How do shield volcanoes get so big?

Shield volcanoes form by inviscid magmas. Inviscid means not viscous or "not resistant to flow." It's basically a scientific way of saying the magma is "runny" like water. Today, shield volcanoes are always basaltic in composition. read more

Shield volcanoes are some of the largest volcanoes in the world. For example, Mauna Kea and Mauna Loa on the big island of Hawaii are examples of shield volcanoes. And so is Olympus Mons on Mars, which towers 27 km above the surrounding plains. read more

These volcanoes require a much larger source of magma at depth so the erupted product is likely to be hotter and maybe a little less differentiated. So, the short answer to your question is this: shield volcanoes are big because they are formed by larger/more active/longer lived magma chambers than smaller basaltic volcanic features. read more

Hawaii is home to a great deal of the planet’s shield volcanoes as the Pacific Plate and the Hawaii hotspot have combined to form a large chain of various volcanoes of all types. This chain includes more than 43 major volcanoes, including Mauna Loa. read more