But then I wrote a paragraph or two covering the arrival of humans on Gavanna (yes, they show up. No, they're not native. No, I'm not saying more on the subject right now) and their first impression of the world, and then I felt a burning need to illustrate part of the scene, and then three hours vanished rather alarmingly. So today you'll get a short excerpt that may never find its way into any one of my stories, and a short lecture on the oddities of xenogeology. Onward!
She stumbled out with the others
into the weird violet-red twilight, bulbous grape-like growths sprawling across
the lichin-rimed ground and popping nastily beneath their dazed feet while
tough, ropy vines twisted above, draping them with threads of light. Twin suns were barely visible through
the thick foliage above, one sunlike in size but burning rust-red and the other, about half the size, shining a ferocious, piercing blue. A strange moon was set in the sky above, nearly at the
zenith and half full. It looked
like the good, familiar moon, but swollen to three times its normal size. No craters or mares were visible on its blank, featureless white surface.
It
was the mountains that Estella noticed first, though. There didn’t seem to be any trees at all around her, just
vines thick as pythons writhing their way up into the sky and interweaving
themselves with their neighbors to create an immense, self-supporting
network. This tangled thicket of
vines rose in the distance, flowing up and over great buttes and megaliths as
they crawled their way up the mountains’ flanks. As the mountains slanted
upwards, so did the vines, growing more and more distant until to Estella’s
eyes they were nothing more than a green-brown scum, seeping up a rock face
only to falter and die as the continent’s bones rose higher still through the
cold dry air. Estella craned her
head back, following titanic lodes of rust-red stone upwards until they were
lost in the snowline—and then caught them again as the snow itself disappeared,
driven off at last in the sunblasted, cloudless heights. The naked rock was tinted a delicate
blue, like a full moon seen during daytime, and green foxfire flickered and
danced in the carbon-black shadows of the peaks. Unsteadiness quavered up Estella’s spine, her legs folded,
and she thudded to the ground. For
a moment she was genuinely afraid that if she didn’t grab on to something,
anything, she would go tumbling off over the alien forest, falling sideways for
miles and miles towards those space-scraping monoliths. Their presence redefined down.
Ahem. The picture I drew for this cuts out most of the lower view, so fortunately y'all are spared what would no doubt have been an amusing but ultimately horrifying attempt on my part to draw human figures. I also switched the time a bit to after sunset, largely because I had a perfectly lovely starscape already prepared (it's the background to this blog and the title image, as it happens), and I couldn't resist an opportunity to use it again. I left out the "green foxfire" (St. Elmo's Fire writ large, I was thinking) because I wasn't sure that something of that nature would actually happen. This is my first attempt at drawing detailed mountains, incidentally, and I did it mostly from memory and a vague, fuzzy intuitive sense of what mountains should look like. If any of y'all have any geological knowledge, please try to keep the cringing and the exclamations of righteous indignation to a minimum; it disturbs the other guests.
The mountain range you're seeing here is the backbone of Tregillia, the southern continent of Gavanna--although one could just as well say that it's the peak of the mountain Tregillia itself, as the entire continent is essentially one massive, rising peak. In its lower reaches, the mountain range is not unlike some of Earth's highest ranges, like the Andes or the Himalayas. The Andes were built from the collision of a continental plate with an oceanic plate, and therefore have had relatively little continental rock to work with, while the Himalayas (forged by the collision of India with Asia) were built from the stone of two continents, and are consequently larger (I'm simplifying here, but I believe this is fundamentally correct). The peaks of both ranges are very conventionally mountain-shaped, rough cones and ridges prevented from rising too high to too steeply by the constant grinding of glacial ice carving its way down their slopes. The conventionally mountain-shaped peaks in the foreground of this picture are about the size of those ranges, although rather closer to the Himalayas in elevation.
Things happened differently on Gavanna, however. Tregillia is--or was, the encounter is nearly finished at the time during which my stories are set--the site of a collision between three continental plates, with a central small continent being crushed from both the east and west by two other impinging plates. Continental rock is light, and hard to subduct, and because pressure was being applied from both sides there was simply no room for the plates to spread out. The only way they could go was up, and up they went, to the height of the Himalayan plateau, to the height of the ancient Acadian mountains (the great-grandmothers of our Appalachian mountains), and higher still.
Now, the height of a mountain is constrained by several different forces, all acting to drag it back down to Earth. The first and most obvious is the strength of the rock itself; pile too much stone too high, and eventually it won't be able to hold up under its own weight, and the rock in the very heart of the mountain will crumple and melt, causing the mountain to spread and flatten like an immense mud pie dropped on to a hard surface. No mountains on Earth are high enough for this to be limiting, although the Tregillian range, as I've imagined it, is pushing up against this limit.
A second, related limitation is the strength of the crust beneath the mountain. Pile stone too high, and eventually the planetary crust beneath it will begin to buckle and crack from the sheer strain, causing the mountain to sink down into the ground. Interestingly enough, this has acted as a limiting factor on mountain height in our universe, although not on Earth; the great Martian mountain, Olympus Mons, would be even higher than it already is (and it's three times taller than Everest, so that's saying something) if it hadn't gotten so massive that the crust around it fractured and it sank back into the mantle of Mars. Y'all are familiar with Valles Marineris, the Martian canyon that's deeper and longer than any canyon system in the solar system except for the great Mid-Atlantic Rift on Earth? That wasn't carved by water or lava. Valles Marineris is a crack in Mars' crust, the point where the planet gave way under the colossal stress imposed by Olympus Mons. This limitation, however, only applies to volcanic mountains like Olympus Mons, as they're built of rock that's been vomited up on to the surface of the planet, with nothing but the integrity of the crust to support them. Tectonic mountains like the Himalayas, the Andes, and the Tregillian range are built more along the lines of icebergs, made of rock that's less dense than the rock of the mantle, and thus float on the mantle without putting any particular stress on the crust (downward stress, at least. There's still a lot of lateral stress).
Finally, the third limitation on mountain height (and by far the most important, at least on wet worlds like Earth and Gavanna) is erosion. As mountains grow taller, they grow colder, and snow falls on them more regularly and more deeply--and that means glaciers, grinding and cutting their way through the bones of the mountains in a process that is delightfully referred to as the "Glacial Buzzsaw hypothesis." The higher a mountain gets, the deeper the glaciers cut into its hide, wearing it back down again--at least as long as the mountain stays small enough that snow continues falling.*
But what if it doesn't?
High up in the atmosphere, where the sun beats down unimpeded and the boundary between "air" and "vacuum" begins to get a little wobbly, solid ice begins to become unstable. It doesn't melt--the pressure's far too low for that to happen--but it begins to wear away nonetheless, subliming off into vapor. None of the mountains on Earth are high enough for this process to occur faster than the rate of snowfall, but on Gavanna, that's not the case. The Tregillian range, forced skyward by a tectonic collision far greater than anything Earth has witness in the past 100 million years (I'm not comfortable going further back than that), managed to rise higher than the snowclouds, and once it did the icecaps on its very highest peaks slowly sublimed away into radiation-blasted void. And then...they endured. There was no rain at those heights, no snow, no plant roots or freeze-thaw cycles or even echoing sounds. Just emptiness, and stillness. Far beneath them the glaciers continued to grind away, but not quite as fast as the mountains were rising, and so the titanic monoliths slowly rose up into the sky, huge red-black teeth growing out of a snowy jaw. At the time that my stories are set, they're about as tall as they ever will be; the continents that had been colliding from the east and west have been almost completely consumed, and although the oceanic crust connected to them are still being subducted, the vast sheets of light, buoyant continental crust that had fueled the mountain growth are gone. The Tregillian mountains are now only barely keeping pace with their own erosion, and in a relatively small period of time--ten, twenty million years, shall we say--erosion will gain the upper hand, and will begin eating away at the foundations of the gigantic mountain-pillars. Few, if any, of them will fall; more likely, they'll slowly crumble, mountain-sized sheets of rock flaking off their sides to smash into the glaciers far below. They'll eventually be whittled away entirely, the dust and fragments from their deaths washing down the rivers of Tregillia to be lost in the ocean.
But for now, for a little while longer, they are still mighty.
*Nota bene: The glacial buzzsaw idea that I presented above is very nice and neat and comfortable, but there are actually some very legitimate doubts raised about its accuracy. Evidence has been presented indicating that for some mountains, at least, their sheet of ice can actually act to protect them from erosion, allowing them to attain heights they would otherwise never reach. Be that as it may, though, glaciers obviously do have a erosive effect, and I strongly suspect that if a mountain is better off with an icecap than with exposure to wind and airborne grit, it's even better off if it doesn't have to deal with either ice or wind--as the Tregillian range would be, once it rose above most weather and was able to sublime away its ice layer.
Ahem. The picture I drew for this cuts out most of the lower view, so fortunately y'all are spared what would no doubt have been an amusing but ultimately horrifying attempt on my part to draw human figures. I also switched the time a bit to after sunset, largely because I had a perfectly lovely starscape already prepared (it's the background to this blog and the title image, as it happens), and I couldn't resist an opportunity to use it again. I left out the "green foxfire" (St. Elmo's Fire writ large, I was thinking) because I wasn't sure that something of that nature would actually happen. This is my first attempt at drawing detailed mountains, incidentally, and I did it mostly from memory and a vague, fuzzy intuitive sense of what mountains should look like. If any of y'all have any geological knowledge, please try to keep the cringing and the exclamations of righteous indignation to a minimum; it disturbs the other guests.
Things happened differently on Gavanna, however. Tregillia is--or was, the encounter is nearly finished at the time during which my stories are set--the site of a collision between three continental plates, with a central small continent being crushed from both the east and west by two other impinging plates. Continental rock is light, and hard to subduct, and because pressure was being applied from both sides there was simply no room for the plates to spread out. The only way they could go was up, and up they went, to the height of the Himalayan plateau, to the height of the ancient Acadian mountains (the great-grandmothers of our Appalachian mountains), and higher still.
Now, the height of a mountain is constrained by several different forces, all acting to drag it back down to Earth. The first and most obvious is the strength of the rock itself; pile too much stone too high, and eventually it won't be able to hold up under its own weight, and the rock in the very heart of the mountain will crumple and melt, causing the mountain to spread and flatten like an immense mud pie dropped on to a hard surface. No mountains on Earth are high enough for this to be limiting, although the Tregillian range, as I've imagined it, is pushing up against this limit.
A second, related limitation is the strength of the crust beneath the mountain. Pile stone too high, and eventually the planetary crust beneath it will begin to buckle and crack from the sheer strain, causing the mountain to sink down into the ground. Interestingly enough, this has acted as a limiting factor on mountain height in our universe, although not on Earth; the great Martian mountain, Olympus Mons, would be even higher than it already is (and it's three times taller than Everest, so that's saying something) if it hadn't gotten so massive that the crust around it fractured and it sank back into the mantle of Mars. Y'all are familiar with Valles Marineris, the Martian canyon that's deeper and longer than any canyon system in the solar system except for the great Mid-Atlantic Rift on Earth? That wasn't carved by water or lava. Valles Marineris is a crack in Mars' crust, the point where the planet gave way under the colossal stress imposed by Olympus Mons. This limitation, however, only applies to volcanic mountains like Olympus Mons, as they're built of rock that's been vomited up on to the surface of the planet, with nothing but the integrity of the crust to support them. Tectonic mountains like the Himalayas, the Andes, and the Tregillian range are built more along the lines of icebergs, made of rock that's less dense than the rock of the mantle, and thus float on the mantle without putting any particular stress on the crust (downward stress, at least. There's still a lot of lateral stress).
Finally, the third limitation on mountain height (and by far the most important, at least on wet worlds like Earth and Gavanna) is erosion. As mountains grow taller, they grow colder, and snow falls on them more regularly and more deeply--and that means glaciers, grinding and cutting their way through the bones of the mountains in a process that is delightfully referred to as the "Glacial Buzzsaw hypothesis." The higher a mountain gets, the deeper the glaciers cut into its hide, wearing it back down again--at least as long as the mountain stays small enough that snow continues falling.*
But what if it doesn't?
High up in the atmosphere, where the sun beats down unimpeded and the boundary between "air" and "vacuum" begins to get a little wobbly, solid ice begins to become unstable. It doesn't melt--the pressure's far too low for that to happen--but it begins to wear away nonetheless, subliming off into vapor. None of the mountains on Earth are high enough for this process to occur faster than the rate of snowfall, but on Gavanna, that's not the case. The Tregillian range, forced skyward by a tectonic collision far greater than anything Earth has witness in the past 100 million years (I'm not comfortable going further back than that), managed to rise higher than the snowclouds, and once it did the icecaps on its very highest peaks slowly sublimed away into radiation-blasted void. And then...they endured. There was no rain at those heights, no snow, no plant roots or freeze-thaw cycles or even echoing sounds. Just emptiness, and stillness. Far beneath them the glaciers continued to grind away, but not quite as fast as the mountains were rising, and so the titanic monoliths slowly rose up into the sky, huge red-black teeth growing out of a snowy jaw. At the time that my stories are set, they're about as tall as they ever will be; the continents that had been colliding from the east and west have been almost completely consumed, and although the oceanic crust connected to them are still being subducted, the vast sheets of light, buoyant continental crust that had fueled the mountain growth are gone. The Tregillian mountains are now only barely keeping pace with their own erosion, and in a relatively small period of time--ten, twenty million years, shall we say--erosion will gain the upper hand, and will begin eating away at the foundations of the gigantic mountain-pillars. Few, if any, of them will fall; more likely, they'll slowly crumble, mountain-sized sheets of rock flaking off their sides to smash into the glaciers far below. They'll eventually be whittled away entirely, the dust and fragments from their deaths washing down the rivers of Tregillia to be lost in the ocean.
But for now, for a little while longer, they are still mighty.
*Nota bene: The glacial buzzsaw idea that I presented above is very nice and neat and comfortable, but there are actually some very legitimate doubts raised about its accuracy. Evidence has been presented indicating that for some mountains, at least, their sheet of ice can actually act to protect them from erosion, allowing them to attain heights they would otherwise never reach. Be that as it may, though, glaciers obviously do have a erosive effect, and I strongly suspect that if a mountain is better off with an icecap than with exposure to wind and airborne grit, it's even better off if it doesn't have to deal with either ice or wind--as the Tregillian range would be, once it rose above most weather and was able to sublime away its ice layer.
This is a mighty impressive world you've got going here, Ronan. I hope that more development of this happens, I really do.
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