Download Fluvial erosion

Landscapes:
Why, How & Their Dynamics
Dr. F. Kenton “Ken” Musgrave
West Virginia University
Pandromeda Inc.
F. Kenton “Ken” Musgrave
VICCS Spring School 2015
Earth’s Climate History
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
[roll the plantary zoom video]
F. Kenton Musgrave
VICCS Spring School 2015
My Favorite Fractal:
What is This?
F. Kenton Musgrave
VICCS Spring School 2015
How Big Is It?
F. Kenton Musgrave
VICCS Spring School 2015
Fractal Dimension
F. Kenton Musgrave
VICCS Spring School 2015
Fractional Brownian Motion (fBm)
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
Ubiquity of 1/f (or “Scaling”) Noises
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
Multifractals: a Second Approximation
F. Kenton Musgrave
VICCS Spring School 2015
Why Terrain on Earth?
From the Top
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
Pair Instability Collapse Supernovae
 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
F. Kenton “Ken” Musgrave
VICCS Spring School 2015
Pair Instability Supernovae
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
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?
F. Kenton Musgrave
VICCS Spring School 2015
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
F. Kenton Musgrave
VICCS Spring School 2015
Exponential Decay of Heat Over Time
F. Kenton Musgrave
VICCS Spring School 2015
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
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
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.
F. Kenton Musgrave
VICCS Spring School 2015
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.
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
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
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
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
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
Dynamic Fluvial Erosion Models
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
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!
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015
F. Kenton Musgrave
VICCS Spring School 2015