Hello,

Wow, great explanation. I have a friend who is a geologist, and taken
several long car trips to conventions. I learned all kinds of things just
from him talking about the terrain we drove past.

I am surprised that there is not some opensource software that geologist use
to simulate the processes of terrain building.

I really like Celestia (open source software, kind of like a planetarium)
and use it to give night sky views from fictional planets around real stars.

LDJ

On 8/6/07, T'Star <bedlamandmayhem-at-gmail.com> wrote:
>
> I will caveat that doing tectonics accurately is VERY computationally
> intensive. Faking it should be somewhat easier. After all,
> geologists have been taking shortcuts for decades to avoid multiple
> month computation times and relatively accurately.
>
> Continental drift is simply the motion of continents due to sea floor
> spreading (the Atlantic is getting wider at the mid ocean ridge.),
> subduction (the pacific ocean plate is going UNDER the North American
> and Asian plates, so is getting smaller. The Mediterranean sea
> underwent a similar process it use to be a MUCH larger body called the
> Sea of Tethys.) Mountains are built by several processes "mountain
> building Events" tend to occure at hot spots (Hawaii, Yellow Stone)
> and the boundaries of techtonic plates. When two plates slame into
> each other they can either rotate along one another (strike slip fault
> like the San Andreas) or one can be 'pushed' under the other.
> Continental crust is much lighter than oceanic crust (Basalts, which
> make up most ocean floor are denser than granites and Andisites that
> tend to make up continental crust. Therefore they tend to go under
> these other plates.) As they go down there is folding along the edge
> of the contental crust, there tend to be earthquakes (which can cause
> uplift of the continental crust) and the subducting oceanic crust
> melts and the more bouyant liquid material rises and causes volcanoes.
> This is how the Andes mountains were formed and part of how the
> rockies were formed (though that is a much more complicated system.)
>
> Now for continent on continent collisions. When continental crust
> hits continental crust the density difference is MUCH less. The
> subcontinent of India is currently subducting (very slowly) under the
> continent of Asia. The result of this is the Himalayan mountains.
> This is a much less common type of plate collision, though it has
> happened repeatedly through out geologic history.
>
> If you look at most continents, the continental cratons (that is the
> central part of the continent that is generally geologically inactive)
> is typically quite flat. That is because mountains require tectonic
> activity, and once the uplift of the mountains STOPS, erosion and
> weathering take over and flatten them down over millions of years.
> (That is why the Appalachians are so very much shorter than the
> rockies. They are much, much older.)
>
> So when two continents "drift" into one another you get a continent on
> continent collision that results in VERY tall mountains, but usually
> you get mountain building more coastal regions, especially along
> subduction zones. (Note this is a summary of about 4 semesters of
> tectonic information. These are the basic, major ways that entire
> ranges are built. not all the dozens of different other ways that
> rocks get pushed UP.)
>
> On a programing sense, what I think they did was just put a 'gradient'
> for elevation that requirement, which set fractal boundaries and
> incrementally increased elevation... unfortunately this doesn't allow
> for large continental interior planes like the Steppes of central
> Asia. Most of Siberia, the north American great planes and Canadian
> Shield, Central Africa, and the large planar regions in South America
> that make up most of Argentina and Brazil. FWE does put some
> mountains near the coast and you can 'tweak' elevations, but there is
> a tendency for mountainous interiors, and planar coastal regions. The
> main tectonic way to generate that kind of setting is to have ALL your
> plate collision boundaries in the central areas of continents, and
> that just does not happen that universally. Especially not with the
> low proportion of seas in most of the fractally generated worlds.
> Some where, sooner or later Erosion and weathering are going to beat
> out uplift and those mountains are going to flatten... and it's not
> going to be at the same rate all over the world.
>
> I am not a programmer, but it would seem to me, that if some bright
> young programmer would be willing to put in slightly more complicated
> algorithm. (Note, we're not going for actual geological accuracy in
> our fractal stuff... just the appearance of realism.) So have some
> 'steeper' gradients, and make them more common than continental
> mountain ranges. When the weathering algorithms are run, don't
> weather things in the same. I know it will take longer to process,
> but some parts of the world go UP while other parts of the world go
> down. There's already a good bit of randomization with the fractal
> coastlines and fractal elevation features and so forth. How much
> harder, from a programing stand point, would it be to set 'weathering'
> to be dependent on how far from a coast line one is? to have the
> program flip a coin periodically to decide "ok this time we're doing
> internal mountains". Note: The Water weathering tends to be much
> less on continental interiors. The bigger the continent, the dryer
> the interior, because the more moisture is likely to be dropped
> somewhere else, before it gets to the interior. Which means on places
> like the great Planes yo get much more wind erosion to water erosion
> than you get in say... Florida. There are exceptions, there are
> always exceptions, but rather than trying to program in all the
> geologic laws, I would like to see some of these features randomized a
> little more. I can figure out a techtonic configuration to make most
> things work, but about 99% of what I saw out of Fractal Terrains and
> about 90% of what I see out of FWE can only be explained in continent
> on continent collisions.
>
> Now that was a longer ramble than I intended, I hope it made sense? I
> can elaborate on any given point.
>
> ~Heather
>
>
>
> On 8/6/07, Mike Oliver <mike-oliver-at-blueyonder.co.uk> wrote:
> > Hi Heather:
> >
> > This should probably go on the CC2 group list but I don't believe you
> > post there.
> >
> > I started using Fractal Terrains to generate all my worlds but have
> > almost abandoned it for very much the reasons you outline. The terrain
> > generated tended always to be coastal lowlands graduating to a central
> > mountain peak - not much in the way of coastal mountain chains and the
> > like (although that may be the way I had set up the generation process).
> > I was just about to give FWE the chance to take over that aspect of my
> > world building but maybe I shall have the same problem.
> >
> > I believe that Joe Slayton, who designed FT, has openly stated that he
> > did not attempt to replicate the effects of continental drift or
> > tectonic plates in the software. However, you say that "continent on
> > continent collision" mountain building is present. It is probably my
> > ignorance but what is the difference between this and continental drift?
> >
> > Cheers,
> >
> > Mike
> > www.cartography-services.co.uk
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