Complete Question:
Dr. Alley once helped a Grand Canyon ranger answer a tourist’s question: "Why is the Canyon wider at the top than at the bottom?" The tourist had their own favorite theory. Based on the materials that have been presented to you’ve in this class, what geologically accepted answer would Dr. Alley and the ranger have given the tourist?
A) The river cuts down, and that steepens the walls of the canyon, which fall, topple, slump, creep or flow into the river to be washed away, thus widening the canyon above the river.
B) The canyon is really the same width at the top as at the bottom, but the well-known "optical illusion" of distant things appearing smaller causes it to look as if the canyon is narrowing downward.
C) The bulldozer that made the canyon was wearing out its blade as it dug down.
D) The river used to be much wider because it was not steep, and water spreads out when running slowly (a little tap feeds a big bathtub...); then, as the Rockies were raised, the river steepened and narrowed, so it used to cut a wide canyon and now cuts a narrow one.
E) The river used to be much wider before the desert formed, and so cut a wide canyon, but the river has narrowed as the drying occurred, and now cuts only a narrow canyon
According to Wikipedia, Grand Canyon is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is 277 miles (446 km) long, up to 18 miles (29 km) wide and attains a depth of over a mile (6,093 feet or 1,857 meters).
Grand Canyon is part of the Colorado River Basin,it has layered bands of red rock revealing millions of years of geological history.It towering cliff was craved by the copper-colored Colorado River and its tributaries cut their channels through layer after layer of rock while the Colorado Plateau was uplifted.
The Canyon is wider at the top than at the bottom because the river (Colorado River and its tributaries) cuts down, and that steepens the walls of the canyon, which fall, topple, slump, creep or flow into the river to be washed away, thus widening the canyon above the river.
