Located within northern Arizona is one of the planet's most impressive geologic wonders.
There, the Colorado River cuts deep into the sedimentary rocks of the Grand Canyon, exposing
near horizontal layers which are a wide assortment of colors ranging from orangish red to white.
Here, 1.8 billion years of geology spread across more than 6,000 feet or 1800 meters
of rock are exposed for the eye to see.
All of this was carved by the erosion of water over millions of years, forming a truly unique
geologic landmark.
However, despite being one of the most visited tourist attractions in the United States,
there are many things about the Grand Canyon which people do not know.
For example, the Grand Canyon contains an active volcano called the Uinkaret volcanic
field, which last erupted a mere 900 years ago, and even erupted lava into the literal
middle of the Grand Canyon.
Also, within the Grand Canyon is a prominent feature referred to as the "Great Unconformity"
where nearly 1.2 billion years of deposited rock is seemingly missing.
This unconformity is widely seen across the American Southwest, where there is an aprupt
gap in rocks dated between 1.7 billion and 545 million years ago.
The "missing" rock did exist at one point, but was carved away during a period of thick
glaciation around the planet, thus removing it from the geologic record.
The vast Grand Canyon stretches for 277 miles long, and is up to 18 miles wide.
You might think that given its depth which is more than a mile in some locations that
the canyon was carved over hundreds of millions of years.
However, this is not the case.
The Grand Canyon is quite a young geologic feature which began forming a mere 6 million
years ago.
The beginning of the canyon was marked by the creation of the large Colorado River in
the distant Rocky Mountains several hundred miles to the northeast.
There, the high terrain was the site of abundant precipitation.
This water from rainfall and snowfall eventually traveled downhill to the west into a large
river basin, where given enough time, all precipitation across a vast area would end
up in the same location; the Colorado River.
After travelling several hundred miles, waters from the early Colorado River encountered
a vast landscape filled with soft and easily eroded sedimentary rock, mainly a 270 million
year old layer of limestone known as the Kaibab Limestone.
Over time, this undulating river which had a comparatively high speed carved away at
the rock, creating a deep canyon.
Eventually, the canyon became deep enough that secondary side canyons began to form,
which further carved away at the landscape.
1 million years into the formation of the Grand Canyon, it was already uniformly about
150 meters or 490 feet deep.
This high rate of erosion was made possible in part by the relatively steep decline of
the overall river, which lost 7 feet in elevation for every mile it travelled.
Over time, the Colorado River and its side canyons carved deeper into the rock, occasionally
causing undulations which left behind prominent "islands" aka isolated high points in the
overall landscape.
You might be wondering why this high level of erosion simply did not continue indefinitely
into the Sea of Cortez.
The reason is that the soft rocks which made possible deep canyon formation only existed
as exposed rock in a large uplifted area referred to as the Colorado Plateau.
This uplifted area ends near the western edge of Arizona, which is also where the Grand
Canyon ends.
As for the start of the Grand Canyon, it begins at the northernmost surface exposure of the
brittle Kaibab Limestone along the overall Colorado River.
After millions of years of continued erosion, fresh volcanic activity began near the northern
rim of the Grand Canyon, beginning 3.6 million years ago.
Volcanic activity built cinder and spatter cones out of basaltic lava, which occasionally
produced lava flows which flowed into the Grand Canyon.
Between 725,000 and 50,000 years ago, these continued eruptions produced large enough
volumes of lava that it temporarily filled a section of the Grand Canyon, damming the
overall river.
These dams eventually burst, the most recent of which led to the creation of the famed
Lava Falls rapids.
Overall, the volcanic eruptions from this field are relatively infrequent, and pale
in comparison to the power of erosion caused by millions of years of flowing water.
Thanks for watching!
If you would like to request a specific topic, please leave a comment below.
Additionally, I would like to thank my patron Ilisa T for increasing their support tier
on this channel's patreon!