I haven't read most of the posts in this thread, so I apologize if I restate or resurrect
an old topic. But anyway, I guess I'll share whatever I know. Not much. I'll start
with plate tectonics;
--On a collision boundary between two land plates, there are mountains; the crust has
nowhere to go but up.
--On a diverging boundary, shield volcanos (gentle) raise up. Check out the Mid-Atlantic
Ridge - Wikipedia, the free encyclopedia for an underwater example, as well.
-- On a collision boundary between two land plates, one ocean crust is pushed under the
other. The rock and water trapped under plate #2 fuels the creation of magma. On this
boundary you have cone volcanoes (active) and a trench (located where one plate goes
under the other).
--On a collision boundary between one land mass and one ocean, you'll find an off-shore
trench and cone volcanoes.
--On a sliding boundary, where one plate is going past the other, you'll have a fault.
--Note that earthquakes (and, when underwater boundaries are involved, Tsunamis) will
occur at many plate boundaries. An island chain is formed by the movement of a hot-spot
(mantle plume) moving with the plate. Bigger islands are newer because they have not
yet been subject to weathering.
--Finally, I think most cartographers know about puzzle fit. When two plates with land
pull apart, it looks like they could go back together.
Some of this might apply to the map you posted in the introductory post to this thread.
I'd also like to add that a lot of the features and their locations will be in correspondence
to the other features. A valley might have lush forest due to a water-shed. All the rivers
coming down and washing the soil out from the mountains will create good soil for
growing (not to mention, trees need water). Plus, mountains can create rain on one side
(I'm thinking of Seattle and the West Coast of South America) So, following my logic, I'd
imagine the mountains would be surrounded by forests and rivers. Your rivers looked to
comply with "science" well.
What I'd be interested to learn about would be lakes. I live near a lake and enjoy doing
so, but I don't see why a lake would form. That's cartography "science" I don't understand.
Any ideas? Best of luck, I know everyone here tries to be really informative.
Thanks ! :)
I've been trying to read up on tectonics and I kind of get the idea... your restatement of the effects clarified a lot. What I really don't understand is WHY they would move against another plate instead of into it, or away from it... like... how does it shift one direction instead of the other?
Oooo lakes are easy... and weird.
Originally Posted by foremost
there's a couple of different ways a lake can form.
If you have a depression in the ground (think of a bowl, or a saucer) and you have a TON of rain in that area, the depression will fill. It has to be a LOT of rain to make this a lake (or even a pond) because most of the water will be absorbed, eventually, into the ground. Because of this, sometimes a lake will form, and if there isn't enough precipitation, it will dry up, because more water will be absorbed than added. :) (Think of puddles after a heavy shower.. they pool wherever the ground is lowest.)
This will also happen with other sources of water - like rivers - anywhere there is LOWER ground, and more water than can be absorbed/diverted, the water will pool.
So lakes might be more frequent where 2 rivers meet in a low-lying area than a single river, because there's more water now, and more force behind it.
But you also need that depression in the ground :)
Water flows down, so if there's lower ground than the lake-area, the water is going to leave that way. If there's too *much* lower ground, ALL the water will leave, and you won't have a lake at all. If there isn't *enough* lower ground, the water level will keep rising. The lake will get bigger, and cover more/higher area. Eventually it will find a lower path to take. Water will flow out of the first lower area it finds, which is why USUALLY there's only 1 river leading out of a lake, and almost all lakes have a river leading out.
If a lake does not have a river leading out, either it finds an exit for the water underground, or the water is absorbed and it dries up.
Another way a lake can form is from flooding. This is pretty much the same thing as your "ice melt" lakes. When, say, a river floods, it covers land that isn't usually in its' path. Sometimes it fills depressions in the ground that were dry ground before. As the thin layer of water on the higher ground is absorbed, there's still water in the depression. (think of puddles - the smaller ones disappear first.)
The water in the depression is sometimes absorbed, but some of it evaporates, causing more rainfall, and cycles the water back into the new-formed lake.
There's also water under the ground. (More than most people think). Sometimes, the force of the water pushes it up through the ground, like lava from a volcano. This could evaporate or be absorbed, but usually it turns into springs, or pools into lakes. :)
Sometimes... there's these certain types of volcanos that EXPLODE ... literally explode... no more volcano. no more anything-that-was-around-the-volcano. just a huge (disturbingly round) pit in the ground. The water outside the "blast radius" is still flowing like it normally would, but now, instead of running over land, it finds this huge hollow and fills it. :)
Of course all of this is the highly-simplified, not strictly accurate/scientific explanation, but it is, in essence, why lakes *usually* form. There are lots of other ways too, though :)
I'm sure someone will come along and explain it better, but those are the basics :P
Originally Posted by Jalyha
Almost every plate will have a boundary where it is being subducted and one opposite where it is getting "on top" or where new oceanic crust is being formed. They will move towards the subducted area, this is because of three reasons:
- extra weight from rising mountains will make it slide away from that point
- the subducted part will sink into the mantle before completely detaching from the rest of the plate, sucking it in a "pull" force towards the boundary.t
- there is movement in the molten mantle, which also carries the floating plates on top of it; that movement is a cell where hot magma rises in the ridge area, spreads out and sinks again a little colder somewhere else (just like hot water rising from the bottom of a pan).
So, the way you start with tectonics on a map (from personal experience) is to define major oceanic ridges and rough limits of those plates and make them move away from those ridges. If you already have the continents and the oceans, keep experimenting where ridges make sense - not all oceans need to have active ridges, but most will, and ridges do not have to be in the center of the ocean (doesn't happen in the Pacific, for example)
One other point:
- smaller plates also rotate. Actually, all plates may have rotation movement, but in smaller ones it can be very pronounced. The Arabian plate, rotating anti-clockwise is a good example. We tend to forget the smaller plates when "imagining" a world, but they come really handy to "round the corners".
This pretty simple image shows how the bulk of tectonics comes from movement started in the oceanic ridges.
omg thank you!
That's awesome. Exactly what I was trying to find out ^_^ I'mma go push my world around :twisted:
Just wanted to add something:
Plates move because of convection currents. The half-molten rock
that's part of the Earth's crust is always heating and cooling (thus
rising and falling, think of a lava lamp). It generates plate
Thicker continental crusts will run right over the ocean crusts,
cause those are generally thinner. The submerged rock combines
with water (gets sucked down as well) and forms lava. Lava rises
via a cone volcano.