Olympus Mons is the largest known volcano and tallest mountain in the solar system, located on the planet Mars. Mount Everest, while holding the title of Earth’s highest peak above sea level, is dwarfed by its Martian counterpart. The vast disparity in their sizes highlights the profound differences in the geological processes and planetary environments of Earth and Mars.
Comparing the Measured Elevations
Mount Everest’s summit reaches an elevation of 8,848.86 meters (approximately 5.5 miles) above Earth’s mean sea level. This height makes it the highest point on our planet accessible from the ocean’s surface. By contrast, Olympus Mons towers approximately 21.9 kilometers (13.6 miles) above the reference level for Mars.
When measured from its base on the surrounding Martian plains to its peak, Olympus Mons stands even taller, with some estimates placing the total vertical relief at up to 25 kilometers (16 miles). This means the Martian giant is roughly two and a half to three times taller than Mount Everest. The enormous shield volcano also spans a base diameter of about 600 kilometers, covering an area roughly the size of the state of Arizona.
Reference Points for Planetary Height
The direct comparison of these two figures is complicated by the different reference systems used to define height on each world. On Earth, elevation is universally measured against Mean Sea Level (MSL), which represents the average height of the ocean surface. This level provides a consistent, albeit dynamic, global datum because the planet is covered by liquid water.
Mars, however, has no liquid oceans, making a true “sea level” impossible to establish. Scientists have therefore created an arbitrary reference surface called the areoid, which is a gravity-based equivalent to Earth’s sea level. Olympus Mons’ official height of 21.9 kilometers is measured above this Martian datum. The height is also often cited relative to the vast, flat plains that surround the mountain’s base, which provides a local, topographic measurement of approximately 25 kilometers.
Geological Factors in Mountain Formation
The tremendous size difference is due to the distinct geological environments of the two planets. Mount Everest is a result of continental collision, specifically the ongoing impact between the Indian and Eurasian tectonic plates. This process of plate tectonics slowly pushes the crust upward, creating steep, jagged peaks like the Himalayas. However, Earth’s active crustal movement also limits the ultimate height of mountains, as tectonic forces are balanced by gravity and constant erosion from wind, water, and ice.
Olympus Mons, classified as a shield volcano, was built up over billions of years by highly fluid lava flows. The lack of plate tectonics on Mars is the most significant factor in its growth. On Earth, a volcanic hotspot eventually moves away from the magma source due to plate movement, creating a chain of smaller volcanoes, like the Hawaiian Islands. Since Mars’ crust is static, the magma plume remained fixed beneath the same spot for eons, allowing lava to accumulate in one massive structure without interruption. The lower gravity on Mars (only about 38% of Earth’s) also allows volcanic structures to grow substantially taller before their own weight causes them to collapse or spread out.