The object of interest is the Tamu Massif in the western Pacific Ocean, a New Mexico-sized bump in the oceanic crust that constitutes the world’s largest volcano. This superlative was only bestowed in 2013, when the enormous feature was declared a single structure; the recency of the finding highlights the inherent difficulty of even the most sweeping reconnaissance, when done underwater.
I wonder how it compares to the Yellowstone Caldera. Read the story @ Decoding the World's Largest Volcano - The Extremo Files