Horseshoe Bend
An alternate fisheye lens view of the Colorado River in the Horseshoe Bend, Page, Arizona
Horseshoe Bend is a superb example of an entrenched meander. Six million years ago, the region around Horseshoe Bend was much closer to sea level, and the Colorado River was a meandering river with a nearly level floodplain. Between six and five million years ago, the region began to be uplifted. This trapped the Colorado River in its bed, and the river rapidly cut downwards to produce Horseshoe Bend as we see it today.
The cause of this uplift is still a matter of research. One hypothesis is that uplift was a result of delamination, where the lowest layer of the North American tectonic plate below the Colorado Plateau detached and sank into the underlying mantle. This would have allowed hotter rock from the asthenosphere, the part of the earth's mantle that underlies its tectonic plates, to rise and lift the overlying crust. Another possibility is that the uplift was the result of heating at the base of the crust. This transformed the lowest crustal rock from eclogite, a relatively dense rock (3.6 g/cm3) to garnet granulite, which is significantly less dense (2.9 g/cm3). This would have produced the buoyant forces needed to uplift the region.
Whatever the cause of the uplift, it resulted in the erosion of up to a mile of overlying sediments from the eastern Grand Canyon. This exposed the Navajo Sandstone, the surface rock found throughout the Horseshoe Bend area which also forms the entire depth of the canyon walls of the Grand Canyon at Horseshoe Bend. This sandstone is notable for its crossbedding and iron concretions.
Horseshoe Bend
An alternate fisheye lens view of the Colorado River in the Horseshoe Bend, Page, Arizona
Horseshoe Bend is a superb example of an entrenched meander. Six million years ago, the region around Horseshoe Bend was much closer to sea level, and the Colorado River was a meandering river with a nearly level floodplain. Between six and five million years ago, the region began to be uplifted. This trapped the Colorado River in its bed, and the river rapidly cut downwards to produce Horseshoe Bend as we see it today.
The cause of this uplift is still a matter of research. One hypothesis is that uplift was a result of delamination, where the lowest layer of the North American tectonic plate below the Colorado Plateau detached and sank into the underlying mantle. This would have allowed hotter rock from the asthenosphere, the part of the earth's mantle that underlies its tectonic plates, to rise and lift the overlying crust. Another possibility is that the uplift was the result of heating at the base of the crust. This transformed the lowest crustal rock from eclogite, a relatively dense rock (3.6 g/cm3) to garnet granulite, which is significantly less dense (2.9 g/cm3). This would have produced the buoyant forces needed to uplift the region.
Whatever the cause of the uplift, it resulted in the erosion of up to a mile of overlying sediments from the eastern Grand Canyon. This exposed the Navajo Sandstone, the surface rock found throughout the Horseshoe Bend area which also forms the entire depth of the canyon walls of the Grand Canyon at Horseshoe Bend. This sandstone is notable for its crossbedding and iron concretions.