Field Report: Ol Doinyo Lengai Volcano, Tanzania

For the first time in 12 years, researchers have collected lava samples from Ol Doinyo Lengai in Tanzania, the only natrocarbonitite volcano in existence. They used homemade gas sensors to study its emissions and rigged up climbing ropes to collect the cool, watery, carbon-rich natrocarbonatite lava bubbling up from its deep crater.

In 2007, Ol Doinyo Lengai volcano in Tanzania erupted explosively, creating a deep crater. Previously, the crater had been filled to overflowing with lava and scientists could walk up and collect a sample with a spoon. A year after the eruption, lava again began to bubble up at the base of the 100-meter-deep crater, but it appeared far out of the reach of scientists.

Rather than waiting for the crater to refill, Reservoirs and Fluxes Community members Kate Laxton (University College London, UK), Emma Liu (University of Cambridge, UK), and colleagues undertook an ingenious and highly successful sampling trip involving rock climbing equipment, cocktail shakers, and hamster balls. They spent eight days and nine nights atop the volcano’s windy summit in late July and early August, working with researchers at the Geological Survey of Tanzania and Dar es Salaam University. By analyzing the composition of the first lava samples collected since the volcano’s eruption, they hope to learn about any recent changes to its underground plumbing system. The researchers also took up-to-date measurements of carbon dioxide emissions to inform more accurate climate models.

“For scientists, Ol Doinyo Lengai is special because it’s the only one of its kind,” said Laxton. The volcano’s natrocarbonatite lava, which she describes as like “molten limestone,” is rich in sodium and carbon and has no silicate minerals, which make up most lavas. As a result, the lava is watery, black, and a “cool” 500 to 600 degrees Celsius. The lava’s composition stayed surprisingly consistent in the 25 years before the eruption. Scientists don’t yet agree on the lava’s source, but many suspect it is a product of a reaction in the crust.

Ol Doinyo Lengai Team 2019
The Ol Doinyo Lengai sampling team included Papkinye Lemolo, Boni Kicha, Ignas Mtui, Boni Mawe, Adadeus Mtui, Emma Liu, Arno Van Zyl, Kate Laxton, and the driver, Baraka. Credit: Baraka 

Lavas from the big eruptions, however, have a silicate composition, providing clues as to the original source of melted rock. “The volcano has a bit of a split personality,” said Laxton. “It likes to have long periods of effusive natrocarbonatite eruptions and then every now and then it will explode violently with a completely different chemistry.” 

Drawing on Laxton’s rock climbing experience, the team set up ropes on a pulley system across the 300-meter-wide crater, with the help of rope technician Arno Van Zyl (Vertica Ltd, UK). Additional Kilimanjaro guides and local Maasai residents rounded out the team. The group was on a budget, so they chose affordable and easily available stainless steel cocktail shakers and cups used to measure wine pours, which they dropped to the bottom of the crater to scoop up the natrocarbonatite lava. “A couple of the big cocktail shakers were claimed by the volcano,” said Laxton.

Kate Laxton
Laxton holds stainless steel wine measures containing the first samples of natrocarbonatite lava taken since the 2007 eruption. Credit: Emma Liu

Using Liu’s gas sensing expertise, the team sent a MultiGAS instrument, borrowed from the University of Palermo, across the crater to collect emissions data from the volcano. They also performed thermal imaging at night and used drones to map out the topography of the crater, which lets them estimate the rates and volume of lava erupting over time.

While the MultiGAS is invaluable for measuring volcanic gases, the researchers were concerned that the high carbon dioxide levels, which have been measured at well over 40% of emissions, would swamp its carbon dioxide sensor. To compensate, they constructed low-budget sensors that could detect up to 100% carbon dioxide and placed them inside hamster balls, which they rolled down the rocky slope to different depths within the crater. The battery-powered “gas eggs,” built with the help of Kieran Wood (University of Bristol, UK), also contained a sensor for pressure, temperature, and humidity, and recorded data from the passing gases onto a memory card. Laxton had considered using a wheeled contraption or even drones, but kept coming back to hamster balls as the best solution. “The idea was to hang them along the rim of the crater, a bit like Christmas baubles,” said Laxton. “It worked beautifully.”

Hamster ball gas sensor
Environmental sensors protected inside a hamster ball provided a budget-friendly way to measure carbon dioxide, temperature, pressure, and humidity at various points within the crater. Credit: Kate Laxton, Emma Liu

By combining trace gas data from the MultiGAS and the carbon dioxide measurements from their homemade sensors, the researchers will be able to calculate the sizable carbon dioxide flux from Ol Doinyo Lengai volcano and its contribution to global volcanic emissions. These measurements can improve climate modeling and help scientists monitor for the next big eruption.

“If we understand more about the day-to-day activity of this volcano and how much carbon it emits, then that can help us track pre-eruptive changes that might give us early warning systems for future eruptions,” said Laxton. 

Ol Doinyo Lengai volcano has erupted violently four times during the past 100 years and is susceptible to overflowing lava, sector collapse, and landslides, which threaten the local people living at its feet. But the volcano is also a sacred place for Maasai across East Africa. In the Maasai language, the volcano’s name means “Mountain of God” and its ash fertilizes the Serengeti plains, nourishing grass for migrating wildebeests and Maasai cattle.      

Laxton said she and her colleagues plan to improve their budget-friendly homemade sensors and share them with their Tanzanian colleagues. The researchers hope that the discreet sensors will help local scientists perform their own volcano monitoring, both for scientific investigations and to warn of future eruptions, without interfering will local religious customs.

Main image: Ol Doinyo Lengai volcano in Tanzania. Credit: Kate Laxton

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