Sunday, October 13, 2013

The Multi-Colored Crater Lakes Of Kelimutu

Mount Kelimutu, with its multi-colored crater lakes, is the amazing natural phenomenon in central Flores Island of Indonesia. Kelimutu is a passively degassing stratovolcano capped by three crater lakes containing exotic fluids and whose physico-chemical expressions have changed dramatically through the years. Three crater lakes are located on the eastern summit of Kelimutu. Each of the lakes has a distinctive physical structure, a unique geochemical and hydrothermal regime, and a particular historical sequence of color changes controlled by changes in physico-chemical conditions. The visitor is never quite sure what color the lakes will be when they reach the top as they vary significantly. Unlike other crater lakes where the color variation can be predicted, this is not the case with these three lakes. The colors that you can see here are blue, green and black (and they predominate) yet the lakes also change to white, red and blue too.

The first lake is named Tiwu Ata Mbupu (lake of the ancestors’ souls ); the second is named Tiwu Nuwa Muri Koo Fai (lake of young people’s souls); and the third is called Tiwu Ata Polo (lake of evil spirits).

Tiwu Ata Mbupu, is the western-most lake and is structurally different from the other two in that the pit crater it is in is itself located in the center of a larger crater. Small landslides constantly add to the steep rubble slopes along the lake’s shore, and large boulders periodically drop into the lake. TAM’s shoreline is coated with a film colored in different shades of red, orange, and yellow depending on how thick it is. Gypsum crystals grow in the cracks of the crater wall in the first few meters above the prosent water surface.

Tiwu Nua Muri Koo Fai, is adjacent to Tiwu Ata Polo and is the deepest lake. A sizable tear in the western wall was the location of a pre-1929 breaching and overflow event. Subaerial fumarolic or hydrothermal activity is implied by a large thermal plume in the center of the lake which slowly convects the water. A fresh supply of yellow froth is brought up by the plume and pushed out toward the crater wall. A particularly large cover of this froth has accumulated at the base of the north wall. During rainstorms the froth is scattered by inflowing water and landslides, though some of it may be disappearing altogether.

Tiwu Ata Polo, lies on the southeastern side of the volcanic peak. A thermal plume in the northwest part of the lake indicates underlying subaerial fumarolic or hydrothermal activity. A white froth is present on the lake’s surface around the plume when the convective activity momentarily increases. Rock debris is often carried into Tiwu Ata Polo during rainstorms by water draining the volcano summit around the lake. Two peaks abutting the crater rim help stabilize the east and northeast crater wall, while further around to the southeast a dip suggests a possible one-time overflow outlet. Such an outlet would have fed the river Ria Mbuli, whose upland source is in that area.

Tiwu Ata Polo and Tiwu Nua Muri Koo Fai are only separated by a steep parabolic partition that arcs down to a minimum height of ~35m above the surface level of the lakes. Many Indonesian guidebooks describe the vibrant colors of the Kelimutu lakes as resulting from the minerals in the lakes. While this is partly correct, the most important determinant of color in the lakes is oxygen. Just like your blood, when the lake waters lack oxygen they look green. Conversely, when they are rich in oxygen, they are a deep red to black.

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