The Only Natural Lake In Ghana Has Extraterrestrial Origins

Lake Bosumtwi in Ghana is no ordinary lake. If it looks a little bit out of place in the surrounding landscape, that’s because it is. It is the only natural lake in the country, formed just over 1 million years ago when a meteorite from outer space crashed into the rainforest, leaving behind a crater that was eventually filled with water.

Spanning around 10.5 kilometers (6.5 miles) in diameter, the Lake Bosomtwe impact crater is located in the mineral-rich Ashanti gold belt of Ghana. 

The site is now recognized as one of the best-preserved impact craters in the world and the most recent of its size. It is also one of just 190 confirmed impact craters on Earth, only some of which contain lakes, making this an extremely special site.

Scientists started to wonder whether the lake was a meteor crater in the 1930s, although some speculated it may be a caldera formed by a volcanic eruption or the result of tectonic movement. By the 1960s, studies confirmed that the area had been struck by a high-energy object around 1.07 million years ago, based on geological evidence of shock metamorphism and the presence of minerals that form only under extreme temperatures.

Clearly, the space rock that forged this crater was huge. Later geochemical analysis has suggested the meteorite was rich in iron and had a mass of approximately 100,000,000 tons.

The exact origin of the meteorite is unknown. We don't know where it came from, nor the literal impact it had on life on Earth. However, a meteorite of this size and strength must have caused quite a cataclysm.

An impact of such magnitude could have unleashed tremendous amounts of energy, powerful enough to launch vast clouds of dust into the atmosphere, dim the Sun, and temporarily cool global temperatures. Strangely, unlike other major impact events etched into the planet’s geological memory, no such global markers have yet been linked to Lake Bosumtwi.

For some people, the significance of Lake Bosumtwi goes beyond geology. Sacred to some members of the local villages, its abundant waters are viewed as a symbol of divine favor and God's generosity. The lake’s name comes from obosom (meaning “God”) and ɔtwe (meaning “antelope”).  

Along with holding a deep spiritual significance, the lake is integral to day-to-day life here. A survey of 170 people who live around the lake found that most residents use its waters for cooking, cleaning, bathing, and recreation. 

Unfortunately, the local landscape is under threat. Writing for The Conversation, Marian Selorm Sapah, a geochemist and senior lecturer at the University of Ghana, explains that “immediate action is required” to manage the onslaught of illegal mining and deforestation that’s encroaching on and around the crater rim. Left unchecked, she says, the problem could undermine future efforts to scientifically understand the lake and its extraterrestrial origins.