Researchers have traced tremor signals deep inside Tanzania's Oldoinyo Lengai volcano, locating them in three dimensions for the first time. The study reveals linked tremors at varying depths, providing insights into magma and gas movement. This unique carbonatite volcano's fluid, cool magma produced unexpected results that could improve eruption forecasting.
Professor Dr. Miriam Christina Reiss, a volcano seismologist at Johannes Gutenberg University Mainz, and her team monitored Oldoinyo Lengai for 18 months using seismometers around the volcano. They analyzed a nine-week segment of data, identifying diverse tremor signals originating from different depths.
"We were not only able to detect tremor, but also to determine its exact position in three dimensions—its location and depth below the surface," said Reiss. "What was particularly striking was the diversity of different tremor signals we detected."
The tremors include one type at around five kilometers depth and another near the volcano's base, occurring with a time delay and appearing linked. Tremors arise when magma ascends, cracking rock or pushing through conduits, or when gas bubbles escape under pressure.
Oldoinyo Lengai stands out as the world's only active carbonatite volcano, with lava that is unusually fluid and cool at about 550 degrees Celsius, compared to the 650 to 1,200 degrees typical of most magmas. "The results were particularly surprising because the magma is so fluid. We had expected few or no tremor as the interaction with the surrounding rock would likely be weaker," noted Reiss.
These findings, published in Communications Earth & Environment, offer clues to volcanic internal dynamics. "Tremor occurs whenever magma is moving—including before eruptions," Reiss explained. "But which tremor signals are true precursors of an eruption, and which are just background 'gurgling'? Our results lay the foundation for improving eruption forecasting in the future."