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On an Earth-like planet, there is a massive plateau, standing more than 1km high, and the breadth of a continent in the middle of an otherwise ocean planet.

I know there are climactic issues to this, but instead of hand-waving it, the best answer would explain the processes that created this steep, high continental mass. High-level, and not magic and no humans.

On the continent (size of, say, Africa) is most biomes - desert, forest, lakes, rivers sourced by artesian springs/rain, and then cascade off the sides of the continent. There are plants and animals.

This is for a young adult novel, so I am not using the hard-science tag.

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    $\begingroup$ So, this is a continent, like Australia, but with no mountains? And seawalls all the way around? $\endgroup$ – Samuel Dec 17 '15 at 21:45
  • $\begingroup$ Massive tectonic plate activity in the past combined with a core of very hard rock and softer stuff around it which corroded/broke away to leave only sheer rock $\endgroup$ – AndreiROM Dec 17 '15 at 21:53
  • $\begingroup$ @Samuel - precisely; there are some mountains but the significant difference is that it is a sheer ~1km cliff drop from the continent to the ocean. No humans. $\endgroup$ – Mikey Dec 17 '15 at 22:23
  • $\begingroup$ How old of a planet are you looking for? Could it have had other continents now past? $\endgroup$ – The Nate Dec 18 '15 at 16:58
  • $\begingroup$ @TheNate - I'm not fussed about age, but I suspect it would be older than our Earth. I'm open to any interpretation, though. $\endgroup$ – Mikey Mar 22 '16 at 0:12
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Massive glaciation

Most continents are already shaped somewhat like plateaus. They slope gently towards the continental margins, before fairly abruptly dropping down to the ocean floor. In profile, they look something like this:

enter image description here

The issue is that most of that plateau-like shape is hidden by water. However, if you get rid of a lot of that water, your continent will start to look more plateau-like.

Massive glaciation would help achieve this. If a significant portion of the planet's oceans are bound up in glaciers, the corresponding lowering of sea levels will make your continents more plateau like. Planets which previously had a steep continental slope with little to no continental shelf will appear as plateaus sticking out of the ocean. Africa is an example of a continent that would appear more plateau-like in this case, while the west coast of South America would also appear to rise sharply out of the ocean.

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  • $\begingroup$ This is a good idea, but with only one continent the size of Africa, the only place the glaciation could go would be on that continent itself. The continent would have to be covered with ice roughly 20 km thick in order to be raised 1 km above sea level. $\endgroup$ – user16107 Dec 18 '15 at 14:37
  • $\begingroup$ Good point, I had missed the whole 'there is only one continent' bit. Unless there exist ice caps that rest on bedrock, this won't work (Unless the continent is reaaaaaaly snowy.). $\endgroup$ – ckersch Dec 18 '15 at 21:40
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A super-massive pumice raft.

Created by continual ocean-based volcanic activity, you could have an increasingly large floating island forming, especially if your planetary ocean did not have significant tidal/current action to shift the raft around.

This might be the most feasible on a planet with low gravity; not sure you could get it more than 1 km high otherwise -- you're dealing with displacement vs. mass physics at that point. The density of the pumice would also be a factor in how buoyant it is. Pumice rafts reported from 2012 volcanic eruptions were reported to be ~300 miles long & ~30 miles wide, but only riding about 2 feet from the surface.

As per my other answer, given enough time and initial planetary biodiversity, the pumice raft would hopefully be seeded with life.

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Conan Doyle used real-world tepuis for his Lost World story, and though the Earth ones aren't as much surface area as you're looking for, the geology and height otherwise seem about right:

Roraima, apprently?

http://www.amusingplanet.com/2013/05/tabletop-mountains-or-tepuis-of.html https://en.wikipedia.org/wiki/Tepui

Though they're lofted from jungles rather than from the sea floor, it might not be too much of a stretch to theorize some swift climate shifting to submerge a lowland with these features, and they definitely fit your 1k height requirement. The morphology section of the Wikipedia link should give you enough research information to extrapolate your version, I think?

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From Wikipedia on how plateaus are formed:

Plateaus can be formed by a number of processes, including upwelling of volcanic magma, extrusion of lava, and erosion by water and glaciers. Magma rises from the mantle causing the ground to swell upward, in really large, flat areas of rock that are uplifted. Plateaus can also be built up by lava spreading outward from cracks and weak areas in the crust. Plateaus can also be formed by the erosional processes of glaciers on mountain ranges, leaving them sitting between the mountain ranges. Water can also erode mountains and other landforms down into plateaus. Computer modeling studies suggest that high plateaus may also be partially a result from the feedback between tectonic deformation and dry climatic conditions created at the lee side of growing orogens.

I don't see any particular reason why these natural processes could not produce a continent as you describe--especially if the right combination of plate tectonics and volcanic activity occurred.

There are already quite large plateaus in the world: the Tibetan Plateau is about 2,500,000 square kilometers (about 1/12 the size of Africa) and is 4.5 times higher above sea level, on average, than your mythical continent.

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A massive large igneous province. the Columbia plateau is one example of such a thing, probably caused by hotspot as opposed to continental rifting, then glaciation. not perfect, but as close as I could surmise.

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The low-velocity impact of a large asteroid in the distant past.

The feasibility of this would heavily depend on physics dealing with the size of the asteroid & its speed, as well as the depth of the planet's oceans.

  • Too fast? -- It would break up into a bunch of small pieces upon impact.
  • Too large? -- It'd possibly vaporize most of the ocean or break the planet itself into pieces.
  • Ocean too deep? -- It wouldn't stick up out of the ocean far enough.

Given enough time and initial planetary biodiversity, the barren asteroid could be seeded with the biomes you describe.

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    $\begingroup$ this is more of a comment than an answer. You should flesh it out. $\endgroup$ – AndreiROM Dec 17 '15 at 21:53
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    $\begingroup$ More like the landing of a very large asteroid, yeah? $\endgroup$ – Samuel Dec 17 '15 at 21:53
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    $\begingroup$ This would most likely just create a really big crater, no? Think about the Chicxulub crater. That was an ocean impact, and look at the effects it caused. Anything big enough to stick out would absolutely cause chaos in the planet. I don't think it would work. $\endgroup$ – HDE 226868 Dec 17 '15 at 22:02
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    $\begingroup$ Anything hitting the Earth from outside of Earth's orbit will be moving at least the Earth's escape velocity when it hits the atmosphere (unless it's powered). That's 11.2 km/s. That will cause quite the dent. $\endgroup$ – Joe Bloggs Dec 18 '15 at 10:00
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    $\begingroup$ @JoeBloggs why is that? Should it not be possible for it to travel at little more than the speed the earth orbits the sun? Then this delta-v would be the impact velocity, would it not? (some gravitational acceleration will be added, but will that be that much?) $\endgroup$ – Burki Dec 18 '15 at 14:58
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Have a smallish tectonic plate, with two massive plates moving towards and sliding under it, one from each side.

The approaching plates would combine to lift up the central smaller one. You'd end up with a lot of volcanic activity and mountain-forming at each join and the smaller plate potentially hoisted right out of the ocean as the other two went under it.

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