#metamorphic rocks

Because there's a LOT to unpack, here, I'm gonna do it in parts, and I'll provide explanations as we go. I'll be tagging all of these posts with "WOCgeology."

One of the big things I want y'all to take away from this is that all rocks on Earth fall into one of three groups depending on how they form: Metamorphic, igneous, and sedimentary.

Metamorphic rocks: Form when a rock is altered by high temperatures, and/or water, and/or high pressures without melting.

Igneous rocks: Form when rock is heated to the point of melting (becomes a liquid) and allowed to cool.

Sedimentary rocks: Form when a rock is broken down chemically or physically (weathered), and the pieces/ions move to a new place (erosion/transportation), stop moving (deposition), and solidify (cementation and/or compaction and/or crystallization--but at temperatures outside of those what would melt or metamorphose)

I'm gonna start with metamorphic because I could only find three examples: The mountains near Thomasville, GA (Cars 3), Gasket Geyser at Piston Peak National Park (Planes Fire and Rescue) and the Himalaya Mountains (Planes). There might be more, but I gotta do a re-watch of all media with my geology lenses on. If I find more, I'll add them to this post and reblog it. :)

The mountains around Thomasville were very clearly modeled after the Great Smokey Mountains, a sub-range within the broader Appalachian Mountain Range. Compare the image below of the GSM in North Carolina to the thumbnail at the top of this post.

Metamorphic rocks need high temperatures and pressures in order to form...and the geologic forces that create non-volcanic mountains are perfect for that.

These are the conditions that we're talking about:

This image above has a lot of stuff going on...but it's got some useful takeaways. First: Metamorphism occurs over a WIDE range of temperatures and pressures. Second: different T and P regimes create different types of metamorphic rock. Third: The parent rocks, themselves, have unique compositions that react to changing T and P in different ways, creating unique mineral assemblages ("facies"). Fourth: Metamorphism has limits. If rock gets too hot, it melts. If it's not hot enough or if the pressures aren't right, the parent rock won't change at all.

So...how do we change T and P?

The Earth's core is hotter than the surface. The rate at which the temperature increases with depth is called the "geothermal gradient." The deeper you go the hotter things get. Pressure, called "lithostatic pressure," also increases with depth. If molten rock or really hot water touches existing rock, the heat from either is enough to alter it (contact and hydrothermal metamorphism, respectively). Geysers, like Gasket Geyser in Piston Peak National Park, are places where hydrothermal metamorphism can occur. Fun fact: the hot water fueling geysers is generally heated by molten rock deep under ground...so it's not all that uncommon for hydrothermal and contact metamorphism to occur in the same area.

But...consider this satellite image of the Appalachian Mountains from space:

How did they get so squiggly when they're solid rock (and were solid even when they were being metamorphosed)?

The Earth's surface consists of large slabs of rock (called "plates") that are in constant motion. They are pushed and pulled by the rocks deeper down. At that depth, the rocks behave more like dense putty (tho not actually liquid) that moves up and down, heated by even hotter rock and metal deeper within the Earth. Wherever this "putty" goes the overlying rocks have no choice but to follow. The chemical composition of the plates varies from place to place, and depending on the type of rock and the way the plates interact along their boundaries, you can get everything from giant mountain ranges (like the Himalayas) to lush, volcanic islands (think Japan).

Nearly a billion years ago, various types of rocks began colliding with the eastern cost of ancient North America, resulting in a series of mountain building events that would go on to create a giant mountain range, stretching from modern Newfoundland in Canada to northern Georgia in the US. The rocks caught up in the middle of these events became warped and twisted forming metamorphic rock. They likely had a "coating" of sedimentary rock, however, once the mountain building processes stopped, water, ice, and gravity began to gnaw away at them, leaving behind their metamorphic skeletons.

You can think of the Himalayas as a newer version of the Appalachians. They're still growing as I write this, as rocks from the Indian Plate are smushed against rocks from the Eurasian Plate. Because the mountain range is so young, the "coating" of non-metamorphic rocks (sedimentary, in this case) is still present along some parts of the range, though they have been tilted and bent.

Real Himalayas

The Himalayas as depicted in "Planes."

The Planes movies landscapes are a LOT more stylized than what we see in the Cars movies. Even so, they definitely captured the look of the range, and there are even places where you can see some layered sedimentary rock (as seen from snow laying in lines along the layers), like you see in the real Himalayas!

One thing I will note, here, is that the Appalachian mountains stop well north of Thomasville, Georgia (Smokey's hometown). In Cars 3, the area around Thomasville is more reminiscent of what you'd see in Kentucky or North Carolina. One of the images below is a screencap from Cars 3, the other is an actual photo taken in Magoffin county, Kentucky; can you tell which is which?

It's clear that they definitely wanted this rural, hilly aesthetic, but official artwork from Cars 3 (the poster below is is hanging up in the Cotter Pin) puts Thomasville in GA and not in NC.

More to come in part 2. :D