Mauna Loa briefly lost its title of world’s largest volcano in 2013 when, as reported by National Geographic, a team of scientists announced that the designation actually belonged to Tamu Massif, an extinct shield volcano on the seafloor east of Japan that covers 100,000 square miles. Shield volcanoes, as defined by the British Geological Society, are volcanoes with gently sloping sides caused by lava with low viscosity. Mauna Loa is also a shield volcano. In 2019, a team led by William Sager, the lead scientist in the study that proposed Tamu Massif as the world’s largest volcano, reevaluated the original findings and determined that Tamu Massif wasn’t a shield volcano at all, but rather “a colossal collection of 19-mile-thick oceanic crust.” This is still quite amazing, as it’s four times thicker than the global average for ocean crust and the reasons for its existence are still unclear, but it’s no volcano and so Mauna Loa recaptured the title of world’s largest. 

The year 2019 was a significant one for Mauna Loa. In addition to the Tamu Massif discovery, the Hawaiian Volcano Observatory raised Mauna Loa’s alert level from GREEN/NORMAL to YELLOW/ADVISORY. Per Forbes, the alert was updated thanks to some new surface deformation and seismic activity; it had been at this level in early 2018 as well and isn’t cause for panic. The volcano likely wouldn’t erupt without warning, and its level could stay at YELLOW/ADVISORY for years (it’s still there as of this writing).