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7 Natural Wonders of the World
New Seven Wonders of Nature-One
of 28 nominees. Winners will be announced in 2011.
The Grand Canyon is
a steep-sided gorge carved by the
Colorado River in the United States
in the state of Arizona. It is largely
contained within the Grand Canyon
National Park, one of the first national
parks in the United States. President
Theodore Roosevelt was a major proponent
of preservation of the Grand Canyon
area, and visited it on numerous occasions
to hunt and enjoy the scenery.
Longstanding scientific consensus
has been that the canyon was created
by the Colorado River over a six million
year period. The canyon is 277 miles
(446 km) long, ranges in width from
4 to 18 miles (6.4 to 29 km) and attains
a depth of over a mile (1.83 km) (6000
feet). Nearly two billion years of
the Earth's geological history have
been exposed as the Colorado River
and its tributaries cut their channels
through layer after layer of rock
while the Colorado Plateau was uplifted.
The "canyon began in the west,
followed by another that formed in
the east. Eventually, the two broke
through and met as a single majestic
rent in the earth some six million
years ago. The merger apparently occurred
where the river today bends to the
west, in the area known as the Kaibab
Arch."
Before European immigration,
the area was inhabited by Native Americans
who built settlements within the canyon
and its many caves. The Pueblo people
considered the Grand Canyon ("Ongtupqa"
in Hopi language) a holy site and
made pilgrimages to it. The first
European known to have viewed the
Grand Canyon was García López
de Cárdenas from Spain, who
arrived in 1540
Geography
Apollo Throne in sunset light from
the South Rim of the Grand Canyon
at Moran Point.The Grand Canyon is
a massive rift in the Colorado Plateau
that exposes uplifted Proterozoic
and Paleozoic strata, and is also
one of the six distinct physiographic
sections of the Colorado Plateau province.
The Grand Canyon is unmatched throughout
the world for the vistas it offers
to visitors on the rim. It is not
the deepest canyon in the world—Cotahuasi
Canyon (11,598 feet or 3,535 m) and
Colca Canyon (10,499 feet or 3,200
m), both in Arequipa, Peru, and Hells
Canyon (7,993 feet or 2,436 m) on
the Oregon-Idaho border, are all deeper,
nor the widest (this is Capertee Valley
in Australia - which is about 1 km
wider and longer than Grand Canyon)—
but the Grand Canyon is known for
its overwhelming size and its intricate
and colorful landscape. Geologically
it is significant because of the thick
sequence of ancient rocks that are
beautifully preserved and exposed
in the walls of the canyon. These
rock layers record much of the early
geologic history of the North American
continent.
Temples, Castles, and Shrines.Uplift
associated with mountain building
events later moved these sediments
thousands of feet upward and created
the Colorado Plateau. The higher elevation
has also resulted in greater precipitation
in the Colorado River drainage area,
but not enough to change the Grand
Canyon area from being semi-arid.
The uplift of the Colorado Plateau
is uneven, and the north-south trending
Kaibab Plateau that Grand Canyon bisects
is over a thousand feet higher at
the North Rim (about 1,000 ft/300
m) than at the South Rim. The fact
that the Colorado River flows in a
curve around the higher North Rim
part of the Kaibab Plateau and closer
to the South Rim part of the plateau
is also explained by this asymmetry.
Ivo Lucchitta of the U.S. Geological
Survey first suggested that, as the
Colorado River developed before significant
erosion of the region, it naturally
found its way across or around the
Kaibab Uplift by following a "racetrack"
path to the south of the highest part
of the plateau. Almost all runoff
from the North Rim (which also gets
more rain and snow) flows toward the
Grand Canyon, while much of the runoff
on the plateau behind the South Rim
flows away from the canyon (following
the general tilt). The result is deeper
and longer tributary washes and canyons
on the north side and shorter and
steeper side canyons on the south
side.
Temperatures on the
North Rim are generally lower than
the South Rim because of the greater
elevation (averaging 8,000 ft/2,438
m above sea level). Heavy rains are
common on both rims during the summer
months. Access to the North Rim via
the primary route leading to the canyon
(State Route 67) is limited during
the winter season due to road closures.
Views from the North Rim tend to give
a better impression of the expanse
of the canyon than those from the
South Rim.
Geology
A sunset on Grand CanyonThe principal
consensus among geologists is that
the Colorado River basin (of which
the Grand Canyon is a part) has developed
in the past 40 million years. A recent
study places the origins of the canyon
beginning some 17 million years ago.
Previous estimates had placed the
age of the canyon at 5 to 6 million
years. The study, which was published
in 2008 in the journal Science utilized
uranium-lead dating to analyze calcite
deposits found on the walls of nine
caves throughout the canyon. There
is a substantial amount of controversy
because this research suggests such
a substantial departure from prior
widely supported scientific consensus.
The result of all this
erosion is one of the most complete
geologic columns on the planet.
The muddy Colorado River from Navajo
Point.The major geologic exposures
in the Grand Canyon range in age from
the 2 billion year old Vishnu Schist
at the bottom of the Inner Gorge to
the 230 million year old Kaibab Limestone
on the Rim. Interestingly, there is
a gap of about one billion years between
the stratum that is about 500 million
years old and the lower level, which
is about 1.5 billion years old. That
indicates a period of erosion between
two periods of deposition.
Many of the formations
were deposited in warm shallow seas,
near-shore environments (such as beaches),
and swamps as the seashore repeatedly
advanced and retreated over the edge
of a proto-North America. Major exceptions
include the Permian Coconino Sandstone,
which most geologists interpret as
an aeolian sand dune deposit and several
parts of the Supai Group.
The great depth of the
Grand Canyon and especially the height
of its strata (most of which formed
below sea level) can be attributed
to 5,000 to 10,000 feet (1500 to 3000
m) of uplift of the Colorado Plateau,
starting about 65 million years ago
(during the Laramide Orogeny). This
uplift has steepened the stream gradient
of the Colorado River and its tributaries,
which in turn has increased their
speed and thus their ability to cut
through rock (see the elevation summary
of the Colorado River for present
conditions).
Weather conditions during
the ice ages also increased the amount
of water in the Colorado River drainage
system. The ancestral Colorado River
responded by cutting its channel faster
and deeper.
The base level and course
of the Colorado River (or its ancestral
equivalent) changed 5.3 million years
ago when the Gulf of California opened
and lowered the river's base level
(its lowest point). This increased
the rate of erosion and cut nearly
all of the Grand Canyon's current
depth by 1.2 million years ago. The
terraced walls of the canyon were
created by differential erosion.
About one million years
ago, volcanic activity (mostly near
the western canyon area) deposited
ash and lava over the area, which
at times completely obstructed the
river. These volcanic rocks are the
youngest in the canyon.[2]
