When the Nyiragongo volcano erupted in January 2002, it set the geologic stage for earthquakes nine months later. Julia Rosen reports.
2002 was a tough year for the people who live along the shores of Lake Kivu in the Democratic Republic of the Congo. It started off with a bang, when the Nyiragongo volcano erupted in January. And it tailed off with a shudder, when a magnitude 6.2 earthquake struck the region in October. Both events devastated local communities—and their close timing struck some scientists as suspicious.
“We were wondering if there was a link—so, a causality—between those two major geological events.”
Christelle Wauthier, a geologist at Pennsylvania State University.
From studying radar images of the ground taken before and after the January eruption, Wauthier knew that lava didn’t just spew out of the volcano. It also wedged itself into cracks in the crust, forming what geologists call a dike.
“You can think of it as like a blade-shaped type of magma intrusion, moving from depth toward the surface. It’s very fast, a few hours, a few days, and it can penetrate tens of kilometers of crust.”
Dikes are common in rift zones, like east Africa and Iceland, where tectonic forces are slowly ripping Earth’s crust apart. And they’re known to cause small earthquakes right when they happen. But Wauthier wondered if dikes might also be capable of triggering large earthquakes by pushing the ground apart and affecting nearby faults.
“You will add more stress on a weakness surface, which is a fault. And so if you add enough stress on it, you can trigger failure on the fault.”
Now, Wauthier and her colleagues have used a model to show that the stress changes caused by the January dike event made the October earthquake much more likely to occur. The results are in the journal Geochemistry, Geophysics, Geosystems. [C. Wauthier, et al, Diking‐induced moderate‐magnitude earthquakes on a youthful rift border fault: The 2002 Nyiragongo‐Kalehe sequence, D.R. Congo]
This study marks the first time scientists have linked dike formation to large, damaging earthquakes, and Wauthier is looking back through history for more examples. She says researchers will never be able to predict exactly when an earthquake might strike after a dike intrusion. But at least now, researchers and rift zone residents know they’re not just in for bangs—they may also be in for shudders.
[The above text is a transcript of this podcast.]