The solar system is home to an extraordinary variety of landscapes, ranging from icy plains to towering, fractured surfaces. These celestial bodies often host geological features that dwarf any mountains or valleys found on Earth. The search for the solar system’s ultimate high point reveals the powerful, yet distinct, forces that shape planetary geography across different environments.
The Title Holder: Olympus Mons
The undisputed monarch of the solar system’s mountains is a colossal shield volcano located on Mars. This gigantic feature, named Olympus Mons, resides on the western edge of the Tharsis Rise, a massive volcanic plateau near the Martian equator. The mountain is a sprawling structure built up by thousands of highly fluid, basaltic lava flows over billions of years.
Olympus Mons reaches an astonishing height, measuring approximately 22 to 25 kilometers above the surrounding Martian plain. The base of the volcano spans about 600 to 700 kilometers across, making the entire structure wider than the length of the Hawaiian island chain on Earth. The summit features a complex, multi-ringed caldera, a collapsed crater system that itself is 85 kilometers in diameter.
How Its Size Compares to Earth
The sheer size of the Martian giant becomes clearer when placed next to Earth’s highest points. Mount Everest, the tallest mountain above sea level on our planet, stands at 8.85 kilometers, meaning Olympus Mons is nearly three times its height. The base of the volcano covers an area of roughly 300,000 square kilometers, which is comparable in size to the US state of Arizona.
The volume of material within Olympus Mons is estimated to be about 100 times greater than that of Mauna Loa in Hawaii, the largest volcano on Earth by volume. Because of the volcano’s massive width and gradual, gentle slope—averaging only about five degrees—a person standing on its flank would not feel like they were climbing a mountain. The curvature of the planet would obscure the summit from view if one were standing on the base. Even the steep cliffs that form the outer edge, known as the basal escarpment, are up to eight kilometers high, nearly matching the total height of Everest.
The Martian Geology That Built It
The ability of Olympus Mons to reach such extreme dimensions is a direct result of fundamental geological differences between Mars and Earth. One significant factor is the lower surface gravity of Mars, which is only about 38% of Earth’s. This reduced gravitational pull allows volcanic material to pile up to far greater heights before the weight of the mountain causes the crust to fracture and collapse.
The absence of global plate tectonics on Mars is the second and most important factor for its immense growth. On Earth, tectonic plates move slowly over stationary magma hotspots, resulting in a chain of volcanoes, such as the Hawaiian Islands. Since the Martian crust is stationary, the magma plume beneath the surface fed lava to the exact same location for billions of years. This continuous, focused accumulation of highly fluid basaltic lava allowed the volcano to grow steadily into the colossal shield structure seen today.