If you found a list of the world's tallest mountains in an atlas or almanac, Mt. Everest, in Nepal, would hear the list. It is more than 29000 feet high. Far down the list would be Mauna Kea, in Hawaii, which rises 13796 feet above the Pacific Ocean. Yet Mauna Kea is really taller than Mt. Everest.
How is that possible? Mauna Kea is a volcano built up from piles of lava. Only about 14000feet of the giant volcano sits above the water. Another 16000 feet ascends from the bottom of the ocean to sea level. So Mauna Kea is really about 30000 feet tall.
How big is Mauna Kea ? If you spread out all of the lava it look to from the volcano, it would covet the entire state of New York with a blanket and ash more than 1000 feet thick!