This EarthCache examines the formation of river
meanders and oxbow lakes, common features of flat land
rivers.
The Stanislaus River flows slowly into the flat Central
Valley. In such areas of low slope, a typical river's path wanders
back and forth creating meanders, or curves. Along each curve, the
river's current continuously erodes the outside bank of the
meander, while at the same time depositing material on the inside.
This is because the area of fastest flow in the river is forced to
the outside bank on the curves and the slowest flow is on the
inside. Faster water carries more sediment causing the erosion. The
slower water is unable to carry as much sediment. So some sediment
drops out of the water. The result is a steep bank on the outer
edge of a meander and a gentle slope on the inner edge.
Over time, meanders get larger and more pronounced as the
current washes away the outer edge while depositing material along
the inner edge. Given enough time, the meanders could get so curvy
that they bend back the river and make it touch itself to create an
oxbow lake.
An animation of river meander formation can be found at http://www.cleo.net.uk/resources/displayframe.php?src=309/consultants_resources%2F_files%2Fmeander4.swf
In areas that flood regularly, oxbow lakes quickly fill in with
sediment.
The listed coordinates take you to one end of an oxbow lake. You
will have to wander a few yards in various directions to understand
the earth science here. But don't trample the tussock grass, which
the rangers are trying to restore. They also don't want people
wandering onto 'the island' that the lake mostly surrounds.
Logging requirements
Send me a note with :
- The text "GC2JMCZ Oxbow Lakes of the Lower Stanislaus River" on
the first line
- The number of people in your group.
- At this location while looking at the river, where is the area
of most erosion and why do you think it is located there?
- Roughly what percentage of the river's width are you from the
highest velocity water flow?
- What material are you standing on and why is it located
here?
- How close to creating an oxbow lake is this meander? (To really
know the answer to this, you will likely have to follow the
official trails to the alternate viewing point.)
brochure and trail map of the state park
Feel free in your email or your log to speculate about how many
oxbow lakes are in the area and how many will form.
The above information was compiled from the
following sources:
- All images from Prof. Stephen A. Nelson, Tulane
University.
http://www.yosemite.ca.us/library/geology_of_yosemite_valley/
Trial listing approved by