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I'd like to construct a planet where the rivers all run east to west, but I need a plausible reason for them to do so.

Rivers run from high altitude to low, but also I suppose there is the coriolis force to push them clockwise or anticlockwise.

Could a glancing blow from a meteor on a south-north vector create both a single dry continent and a series of ridges which run east-west? Possibly combined with a tectonic plate movement to raise one side of the ridges?

Otherwise I'm facing explaining a single triangular continent with a hugely high mountain which has a cliff on the other side, or the same shape for each of a large number of lopsided islands.

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  • $\begingroup$ Are you willing to accept local areas where the rivers run west to east (as the river meanders), as long as eventually all rivers go east -> west? $\endgroup$ Mar 4 '15 at 16:58
  • $\begingroup$ Yes, that's fine. $\endgroup$
    – Phil H
    Mar 4 '15 at 17:07
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In prehistoric times the planet lost a large amount of volume from its magma mantle. Maybe it was a really fast-moving, tiny black hole that "flew through" pulling a lot of matter with it. Maybe a huge gas pocket broke free. Anyway, the planet got smaller, losing some mass from the inside.

The effect is dual: the tectonic plates are suddenly too large and overlap over the reduced size of the mantle; and the rotary speed of the planet changes rapidly, making the plates "float" in one direction. And in effect, they stack like scales on a Roly-Poly. Currently, each tectonic plate forms a huge mountain range on the East, and is submerged in the ocean from roughly the middle of its width, the western end sliding under the next plate. All of them are tilted east-to-west, and the tall mountain ranges may only have some short, rapid streams on their eastern sides, while all large rivers flow down the slope, towards the west. They may curve and stray a little north or south, but the general sloping of all tectonic plates simply overcomes all lesser factors that could affect their direction.

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  • $\begingroup$ I like this one the most out of all the answers because it makes the most sense =D $\endgroup$
    – Aify
    Mar 4 '15 at 20:15
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A long escarpment is a perfectly normal geological feature here on Earth without the need for a meteor, and in fact plate tectonics can also raise parallel ridges like this.

All your model would require is a a tectonic plate edge with a sufficiently straight north-south section where the plate moving eastwards floats up on top of the plate moving westwards. This can give you a very steep eastern slope or cliff down to sea, with a longer, more gentle western slope.

Combine this with a wind from the west and if your ridge is high enough you will have all your rainfall on the west side of the ridge, as happens on the west side of the Andes, and consequently rivers running from there westwards.

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    $\begingroup$ Ok, but a whole world like this? Unless it has one tiny continent constructed as you describe, it would have to be 'chance' that all the continents have the same structure. $\endgroup$
    – Phil H
    Mar 4 '15 at 11:41
  • $\begingroup$ That's a good point Phil - I hadn't fully grokked that part of the question. $\endgroup$
    – Rory Alsop
    Mar 4 '15 at 12:21
  • $\begingroup$ Wouldn't work, as some moisture would inevitably make it over the ridgeline. If you look at Earthly formations, like the Sierra Nevada, you see much more water flowing west, but you still have rivers - the Truckee, Carson, Walker, & many smaller streams - that flow down the east slope. $\endgroup$
    – jamesqf
    Mar 4 '15 at 20:30
  • $\begingroup$ Jamesqf - look at the rain shadow from the Andes. There are vast swathes that have no moisture on the east side. That rain shadow even covers parts of the Falklands. It's an easy step to delivering this. Phil has a valid point though. $\endgroup$
    – Rory Alsop
    Mar 4 '15 at 20:33
  • $\begingroup$ @Rory Alsop: Vast swathes that have no moisture on the east side. Like the Amazon Basin? And note that a lot of this depends on prevailing winds, which change direction with latitude - Amazon gets moisture from NE trade winds with Atatcama desert on the west side, further south westerlies dump moisture on Chile, leaving the Argentine pampas dry. $\endgroup$
    – jamesqf
    Mar 5 '15 at 3:43
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This may not be exactly what you are looking for, but I think it gets sort of close and it’s certainly interesting. If your planet was a moon and orbited closely around a much larger body then tidal effects could explain all of your water flowing in one direction.

Tides on Earth are quite complex. They are a result of the gravitational influence of the Sun and the Moon on the Earth. To put it simply, when one of these bodies is directly overhead, the gravity a person (or a body of water) feels is slightly reduced because the overhead mass exerts a slight pull towards it. This results in a high tide in our oceans because they are large fluid bodies that can react to these subtle forces very noticeably. There is also a high tide on the opposite side of the planet at the same time as a result of the rotational mechanics. This is not intended to be anything close to a good explanation for how tides work, but it will suffice for my suggestion.

If your planet is orbiting closely around a large planet it will have much larger tidal effects than we do on Earth. If your planet spins toward the East, like the Earth does, then the side of your planet facing the other large body will move West, much like the side of the Earth facing the Sun moves West. With exaggerated tides this could cause much of the water on your planet to “flow” West, to continue facing the large body your planet is orbiting. Essentially the large body would exert a pull on the majority of the water on your planet in a Westward direction.

What affects millions of years of these tides would have on the formation of the rivers and lakes and oceans I really can’t say. But it seems possible to me that it would result in the majority of the planet’s major rivers flowing West and carving out large valleys that have large diurnal tides.

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  • $\begingroup$ I like this approach, particularly because it ties some interesting physics to a bit of astronomy - the view in the sky would be dominated by the gas giant being orbited. $\endgroup$
    – Phil H
    Mar 4 '15 at 17:09
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Definition of the planet is that forms itself to round shape under own gravity. This applies also to tectonic plates (if they float over melted mantle). Random forces would unlikely result in any shape you can use.

But do not despair: Your best bet would be to have such planet build by advanced civilization. We already had cube-shaped planet and torus-shaped planet. We could have also one with vertical cliffs on east side of the mountains and gradual to the west. For a graduate degree in planet design.

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