Olympus Mons on Mars is the tallest volcano in the solar system, rising nearly three times higher than Mount Everest and sprawling wider than France. Its colossal size and mysterious volcanic history continue to captivate scientists.
A Giant Among Giants: Olympus Mons on Mars
Olympus Mons stands as a testament to the raw power of Martian geology. Towering over the red planet’s surface at a staggering 16 miles (25 kilometers) high and stretching 374 miles (601 kilometers) wide, it makes even the largest volcanoes on Earth look small by comparison. In sheer volume, it holds nearly 100 times more lava than Earth’s Mauna Loa, the tallest volcano on our planet. For perspective, Mount Everest, Earth’s tallest mountain above sea level, stands 5.5 miles (8.8 kilometers) tall—just a third the height of Olympus Mons. The Martian volcano’s width equals that of the entire country of France, and Arizona could comfortably nest within its base.
The Martian Landscape and the Concept of “Sea Level”
Unlike Earth, Mars lacks oceans and traditional sea level benchmarks. Instead, scientists use a reference sphere called the “areoid”—a theoretical average of the Martian equatorial radius—to measure elevation. Against this imaginary baseline, Olympus Mons rises around 13 miles (21 kilometers), still setting the record as the tallest planetary mountain known. Yet due to its vast size and gentle slopes averaging only a 5% incline, standing on Olympus Mons wouldn’t feel like standing on a mountain. You’d likely perceive it as a slow upward climb across a massive plain, not a steep peak.
How Olympus Mons Formed: The Power of Shield Volcanoes
Olympus Mons is classified as a shield volcano—a type formed by slow, steady lava flows rather than explosive eruptions. This formation style gives it its signature broad, squat shape. Unlike the rugged profiles of volcanic peaks like Mount Fuji, Olympus Mons rises smoothly and steadily over vast distances. The volcano features six overlapping calderas—collapsed craters at its summit—spanning 53 miles (85 kilometers) across. These formed as underground magma chambers emptied and the unsupported ground above gave way. The edge of Olympus Mons is lined with a dramatic escarpment that rises as high as 6 miles (10 kilometers) in places, creating towering cliffs above the surrounding plains.
Still Active? Recent Activity and Surface Clues
The relatively unscarred surface of Olympus Mons, with few impact craters, suggests its uppermost lava flows are geologically young—possibly as recent as 25 million years ago. That’s a blink of an eye in geological terms and raises the possibility that the volcano could still be active today. Some scientists believe Olympus Mons might even host rock glaciers—masses of rocky debris embedded in frozen water. These glaciers, potentially insulated by dust and ice, may be just 4 million years old, and their features include ridges, furrows, and lobes covered in rocks and boulders.
Why Mars Hosts the Solar System’s Largest Volcano
So why did such a colossal volcano form on Mars and not on Earth?
A key reason lies in the differences in planetary geology. Mars has weaker surface gravity and lacks active plate tectonics. On Earth, tectonic plates move over hot spots in the mantle, forming island chains like Hawaii. Each island is a new volcano that forms as the plate shifts. But on Mars, both the crust and hot spot stay put. This allows lava to pile up in the same location for millions—even billions—of years. This stationary volcanic activity results in single, massive peaks instead of chains. Olympus Mons formed over an immense timespan, and it’s not alone. Three other massive volcanoes in the Tharsis region—Ascraeus Mons, Pavonis Mons, and Arsia Mons—are also enormous. Any one of them alone could claim the title of tallest planetary mountain if Olympus Mons didn’t exist.
Clues from Martian Meteorites
Understanding the formation and age of Olympus Mons comes partly from Martian meteorites that have landed on Earth. A group of volcanic rocks called nakhlites reveals that eruptions occurred over a period of at least 90 million years. That’s an incredibly long lifespan compared to Earth’s volcanoes, which tend to be active for only a few million years. Some meteorites are even older. NWA 7635, a Martian meteorite found in the Sahara Desert, is believed to be 2.4 billion years old—suggesting that the same magma plume may have existed beneath the Tharsis region for over two billion years. Such long-lasting volcanic activity is unheard of on Earth.
From Ancient Observations to Modern Mapping
The sheer size of Olympus Mons means it can even rise above Mars’ infamous planet-wide dust storms. Italian astronomer Giovanni Schiaparelli was able to observe its silhouette with an 8-inch telescope in the late 1800s. When NASA’s Mariner 9 spacecraft orbited Mars in 1971, it captured images of the volcanoes protruding above thick clouds of dust. Today, modern spacecraft like the European Mars Express have used high-resolution stereo cameras to create detailed mosaics and 3D terrain models of Olympus Mons, providing breathtaking views from orbit.
Future Exploration: Real and Virtual Adventures
Although sending rovers or crewed missions to Olympus Mons is challenging due to the thin atmosphere and loose, dusty terrain, plans are already being imagined. A group of Swedish students proposed a mission to scale the volcano by 2042, with rovers ferrying explorers close to the summit before they hike the final stretch on foot. For now, a virtual experience might be the closest most people can get. A company called 4th Planet Logistics aims to create a VR climbing simulation, allowing users to “scale” Olympus Mons from home.
