The mighty Amazon River, a tropical torrent that carries about 20 percent of the fresh water that flows into the world's oceans, starts out as a trickling snow-fed stream.
That's what a five-nation team of explorers funded by the National Geographic Society found when they used the Global Positioning System (GPS) to survey five remote rivers in a 100-square-kilometer area in southern Peru last July.
After setting up a GPS base station and camp at an elevation of about 15,500 feet, small teams braved harsh terrain at even higher altitudes to map the Andean headwaters of the world's largest river. The 22-person expedition found that the source of the Amazon is a small stream that flows from the upper slopes of Nevado Mismi, an 18,363-foot-high peak. National Geographic announced the results of the GPS survey last month.
The source of a river can be defined in several ways, says Andrew Johnston, a geographer at the National Air and Space Museum in Washington, D.C., a