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Photos courtesy of the
Google Earth
Above: This Google Earth shows
the
Milk River as it flows past Zurich, a tiny
town located 30 miles east of Havre. Move your cursor over the image to see the current channel of the Milk River (yellow) and two oxbow lakes (orange). From its headwaters in Glacier Park,
the
Milk River flows northeast into Canada,
before returning to Montana northwest
of Havre. It is a tributary of the
Missouri River, and its confluence with
the Missouri is located southeast of
Glasgow.
Click here to see a larger image which shows more of the Milk River Valley near Zurich. Click here to see several oxbow lakes near Kalispell.
Below: The Milk River is
shown in
yellow. (Move your cursor over the photo to see a normal view.) As with most rivers that flow
through broad flat floodplains, the Milk
River has a tendency to move in
sweeping bends called "meanders".
When a river flows around a curve, the
fastest water is on the outside of the
bend, so erosion is more rapid there.
Over time this "sideways" erosion
causes the
meander of the river to grow wider and
wider. Eventually the curve becomes a
loop that the river breaks through. Such
a shortcut
location marked with the small yellow
X on the photo below. As the river
drops mud and silt at the ends of the
abandoned meander this separates
the
meander from the river, forming an
oxbow lake. They are called "oxbows" because they resemble the oxbows that farmers put over the shoulders of the oxen that pulled plows and wagons. In Australia they are called
"billabongs," and in Louisiana they're
called "bayous". Since it is no longer
part of the river, the waters of the oxbow
are calm, allowing a pond or lake
ecosystem to develop. In time the lake
will disappear as it fills in with organic
material and other sediments. Some of
the other (unlabeled) oxbow lakes on
the photo provide examples of this
filling process. 
Term: floodplain
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