A Strandplain on coastal Peru

This image by an Expedition 32 crew member on the International Space Station- ISS, features a strandplain on coastal Peru. Numerous subparallel lines (center) along the arid, difficult to see from the ground, but visible from orbit.   Image credit: NASA

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These lines in northern coast of Peru (about five degrees south of the Equator) are close-packed beach ridges, known collectively as a strandplain (for scale, the strandplain is 30 kilometers long).

Each ridge shows the position of a prior shoreline.

The Chira River delta appears at right, with dark green agricultural fields occupying the delta of the river. A smaller river reaches the sea, without forming a delta, at extreme left.

The prominent cape at lower left is Punta Balcones, a region with many oil wells. Strandplains are built by successive additions of beach sand usually from some nearby source.

Currents on this coast of South America come from the south, suggesting to scientists that the Chira River delta (right) is the source of the sand.

The newest beach is being formed today by the waves—which appear as the thin ragged white line along the strandplain—supplied by the north-flowing current. The regularity of the spacing of the beaches suggests that some episodic influx of sediment controls beach formation. This influx may be determined by floods coming down the Chira River, possibly controlled by the heavy rains of El Nino events which occur irregularly every few years.

via NASA

A Strandplain on coastal Peru, map