Geology Questions

[Durakken]

So I'm thinking of trying to make something that should be fairly easy to make... but I need some questions answered that I can't really find the answer to.

#1. I'm trying to figure out what is a realistic height difference over, say, about a kilometer. Let's say I want to give a numerical value between 1 and 5000 (meters). If Point A = 1000 what is the maximum/minimum change that Point B can be if it's 1km away.

#2. What is the maximum/minimum/average width of rivers?

#3. Assuming the situation in #1, what is the highest and lowest depths in meters that would be realistic given earth-like conditions.

#4. Was the earth of 4 billion years ago smoother than it is now, and by how much?

#5. How much erosion by water is there per year? does it different by height above sea level? How much so?


What I'm thinking is that I can create a point by point height map, and then create some sort of land break algorythm, and then run through a tectonic simulation which pushes up or down the pixels depths whether the masses collide and then after some number of iterations through this fill with "blue" water.

Of course I might not be able to do it due to the fact it might take a lot more processing power than I have but I'll work on it on the side... The Important questions are the first 2, possibly 3, cuz I need to do this on a much smaller scale. without the tectonics.

[waldronate]

Unfortunately, the answer to most of your questions is "It depends". Some good infographics that will help are:

http://statpics.blogspot.com/2014/12...dimension.html shows river flow in North America. It's one of those hand-wavy "average" things, of course.
http://www.ngdc.noaa.gov/mgg/global/...histogram.html shows some Earth altitude summaries based on the ETOPO1 DEM.



#1: effectively 0 (most estuaries) to 900 meters (a sheer granite outcrop like El Capitan in Yosemite) over the course of a kilometer is possible. Generally, the weaker the material, the lower the terrain relief.

#2: 0 to 50 km, depending on season. Some rivers disappear completely at certain times of the year. The Amazon can get to 50km wide or more at its mouth during the rainy season. The closest persistent feature labeled "river" to where I am rarely gets more than 15m wide when it's raining, which would barely qualify as "river" in a lot of places.

#3: The highest and lowest depths are largely a function of the strength of rocks, especially at depth. The strength of rocks is critically dependent on how much water is in them (contrast topography on Venus with that of Earth, for example: http://www.seafriends.org.nz/oceano/ocean28.gif ).

#4: This goes back to strength of rocks. 4 billion years ago, tectonic plates were much smaller due to both hotter underlying rocks and to less fractionation of continental crust from crustal basalts.

#5: The amount of erosion is proportional to the amount of water present, local slope, and material type. More water=more erosion; steeper=faster erosion; softer materials=faster erosion. As clouds move over a mountain range, they lose water (orographic precipitation). As clouds move farther from the source of moisture that formed them, they lose water. Note that local vegetation can act as a source of moisture: it's called the rainforest not just because it receives external moisture, but also because it makes its own rain!

There is a constant interplay of mountain building vs. erosion. An orogeny (mountain building episode) occurs when local conditions cause uplift that's faster than erosion such as at an active convergent plate boundary or hotspot. The newly-uplifted elements are typically sediment-covered and tend to erode at a high rate. As the topography is eroded flatter and/or more resistant rocks emerge, erosion slows. Eventually, in the absence of uplift, everything would be planed down to sea level (check out the life cycle of a coral atoll from volcano to seamount).

[Chick]

4 billion years ago, the Earth was a smaller ball of rock populated primarily by huge volcanoes (think Olympus Mons on Mars). The crust was entirely basalt and there was very little water at all.

[Durakken]

I was looking up stuff about tectonic plates and thought this image and explanation might be useful as it shows how a fracture will form from different types of stress... albeit on bone... Just putting it here cuz don't want to start a new thread and someone might stumble upon it here if they're looking for this info.

fracture-ppt-14-638.jpg