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Caldera chronicles: A volcano safari to Africa
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CALDERA CHRONICLES

Caldera chronicles: A volcano safari to Africa

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Caldera from space

Ngorongoro volcano, in Tanzania, east Africa, is a caldera that formed 2-3 million years ago. The Ngorongoro Conservation Area is a UNESCO World Heritage Site and home to one of the densest concentrations of wildlife in Africa. 

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week’s contribution is from Dan Dzurisin, emeritus geologist with the U.S. Geological Survey.

Africa is best known for BIG things, including Earth’s largest desert (the Sahara), longest river (the Nile), and largest land mammal (the African elephant). Mount Kilimanjaro volcano in Tanzania, celebrated in Ernest Hemingway’s "The Snows of Kilimanjaro" and later in The Lion King series, is also Africa BIG. It’s the highest mountain on the continent and the highest single free-standing mountain in the world at 5,895 meters (19,341 feet) above sea level and about 4,900 meters (16,100 feet) above its base. But a closer look reveals that the superlatives don’t end there.

Less well known is the fact that Africa is home to more than 100 volcanoes that have been active during Holocene time (roughly the past 10,000 years), including one of the most voluminous and dangerous lava lakes on Earth, and to a rift system that’s actively splitting the continent apart. And there are deforming calderas that have similarities to Yellowstone, too.

Nyiragongo volcano, in the Democratic Republic of the Congo, is one of the most active volcanoes in the world, having erupted at least 34 times since 1882. In 2002 and 2021, the large lava lake at its summit drained and fed lava flows that raced down the volcano’s flanks toward and into the crowded city of Goma, forcing hundreds of thousands of people to flee and resulting in significant damage and even some deaths. Nyiragongo’s lavas are unusually fluid owing to their high temperature (1100 degrees Celsius, or 2000 degrees Fahrenheit) and low silica content (36%, compared to 46%–50% for most basaltic lavas and over 74% for Yellowstone’s rhyolites). Their extreme fluidity has been compared to that of water (an exaggeration), but the risk they pose to vulnerable people and infrastructure is acute.

Erta Ale volcano, in Ethiopia, lays claim to one of the longest-existing lava lakes, having been active continuously since at least 1967, and possibly since 1906. At times, the volcano has hosted not one, but two roiling lava lakes in its summit caldera.

The prevalence of volcanism in Africa is due in large part to the East African Rift, where crustal spreading driven by plate tectonics is splitting the continent apart. Spreading has progressed to the point that new ocean crust has formed in two areas, creating the Red Sea and the Gulf of Aden. On the remaining part of the African continent, rifting has produced the East African Rift valley, which extends from Ethiopia and Eritrea in the north for thousands of kilometers into the heart of Africa — a setting conducive to plenty of active volcanism.

Africa is also home to several notable calderas, including picturesque Ngorongoro Crater in Tanzania, a UNESCO World Heritage Site and a world-class wildlife safari attraction. Ngorongoro has been described as the largest unflooded, intact volcanic caldera in the world. The crater is about 20 kilometers (12 miles) across, 600 meters (1,970 feet) deep, and covers 300 square kilometers (110 square miles). Within its rim there are an estimated 30,000 animals, including lions, leopards, cheetahs, and elephants, making this one of the densest concentrations of wildlife in Africa.

InSAR — a technique that uses satellite images to measure ground deformation — has identified four actively deforming volcanoes along the vigorously active Ethiopian segment of the East African Rift. At Aluto caldera, two pulses of rapid inflation (10–15 centimeters, 4–6 inches) in 2004 and 2008 were separated by gradual subsidence, reminiscent of Yellowstone’s “heavy breathing” during historical time. Deformation also was observed at Haledebi volcano (uplift, August–November 2007), in the area between Bora Berrichio and Tulla Moje volcanoes (uplift, 2008–2010), and at Corbetti caldera (subsidence, 1997–2000). Modelling indicates the deformation sources are likely shallow (less than 10 kilometers, or 6 miles, deep), frequently replenished zones of magma storage and/or associated hydrothermal systems, again reminiscent of Yellowstone.

Aluto is also notable for another reason. At least four large-volume (greater than 10 km3, or 2.4 mi3) caldera-forming eruptions occurred during a pulse of volcanism in Ethiopia between 320,000 and 170,000 years ago, at the dawn of modern humans. Researchers speculate that eruptions from Aluto were large enough to have influenced the dispersal of hominin populations in East Africa. Apparently, the complex relationship between humans and volcanoes that we experience today has its roots deep in pre-history.

These are just a few of Africa’s fascinating volcanoes. So, the next time you ponder the vastness of the Sahara or the mysteries of the Nile, lend a thought also to the snowfields of Kilimanjaro and the continent’s many other volcanic marvels.

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