I'm gonna talk about a really, really cool lake, but first, some geology lessons.
On Earth, mountains and valleys tend to be formed by tectonic motions or volcanism, and then shaped by erosion (mostly water and wind erosion) back into their lowest possible forms. This is why the Appalachians are so much more rounded than other, spikier and younger mountain chains...
On Mars, there is some evidence of that process having taken place as well, but mostly only in the distant past. On Mars, there is a very weak atmosphere which can't really do much to erode away mountains or craters, and so they stay, but the tallest mountains, they tend to flatten out just to the force of gravity.
Take the Alba Mons and Olympus Mons for instance, Alba Mons is a much older volcano, and it has been stretched out by gravity, trying to deform the planet back into a sphere, but Olympus Mons is younger, and that process has only just begun for it.
The stresses of weight of Alba Mons on the surrounding lands has caused a series of striking tectonic features, huge rifts where tectonic pressure has deformed the land. Olympus Mons hasn't yet deformed to the same extent that Alba Mons has, but all of the mass of the Tharsis igneous provinces are being deformed in this way.
The Himalayas and highlands of Asia, likewise, is a very high up region with a lot of mass causing some strain gravitationally, but more than that, on Earth, there's tectonic plates. Huge slabs of crust that tend to move together, one of these places is where Asia is tearing itself apart, this is a place that's home to the world's deepest freshwater lake, a lake so big that it's about the same size as all the Great Lakes combined...
I'm talking of course, about the Baikal Rift Zone in Siberia. Lake Baikal is located where the Eurasian Plate and the Amur Plate have begun to diverge, and a massive, deep rift in the Earth has long since been filled by water.
Is Eurasia tearing itself apart because the continent is too heavy? Probably not, continents generally make up their height by being less dense than ocean crust, but even so they are still heavier than the surrounding regions. Perhaps this a factor in why plates move? Convection of heated rock in the mantle is also a huge factor, and so too is erosion and all those Earthly things, but gravitational deformation is also at play. And as we can see, on Mars it has had a big part in shaping the way that planet is well, shaped. But enough about tectonic stress, let's talk about this funky, tectonically created, deep lake.
They've had a looong time to adapt to these conditions, too. The Great Lakes, which themselves are home to many species of animals which call them home, are only 20,000 years old.
Baikal is at least 25 million years old, by comparison. In its deepest depths it's got some actual hydrothermal vents because of the tectonic activity, and it is the only freshwater lake in the world to have these. Living in these vents are a variety of endemic species which live entirely without need for the light of the sun. Like the freaky depths of the ocean, but like, in a single lake. Weird looking sponges, mats of bacteria, and even some funky freshwater amphipods which are all endemic to Baikal all rely on these vents.
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