In Vanuatu, DTM Peers Into ‘Plumbing System’ of Ambrym Volcano
DTM volcanologists Hélène Le Mével and Diana Roman traveled to Vanuatu in May 2019 for a new project that will probe the magma under Ambrym volcano. With measurements of the volcano’s seismicity and gravity, the team will explore the locations of magma reservoirs, how they are connected to each other, and how magma moves in the crust prior, during, and after an eruption. DTM Postdocs Kei Shimizu and Elodie Brothelande also accompanied the volcanologists as field assistants.
“We want to image the magmatic plumbing system underneath,” said Le Mével, a volcano geodesist who is leading the project. “We want to understand how magma moves underground and the processes leading up to an eruption or the intrusion of magma in the crust.”
Similar to the pipes connecting and transporting water under our sinks, Ambrym’s “plumbing system” moves magma from about 30 km (18 miles) underground to the surface. However, unlike our sinks, a volcano’s pipes do not travel straight up in a direct line. Instead magmatic systems comprise many different conduits moving magma through the lower and upper crust and magma reservoirs at different depths.
“The magma also usually stages at different depths for long periods of time, changing the chemistry of rocks,” Le Mével said. “It can stay a few months, or sometimes thousands of years, which makes a very complex crust and plumbing system.”Top left: DTM geophysics postdoc Elodie Brothelande en route to Ambrym volcano. Bottom left: DTM geochemistry postdoc Kei Shimizu, taking samples at Ambrym. Right: DTM Staff Scientist Diana Roman preparing instruments at Ambrym. Photos: Carnegie, DTM.
Le Mével plans to measure gravity at about 200 points at Ambrym over the course of three years with the support of the Brinson Foundation. Her research will help understand the dynamics of magma before it erupts at the surface, how often, and whether the magma is likely to return to the surface to form a lava lake.
In December 2018, Ambrym underwent an eruption that resulted in a lava flow and a fissure eruption near the summit and magma injection into the East Rift Zone, a highly faulted region on the flanks of the volcano. The eruption drained the famed lava lakes at Benbow and Marum craters. A similar eruption occurred last year in Hawaii, when Kilauea’s eruption led to an eruption event that transported lava rivers down into the ocean.
Ambrym is a basaltic shield volcano similar to Kilauea. It’s also one of the most actively degassing volcanoes in the world. But unlike Kilauea, which has been studied extensively for years, Ambrym remains a mostly understudied volcano. “It’s very remote, very hard to get to the top,” Le Mével said. “So it’s hard to do field geophysics in such a system.”
About 1200 miles east of Australia, Ambrym Island is home to over 7000 people. “So we need to take more measurements and understand the system to make better volcano hazard maps and mitigate the risk,” Le Mével said.Hélène Le Mével focuses on using gravity measurements to find patterns between different volcanoes and understand how much magma injection into the crust is needed to trigger an eruption. Photo: Elodie Brothelande, Carnegie DTM.
Roman, a volcano seismologist, is deploying Carnegie Quick Deploy Boxes strategically in order to record the volcano’s magma-generated earthquakes and relate that to Le Mével’s gravity maps. Their work integrates the local observatory’s data.
Le Mével said despite the stunning landscapes of the volcano and excellent reception by Ambrym locals, the trip was one of the hardest she had done before because of the island’s geography.
“We carry a lot of equipment, and everything is done in hours-long hikes, so that means a lot of backpacking in a hot, tropical, humid jungle,” she said. “But we are getting a lot of good data and are going to learn a lot about the relationship between local tectonic activity and magmatic activity.”
—Roberto Molar Candanosa