Friday, June 20, 2014

A Rock Outcrop, a River, and Sand flow into a Point Bar...

And the bartender said "is this some kind of joke?"
But it's not a joke of course, it's a simply stunning example of what happens when water flows over stone for a long time. What you are seeing here Horseshoe Bend on the Colorado River a few miles downstream of Glen Canyon Dam and Lake Powell outside of Page, Arizona.

A point bar is a real thing with rivers. When a river loops back and forth as a series of meanders, point bars form as sand ridges develop on the inside of the loop where the water flows more slowly. In the most technical sense, the sand bars in the picture above can be consider an example of the feature, although they are more familiar where rivers are flowing in flat floodplain.

It's obvious that Horseshoe Bend is no longer a flat floodplain! It may have been one at one time, but uplift of the Colorado Plateau (or the subsidence of the lands around the edge of the plateau) caused the river to speed up and start to erode downwards, forming an entrenched meander.
The approach to Horseshoe Bend is a sandy trail about three-quarters of a mile up from a parking lot about five miles south of Page on Highway 89. Although views are wide-ranging along the trail, there is barely a hint of the incredible view that awaits when one arrives at the brink of the cliff and looks down nearly a thousand feet to the river. Stunning is the only word for it.

My old camera couldn't show the entirety of Horseshoe Bend, so I was thrilled I was able to get these wider angle pictures with my new one. It's almost like looking at a petrified rainbow, although it should be said, this view is not entirely natural.

When Glen Canyon Dam was completed in the 1960s, the river was changed forever in terms of a human lifetime. Instead of the normal red silt-laden water, the river flows clear and cold (almost refrigerator cold, about 46 degrees; I can attest to this as I almost drowned in the river last year). As a result, green algae grows in the unnaturally blue river. It's beautiful to look at, but is kind of sad to consider what it should have been. Many of the native species of river life are in decline and cold-loving invasive species are thriving.

A trip-planning note just in case you are headed out to the region this summer: Highway 89 between Bitter Springs and Page was closed down by a serious slope failure along the Echo Cliffs Monocline. It may be years, if ever, before the highway will be repaired. In the meantime, the Arizona Department of Transportation has constructed a newly paved highway replacing Navajo Route 20. Although the detour is supposed to be temporary, I suspect it is permanent despite any feelings of the Navajo Nation about a new busy highway in a formerly isolated part of the reservation. There are far fewer engineering problems where the new highway crosses the monocline.
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