The biggest mountain in the world is actually a volcano; Mauna Kea is 10,206 meters from base to summit; keeping in mind that the base is several thousand meters below sea level and we only see the top 4,000 meters. Mauna Kea is one of 5 volcanoes that make up Hawai’i. Its neighbor, Mauna Loa is the second biggest mountain in the world at 10,099 meters from base to summit. The exact figures vary depending upon which source you look at for the heights of these two giants, but the fact remains; there is only just over 100 meters separating the two peaks, and BOTH are taller than Mount Everest. To further complicate matters, Mauna Loa is much larger in mass than Mauna Kea, so depending upon how you define “biggest”, either answer is correct.
Mauna Loa and Mauna Kea are known as Shield volcanoes. Lava, from a fissure deep in the ocean bubbles out and cools to form a gently sloping, rocky mound. Over time, more and more lava flows out and hardens and the rocky mound gets higher. This type of volcano is completely different from a stratovolcano, like Mt. St. Helens in Washington State. Shield volcanoes are shorter and wider in shape and erupt in a slower, milder oozing of lava, whereas stratovolcanoes are tall and slender and tend to explode into spectacular plumes of jetting lava and ash.
Mt. Everest is the largest land based mountain that stands 8,848 meters. To get nitpicky (and I like to sometimes), Mt. McKinley in Alaska has a higher rise than Mt. Everest. Basically what this means is if you were standing at the base of Mt. Everest, you would already be 5200 meters above sea level. To get to the top, you would need to climb 3700 meters. If you were standing at the base of Mt. McKinley, you would only be 610 meters above sea level. To get to the top, you would need to climb 5500 meters.