Hear about a strange underwater hum that went 'round the world? Neither had we, but scientists say they've found the likely source: a huge underwater volcano off the coast of Africa, LiveScience reports. Rising half a mile from the ocean floor and three miles across, the volcano apparently sprouted up last year. "This thing was built from zero in six months!" geophysicist Marc Chaussidon tells Science. Odd rumblings began disturbing Mayotte, a French island between Mozambique and Madagascar, about a year ago. Then last November, a powerful seismic event near Mayotte nudged the island over a few inches and triggered a seismic hum that circled the globe. Islanders "were getting very stressed, and were losing sleep," a sociologist says.
Scientists got involved by using seismometers that identified a cluster of earthquakes under the earth's crust. Seems the quakes were caused by a deep magma chamber pushing 1.2 cubic miles of molten rock to the ocean floor; that chamber "then contracted, driving the cracking and creaking of surrounding crust," per Science. But questions remain: The volcano likely rose up in 2018, yet Tech Times says its exact age is unknown. What caused the hum is also unclear, but it could be the underwater volcanic eruption. And while the Comoro archipelago—of which Mayotte is part—does have volcanic activity, no eruption had hit the island in over 4,000 years. At least some researchers plan to keep investigating. (Meanwhile, one of the world's newest islands has a mystery.)