the rest • · Albedo of planet Earth: reflected portion of insolation • Sun’s power spectrum Modulated by clouds Requires good cloud models—entirely missing in GCMs Aerosols, convection, phase transitions, turbulence—too hard!

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