[nbos] [FWE][FM8]Geology in the Fractal World

[Doug Jessee]

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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