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!
