Most folks know a river or creek meander when they see one (or more).
Usually we see them in Coastal Plain settings or other places where the stream gradient (feet/mile drop in elevation) is low, especially if the materials underlying the stream are soft Coastal Plain sediments and/or floodplain deposits.
When a stream's gradient is steep, as in a mountain stream, there is a tendency for gravity to control erosion, i.e., the erosion is vertical - down-cutting as we call it. This vertical down-dutting (being slightly redundant) results in sharp "V"-shaped valleys, with no flood plains.
So when you see deeply-incised meanders, such as in the above photo, that suggests that the meanders were established under low-gradient conditions at a higher Base Level (see this post for an explanation of Base Level). Then a rapid drop in Base Level and/or a rapid uplift of the land "preserved" the meanders as the river cut downward through the Colorado Plateau sedimentary rock layers.
Usually we see them in Coastal Plain settings or other places where the stream gradient (feet/mile drop in elevation) is low, especially if the materials underlying the stream are soft Coastal Plain sediments and/or floodplain deposits.
When a stream's gradient is steep, as in a mountain stream, there is a tendency for gravity to control erosion, i.e., the erosion is vertical - down-cutting as we call it. This vertical down-dutting (being slightly redundant) results in sharp "V"-shaped valleys, with no flood plains.
So when you see deeply-incised meanders, such as in the above photo, that suggests that the meanders were established under low-gradient conditions at a higher Base Level (see this post for an explanation of Base Level). Then a rapid drop in Base Level and/or a rapid uplift of the land "preserved" the meanders as the river cut downward through the Colorado Plateau sedimentary rock layers.
The Grand Canyon also illustrates this same rapid uplift/drop in Base Level, as does the area containing the Black Canyon of the Gunnison River, in Colorado, though without the meanders.
No comments:
Post a Comment