FLYING south from Istanbul across the Turkish heartland, one can just about make out, beyond the starboard wing, the upper reaches of Buyuk Menderes Nehri. Naturally, one thinks of Milton and The Lady's Song in Comus:
Sweet Echo, sweetest nymph, that liv'st unseen
Within thy airy shell
By slow Meander's mar gent green,
And in the violet embroi dered vale,
Where the lovelorn nightingale
Nightly to thee her sad song mourneth well.
Buyuk Menderes Nehri, you see, was called by the ancient Greeks Maiandros, and is a winding river in that part of modern Turkey that they knew as Phrygia. It flows into the Aegean sea near samos, and pursues such a very winding, sinuous course that its name was adopted as an adjective for any waterway that shows this tendency. A river, it is said, "meanders".
Most rivers have their origins in a mountain spring or lake. The stream, as it runs swiftly down the mountain gullies, follows a course that at first is reasonably straight. As it descends in to the plain, however, and the slope of the ground becomes more gentle and nearer to the horizontal, the river broadens and its speed diminishes; this relatively flat terrain results in a meandering path.
It is interesting to serve why these meanders happen. As a river flows on relatively level ground, it erodes laterally rather, than vertically. Any slight curve in its initial path requires the water to flown more quickly on the outside of the bend than it does on the inside. This results in erosion of the river bank on the outside of the curve, and deposition of material in the relatively slow moving water on the inside. Over time, therefore, each bend becomes more and more pronounced until it can be recognised as a meander. Rather than lashing about wildly in this way over a large area, rivers tend to undulate back and forth within a well defined strip of ground, called the meander belt, defined by the terrain.
Sometimes a meander becomes so exaggerated and pronounced that only a narrow neck of land separates two adjoining portions of the river. In such a situation, when the river flows more quickly in times of flood it may eventually cut right through this neck of land. Deposits later seal off the abandoned meander to create an isolated area of water in the shape of a horseshoe - a so called "ox bow lake".