Research group Alluvial Fans - Universiteit .Alluvial Fans Tjalling de Haas ... What is an alluvial

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Text of Research group Alluvial Fans - Universiteit .Alluvial Fans Tjalling de Haas ... What is an alluvial

  • 2-4-2014

    1

    Research group River and delta morphodynamics

    Alluvial Fans

    Tjalling de Haas (t.dehaas@uu.nl)

    How did this boulder get here?

    Today

    General intro on alluvial fans

    Processes that act on alluvial fans

    BIG QUESTIONS:

    Which three (genetic) types of alluvial fans exist?

    What is the difference between fluvial and debris flow?

    What determines whether a fluvial or debris flow occurs?

    Fan- or cone-shaped deposit of sediment

    Develops at catchment-valley transition

    What is an alluvial fan?

    Catchment

    Apex

    ADL

    IDL

    Primary processes

    Rock-gravity processes

    Sediment without fluid transported by gravity force

    Sediment-gravity processes

    Sediment and fluid transported by gravity force

    Fluid-gravity processes

    Sediment moved by the force of water

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    Rock gravity processes

    Processes:

    Rock fall

    Rock slides

    Granular flow

    Fans:

    Steep (20-35; near angle of repose)

    Restricted radial length (

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    Debris-flow

    Excess pore pressure

    Fine particles (mud and fine silt) block pores

    Water unable to escape

    Mixture behaves as a slurry Bingham Liquid!!!

    Debris-flow morphology

    Levees

    Lobes

    Atacama, Chile 16/46

    Atacama, Chile

    17/46

    Svalbard

    18/46

    Svalbard

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    19/46

    Svalbard Utrecht

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    Real debris flow

    https://www.youtube.com/watch?v=51C7vEAVbxk

    Note:

    Plastic flow behaviour

    Large boulders in the flow

    Large particle size range

    Debris-flow fans

    1. Dominated by leves

    Steep slope (9-18)

    2. Proximal leves and distal lobes

    Proximal steep slope (9-18)

    Distal lower-sloping (3-6)

    3. Dominated by lobes

    Slope 3-8

    Blair and McPherson, 2009

    27/46

    Mars

    Debris-flow fan deposits

    Very poorly sorted

    No stratification

    Random clast orientation

    No grading

    Sometimes inverse grading

    Atacama, Chile Atacama, Chile

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    How did this boulder get here?

    Atacama, Chile

    Fluid-gravity processes

    Processes:

    Stream-flow

    Hyperconcentrated-flow

    Fans:

    Low slope (2-5)

    Sediments:

    Finest-grained fan types (dominantly gravel)

    Svalbard, Norway

    Sheetflood

    Channel

    Atacama, Chile

    Svalbard Atacama, Chile

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    Fluvial deposits

    Moderately-well sorted

    Stratification

    Normal grading

    Imbrication

    Remember Debris-flow?

    Very poorly sorted

    No stratification

    No grading

    Random clast orientation

    Death Valley, USA

    When fluvial or debris flow?

    When fluvial or debris-flow?

    Catchment is the key:

    Slope

    Drainage system

    Lithology

    Production of Mud and fine Silt

    Fine sediment needed to maintain excess pore pressure

    Secondary processes

    Reworking by:

    Water

    Winnowing of fines

    Rills, gullies and coarse lags

    Wind

    Winnowing of fines

    Deposition of aeolian fines

    Weathering

    Particle break-down

    Tectonics

    Atacama, Chile

    Inactive surface

    Active surface

    800m

    Sea

    Atacama, Chile

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    How did this fan form?

    How did this fan form?

    How did this fan form? How did this fan form?

    Remember: big questions?

    Which three main genetic types of alluvial fans exist?

    What is the difference between fluvial and debris flow?

    What determines whether a fluvial or

    debris-flow occurs?