The biggest volcano in the world is Mauna Loa, a volcano on the big island of Hawaii. Mauna Loa is next to the biggest mountain in the world, Mauna Kea and both of these mountains along with other land masses form the actual island. This volcano is about 1,000,000 years old and is one of the most active volcanoes on the earth and from base to summit is almost 11,000 meters; the base being 13 kilometers under the ocean. In fact, the Hawaiian Islands were formed by volcanic activity.
Mauna Loa is a Shield volcano with gently sloping sides forming a large, gently sloping rocky mound. The lava oozes gently; comparatively, out of fissures in the earth. This is different from a Stratovolcano, like Mt. St. Helens that erupts in a spectacular explosion of lava and ash that travels high into the air. Mauna Loa last erupted in 1984.
Mauna Loa, and the Hawaiian Islands are on the Pacific tectonic plate, one of the 7 major plates on earth. Gradually, over time, the Pacific Plate will move away from the hotspot upon which it sits, and a new island chain will likely form when new rock is generated; in geologic time; hundreds of thousands of years, so no need to liquidate real estate in Hawaii just yet. Movement of these plates is responsible for volcanoes, earthquakes and tsunamis along with the formation of islands including Iceland. Plate tectonics are also responsible for massive mountain ranges like the Himalayan and Rocky Mountains. Plate tectonics caused the breakup of the massive land mass known as Pangaea. Ever notice how the continents look like they fit together like puzzle pieces? Well, they were once all part of a giant, continuous land mass. Plates floating on magma gradually began to separate into the continents that we know today. The Himalayan Mountains were formed when India, formerly an island, smashed up against Asia. Similarly, the Rocky Mountains were formed when a large floating landmass crushed against North America. I like the study of Plate Tectonics; very cool stuff.