Anchored Dunes

For thousands of years, the people on the coast of what is now northern Peru lived by harvesting the bounty of the Pacific Ocean. They gathered shellfish, and left big piles of shells and other debris on the beach. Those piles helped anchor long, sandy ridges on the beach against the wind and waves, so some of the ridges are still in place today. The ridges formed as a result of earthquakes, El Niño events, and the normal ebb and flow of the oceans. Earthquakes loosened rocks and soil in the mountains that were then washed downstream by rivers. Rainfall from strong El Niños also brought down fresh material. Tides and storms then sculpted the raw material into ridges that can stretch for many miles.

Researchers discovered that some of those ridges have sharp crests. When they dug into those ridges, they found the remains of human activity, including piles of shells, rocks that had been cracked by fire, and other artifacts. Those remains trapped the sand and pebbles in the ridges, and kept them from being blown away by the winds or washed away by storms.

But the piles of debris stopped being built about 500 years ago — when Spanish conquistadores defeated the Inca empire. The conquest decimated the native populations, leaving the coastline with few settlers — and no new piles of shells and rocks. So over the past five centuries, the ridges on Peru’s northern coastline have come and gone with the wind and waves, unhindered by the hand — and the debris — of human settlers.