Mars is a planet of extreme topographical contrasts, boasting both the deepest canyons and the largest mountains known in the solar system. A precise count of mountains is impossible because Mars hosts a multitude of elevated structures, ranging from massive volcanoes to smaller, non-volcanic peaks. These features were shaped by ancient geological forces, including volcanism, impacts, and wind erosion.
Defining a Martian Mountain
Planetary scientists cannot provide a simple number for the total mountains because the term “mountain” lacks a standardized, universal definition. On Earth, elevation is measured above sea level, but on Mars, scientists must use a hypothetical planetary datum defined by a specific atmospheric pressure level. This reference point can shift depending on the feature’s location and surrounding topography.
Scientists often rely on local relief—the height difference from the base to the peak—to classify an elevated feature as a mountain. This measurement is complicated by enormous geological features like the Tharsis Rise, a crustal bulge nearly 10 kilometers high that serves as the base for several volcanoes. Distinguishing between a true mountain and an uplifted mesa or large hill remains an inexact process, especially given the sheer size of many Martian peaks.
The Tharsis Bulge and Shield Volcanoes
The most massive mountains on Mars are the shield volcanoes concentrated in the Tharsis region, an enormous volcanic plateau near the equator. These structures are the largest mountains discovered in the solar system, dwarfing Earth’s tallest peaks. Their immense size results from Mars’s lack of plate tectonics, which allowed magma to erupt from the same fixed location for billions of years.
The most recognized is Olympus Mons, an extinct shield volcano that stands approximately 22 kilometers high, nearly three times the height of Earth’s Mount Everest. Olympus Mons is about 600 kilometers in diameter, and its base is surrounded by an escarpment up to 8 kilometers high. Its structure developed from the slow, steady accumulation of fluid basaltic lava flows.
The Tharsis region also hosts three other colossal volcanoes, collectively known as the Tharsis Montes: Arsia Mons, Pavonis Mons, and Ascraeus Mons. Each measures between 350 and 400 kilometers in diameter and stands roughly 17 kilometers above the surrounding plains. Their formation along a linear trend suggests a large, underlying fracture zone fed their long-lived volcanic activity. The immense weight of these four volcanoes and the Tharsis bulge has caused the planet’s crust to deform over a vast area.
Non-Volcanic Mountain Structures
While the Tharsis volcanoes dominate the Martian skyline, many other mountain structures were formed by different geological processes. One common type is the central peak found within large impact craters, formed by the rebound of the crater floor immediately after the impact event. These central peaks can rise several kilometers high, resulting from the temporary liquid-like behavior of solid rock following the shock.
Another class of non-volcanic mountain is the layered mountain, an erosional remnant of immense sedimentary deposits. The most notable example is Aeolis Mons, informally known as Mount Sharp, located in the center of Gale Crater. This mountain rises about 5.5 kilometers and is composed of distinct rock layers, suggesting a long history of deposition from water and wind.
Scientists believe the material that formed Aeolis Mons may have once completely filled Gale Crater. The mountain is what remains after eons of wind erosion carved away the softer surrounding rock. These layered structures provide a vertical record of Mars’s ancient environmental history, with each layer representing a different period of sedimentation.