Ouki facts for kids

Ouki was an ancient lake that once existed in the Altiplano, a high plateau in Bolivia. Scientists first suggested its existence in 2006. They were studying the history of large lakes in the region.

Before Ouki, another ancient lake called Lake Minchin was identified in 1904. Some scientists now think that some sediments once thought to be from Lake Minchin might actually be from Ouki.

Scientists are still debating if Ouki truly existed. In 2011, some researchers said that the lake might only have existed within the area of what is now Lake Poopó. The formation of Ouki is linked to a major ice age and was likely caused by a lot more rainfall.

What was Lake Ouki like?

Ouki was a very large lake. It reached a water level of about 3,735 meters (12,254 feet) above sea level. You can still see old shorelines from Ouki near Lake Poopó.

The lake might have covered a huge area. This includes the Salar de Uyuni, the Salar de Coipasa, and the Lake Poopó region. However, some scientists think the Uyuni and Coipasa areas might have been filled by a different lake called Salinas.

The size of Ouki depended on how high its water level was. It could have been anywhere from 10,400 to 46,500 square kilometers (4,000 to 17,950 square miles). That's a massive amount of water!

Ouki was one of several "deep lake cycles" in the region. Another famous one is Lake Tauca. Ouki and Tauca were separated by a time when water levels dropped very low.

The lake left behind special rock formations called tufa. These tufa deposits often look like upside-down cones. The deepest part of Ouki was probably around 80 meters (260 feet).

Some scientists believe that the later Salinas lake might just be a smaller version of Ouki. Also, some of the evidence for the older Lake Minchin might actually be from Ouki. In the future, scientists might even divide the Ouki lake period into smaller stages.

Animals that lived in Ouki

Life thrived in Lake Ouki! It was home to different types of creatures. These included tiny Pisidium clams, small crustaceans called ostracods, and a snail known as Biomphalaria andecola.

The water in Ouki had a high amount of a chemical element called strontium. Scientists have used strontium to try and figure out where the lake's water came from. Some think most of the water came from the Poopó basin. Others believe a large part (about 69%) came from Lake Titicaca. Water from the Poopó basin would have flowed into the Uyuni and Coipasa areas.

When the lake dried up, it left behind deposits of various minerals. These included amphibole, illite, plagioclase feldspar, potassium feldspar, kaolinite, pyroxene, quartz, and smectite.

How old is Ouki?

Scientists have tried to figure out Ouki's age using different methods. They have dated samples of tufa, wood, and fossils from snails found in the Lake Poopó area.

There's a bit of a puzzle with the dates. Two main dating methods give different results:

• Uranium-thorium dating suggests Ouki existed between 120,000 and 98,000 years ago.
• Radiocarbon dating gives younger ages, between 45,200 and 28,200 years ago.

Radiocarbon dating can sometimes be tricky with very old samples. They can get contaminated by newer carbon, which makes them seem younger than they really are. The uranium-thorium dates are generally considered more reliable for Ouki, placing it between 96,740 and 125,990 years ago.

Scientists believe that between 115,000 and 100,000 years ago, Ouki's water level was higher than 3,720 meters (12,200 feet). Some of the changes in Ouki's water levels match cold periods in the North Atlantic. This suggests Ouki existed during a time known as marine isotope stage 5.

Why did Ouki form?

Ouki likely formed because there was a big increase in rainfall. This increase might have been as much as 50-100% more rain than usual. This extra rain could be linked to changes in global weather patterns, like the position of the ITCZ and conditions similar to La Niña.

The time when Ouki existed was also a period of major glaciation, or an ice age. Evidence of this ice age can be seen in moraine deposits (piles of rocks left by glaciers) in the southern Altiplano.

During Ouki's time, the southern hemisphere had less direct sunlight in summer. However, the South American monsoon (a seasonal wind bringing heavy rain) expanded southward. This combination of factors likely contributed to the lake's formation.

Other places also show signs of humid conditions during the Ouki period. For example, lake levels were low in Lake Huinaymarca (part of Lake Tauca). But in the Majes River valley and the Atacama Desert, there's evidence of very wet conditions. This wet period in Peru might even be linked to some very large landslides that happened there.