Band-e Amir Lakes

The Band-e Amir Lakes lie among the foothills of the Hindu Kush, the second highest mountain range in the world.

Of the six lakes, Band-e Panir is the smallest, with a diameter of approximately 100m (330ft). The largest is Band-e Zulfiqar, which measures some 6.5km (4mi) in length.

The deep blue color of the lakes is due to the clarity of the air as well as the purity of the water.

The Band-e Amir River draws its water from the spring melt-water in the surrounding mountains. This gentle outflow of water seeps into the ground and percolates slowly through the underlying limestone, dissolving its principal mineral, calcium carbonate.

Dripping water collects to form underground pools and streams in the caves and passages left behind by the dissolved rock. As they emerge from the hills, the streams become the headwaters of the river.

Laden with dissolved calcium carbonate and other minerals, the river tumbles into a narrow, twisting valley, no more than 12km (7mi) in length.

Each lake is dammed by a long ridge of rock and lies at a different level to its neighbors, thus allowing the river to flow from one to the next.

Dams of Travertine

Aquatic plants grow in the patches of swamp that are created by the streams slowly meandering between the lakes. These plants release a chemical that reacts with the calcium carbonate dissolved in the water and forces it out of solution.

Under the intense heat of the sun, the mineral hardens into a pale waxy substance known as travertine.

Over many centuries, travertine deposited around the margins of the lakes, have created dams that trap water in increasingly large basins. These dams are usually about 10m (33ft) high and 3m (10ft) thick.

As water from the highest lake becomes filled with river water, the water trickles over the lake's travertine dam and then flows toward the next highest lake, and the deposition process continues.

The Hindu Kush

The Hindu Kush extends 800km (500mi) from northeast Afghanistan to northern Pakistan where its tallest peak, Tirich Mir, is 7,692m (25,236ft) in height. Only the Himalayas are taller.

The peaks around the Band-e Amir Lakes rise to around 3,000m (10,000ft) in height.