A shield volcano is so named for its broad dome shape, reminiscent of the convex bulge of ancient Teutonic war shields. Oceanic volcanoes, built up from innumerable highly ﬂuid lava ﬂows, take this form, eventually rising from the seaﬂoor to create islands, including those in the Hawaiian and Galápagos archipelagoes. Mauna Loa, on Hawai‘i Island, is the largest shield volcano, and in fact the largest mountain on Earth. Measured from the ocean ﬂoor, where its footprint is over 180 miles in diameter, it rises over six miles. Its massive dome shape dominates the skyline from the south end of the island, giving the odd impression of a huge moon partly risen over the horizon. Indeed, shield volcanoes are interplanetary features, found on the moon, Mars, and possibly Venus. The moon’s Olympus Mons, over 370 miles in diameter, currently holds the title of largest shield volcano in the solar system.