RE: New Guinea tsunami information.

From: Joel Z. Bandstra (
Date: Sun Feb 10 2002 - 20:08:46 EST

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    In the post below, Glen wrote: "An onshore landslide simply mixes things
    up with little sorting."

    I don't think this is correct. See R.M. Iverson, The physics of debris
    flows, Rev. Geophys. v35 pp245-296 August 1997. This is not my field so
    I'm sure there is a better reference but this one should suffice.

    The observation, as I understand it, is that coarser grained material
    sorts to the edges of both landside and debris flow runouts. I guess it
    probably works just like the big nuts in the mixed nuts can floating to
    the top.

    -----Original Message-----
    From: [] On
    Behalf Of Glenn Morton
    Sent: Sunday, February 10, 2002 6:22 PM
    To: Allen Roy;
    Subject: RE: New Guinea tsunami information.

    Hi Allen,

    >-----Original Message-----
    >From: []On
    >Behalf Of Allen Roy
    >Sent: Sunday, February 10, 2002 8:47 AM

    >There is a simularity with the Haymond deposits in that the tsunami
    >deposited consisted of two layers: the bottom one of sand, the top one
    >clay/silt. To be sure the quantites of each are certainly different
    >the Haymond deposits.

    Yes, there are several differences. As you note, the quantities of sand
    shale are different in the tsunami deposit. There is the lack of marine
    burrows in the tsunami deposit which exist in the Haymond. And most
    importantly, the Haymond consistes of 15,000 layers, the tsunami
    consists of
    one pair with very, very little shale. NOw, if the tsunami had deposited
    15,000 layers of sand and shale then you might have a case. As it is,
    will have to wait several hundred years for the next tsunami at that
    The tsunami simply is not analogical to the Haymond.
    >The article also makes the following points:
    >1. "The recently deposited tsunami sand is believed to have come from
    >offshore of the beach as numerous sand dollars were found near the
    >of the deposit."

    But no burrows.

    >2. "Another common characteristic of recently deposited tsunami sand
    >normal grading (a decrease in the size of the sand grains from the
    >bottom to
    >the top in the deposit)"

    typical hydrodynamic sorting according to Stoke's Law. This is nothing

    >3. "The deposit fined landward (near the shore the sand particles were
    >larger than the sand farther inland)."

    Once again, this is what Stokes law would predict.

    >Lets start with point 1.
    >In this case, as the tsunami swept ashore it picked up beach sand
    >and nearly
    >simultaneously deposited it as it swept inland. What if, instead
    >of a sandy
    >beach, the wave had swept across a muddy delta? What would be the
    >load carried by the wave? What would be the major deposition?

    True, but most of it would have remained suspended in the draining
    waters as
    Stoke's law would not let it settle as rapidly as you require for a

    >The point being that tsunami deposition reflects the compsition of
    >the soils
    >across which the tsunami came as it swept ashore. So it could consist
    >lots of sand/little clay, or some sand/some clay, or little sand/lots

    There are several tsunami's per year. Find one with little sand and lots
    clay. I don't think you can.

    >Point 2.
    >One of the major means of identifying turbidite deposition is the fact
    >it has normal grading (although reverse grading is sometime noted),
    >sand through silt to clay. At the New Guinea tsunami depsition site
    >deposit displays "normal grading" (including clay/silt on top). This
    >confirms an off hand statement from a non-creationary geologist I
    >heard once
    >who said that tsunami and turbidite depositions were nearly

    Unamed sources, like with newspapers, are untrustworthy. Sources please.

    >Point 3.
    >The tsunami deposition also display landward fining. It is curios to
    >that ALL Grand Canyon formations display horizontal fining in one
    >or another. I wonder if anyone has checked to see if the Haymond
    >layers graded horzontally. I would not be the least bit surpried to
    >that they do grade horizontally.

    Of course they grade. Almost all clastic beds do. That doesn't mean that
    Haymond was a tsunami deposit. Your tsunami deposit has little shale and

    >> Thirdly, this is a tsunami deposit which is above sea level which
    >> shale-containing water to flow down through the porous sand as noted
    >> Below sea level, this won't happen. The water will not flow through
    >> like it does on land.
    >This is a good point. I like it! It makes deposition of clay/silt
    >faster than I had thought. It is still note worthy that the clay/silt
    >there because the tsunami picked it up and carried it into place.

    Don't jump on it for a marine deposit, which is what the Haymond is.
    Landslides on land don't sort th way that turbidites do. In the water,
    turbulence separates the shale from the sand with the sand flowing close
    the water bottom and the shale going into suspension and depositing over
    vastly larger area. Only over a long time can shale be deposited on top
    the sand in a marine environment. An onshore landslide simply mixes
    up with little sorting.

    >> So, this has nothing to do with a turbidite.
    >If it is true that turbidite and tsunami deposits are nearly
    >indistinguishable, then whos to say that the Haymond deposits are not
    >tsunami rather than turbidite deposits?

    Tsunami's and turbidites are distinguishable. You are depending upon
    some unnamed, unreferenced, unknown and possibly non-existent person is
    supposed or claimed to have said, in order to support your argument.
    Geologists can tell the difference between marine and land deposits and
    between tsunamis and turbidites.

    This is from R. Peters et al, ITS 2001 proceedings "An Overview of
    Deposits along the Cascadia Margin," p. 479

    "Tsunami deposits may be distinguished from river deposits by disntinct
    biological markers, spatial distribution, sediment characteristics, and
    geochemistry. Tsunami deposits contain marine or brackish water
    microfossils while fossils in river deposits, if present, would be fresh
    water varieties. Tsunami deposits fine landward, while river deposits
    generally fine seaward. The composition texture of the sand grains can
    used to determine a coastal or upriver source. Geochemical indicators,
    as bromine enrichment, may indicate a marine source."

    Turbites and tsunami's fine in opposite directions. Turbidites fine
    the sea, tsunamis fine toward the land. Turbidites show burrows and
    ichnotraces in the shale above the sand which is thick and tsunami's
    as the shale is too thin.


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