Final answer:
Olympus Mons is the largest volcano on Mars and in the Solar System. It towers over 20 kilometers above the Martian surface and has a base large enough to cover a state as large as Missouri. Its sheer size is attributed to the lack of plate tectonics on Mars, allowing for continued growth over a stationary hot spot.
Step-by-step explanation:
The name of the largest volcano not only on Mars but also in the entire Solar System is Olympus Mons. This colossal volcano is unprecedented in size when compared to its counterparts on Earth. With a base that would cover the entire state of Missouri, Olympus Mons soars over 20 kilometers above the surrounding Martian plains, which is almost three times the height of Mount Everest, the tallest mountain on Earth. The caldera at the top of Olympus Mons spans about 65 kilometers across, roughly the size of Los Angeles. This Martian volcano's significance is emphasized by the fact that it is nearly 100 times larger in volume than Mauna Loa, the largest active volcano on Earth.
One of the reasons why Olympus Mons is able to reach such staggering heights, in contrast to volcanoes on Earth, is due to the lack of plate tectonics on Mars. Earth's constantly moving crustal plates prevent a volcano from growing too large at any one stationary point. On Mars, however, the crust remains in place over a volcanic hot spot, allowing a volcano like Olympus Mons to expand for millions of years.