GPH 112 43 Why the Grand Canyon is Grand Stage C.Question 1
2 / 2 pts
How fast is the Grand Canyon widening? (or, what is the
rate of cliff retreat?)
... [Show More] Please use these places in the
geovisualization. Remember, you will be measuring
distances between the North Rim and the Colorado River,
and then the South Rim and the Colorado River to be able
to calculate rates.
Please calculate your answer in centimeters per century
years (cm/century).
Tiyo Point on the North Rim: 36.1806, -112.1278
&
Colorado River between: 36.1055, -112.1562
&
Hopi Point on the South Rim: 36.0733, -112.1551
Correct!
The north side of the Colorado River (from Tiyo Point) is
widening at a rate of about 18 cm/century. The south side
of the Colorado River (from Hopi Point) is widening at a
rate about 7cm/century.
None of the answers listed are even close. Thus, this is
the best answer.
The north side of the Colorado River (from Tiyo Point) is
widening at a rate of about 1.8 centimeters per thousand
years. The south side of the Colorado River (from Hopi
Point) is widening at a rate about 1 cm per thousand years
The north side of the Colorado River (from Tiyo Point) has
widened at a rate of 1.8 meters per million years, while the
south side (from Hopi Point) is widening at 1.2 meters per
million years.
Believe it or not, there’s only one other sort of
study on rates of canyon widening in the heart of the
Grand Canyon. In the Grand Canyon, researchers Ken
Cole and Layer Mayer used packrat midden nests to
estimate rates of cliff retreat using radiocarbon dates on
the middens (that date back a few tens of thousands of
years) to be about 4.5 cm/century. Although this rate is
less, its in the same “ballpark” or order of magnitude.
Question 2
0 / 1.5 pts
How wide would the canyon be (between some future
Tiyo and Hopi Points) 10 million years from now, using
the rate you established in the example given in the
PD file? The correct answer will be in miles, since most
people understand miles at an intuitive level.
About 31.5 miles
You Answered
About 18 miles
About 10 miles
Correct Answer
About 23 miles
What you measured for distances from Tiyo and
Hopi points to the Colorado River will be different from
what we measured. If you got anywhere closed 8700
meters from Tiyo Point and 3500 meters from Hopi Point
(to the Colorado River), then this is how you should have
done the calculations.
Any measurement around 8700 meters from Tiyo
Point to the Colorado River will convert to 1800 meters per
million years. Thus, in 10 million years, the retreat of the
rim would be 18,000 meters.
Any measurement close to 3500 meters from Hopi
Point to the Colorado River will lead you to a bit more than
700 meters per million years when you divide the distance
by 4.8 million years. This rounded off rate of 700 m/Ma will
be multiplied by 10 (million years) giving you a distance of
7000 meters.
Thus, in 14.8 million years, the width of the canyon
would be:
8700 m + 3500 m + 18000 m + 7000 m
or
Tiyo-Colorado distance + Hopi-Colorado
distance + 10 million Tiyo-Colo + 10 million HopiColo
The predicted distance in 10 million years from
now would be about 37,200 meters or 37.2 kilometers.
Since 1 kilometer = 0.6214 miles, the best answer would
be 23.36 miles, rounded off to 23 miles.
Question 3
1.5 / 1.5 pts
How fast did the Colorado River incise down into the
Grand Canyon between 4.8 and 1.2 million years ago
(or over a 3.6 million year period)? The answer should
be in centimeters per century and be calculated for both
Point Sublime on the North Rim and an unnamed point [Show Less]