Olympus Mons

How tall is Olympus Mons?

About 22 km (14 mi) at its peak, or 24 to 26 km (15 to 16 mi) measured from the plains around it. ESA puts the peak at 21.9 km (13.6 mi).[1] Mars has no sea level, so maps measure height from a reference surface that plays its part.[6] NASA says the volcano’s summit region stands just over 20 km (12 mi) above that zero level.[7]

Measured from the ground at its foot, Olympus Mons is taller. ESA has given 24 km and 26 km for its height above the surrounding plains.[4][5] NASA says it rises 27 km (17 mi), without saying from what level.[2] The figures differ mainly because they start from different places.

Olympus Mons vs Everest: how do they compare?

Olympus Mons’s peak stands about two and a half times as high as Everest’s.[1] Everest rises 8,848.86 m (about 29,032 ft) above sea level, the height China and Nepal announced in 2020.[8] That makes it the highest point above sea level on Earth, but not the tallest mountain from base to peak. That record belongs to Mauna Kea in Hawaii, which rises more than 10,210 m (33,500 ft) from its base on the seafloor, NOAA says.[9] Measured from its base, Olympus Mons is still more than twice as tall.

Mars has no sea level, so Olympus Mons is measured from Mars’s reference surface or from the plains at its foot. Everest from the 2020 China–Nepal survey; Hawaiian summits from the State of Hawaii; heights from the seafloor from NOAA and the National Park Service.[1][2][3][4][5][7][8][9][10][11]

How big is Olympus Mons?

About 600 km (370 mi) across at its base, an area NASA compares to the state of Arizona.[2][3] ESA has given 620 km (385 mi).[15]

At the top is a caldera: six overlapping collapse pits that together measure about 65 by 80 km (40 by 50 mi), according to a 2021 USGS geologic map.[12] It is about 3 km (2 mi) deep.[4][5] The pits formed when the top of the volcano sank as magma drained out of chambers underneath.[13]

The volcano’s edge is a steep cliff, the basal scarp, up to 7 km (4 mi) tall in places. Beyond it lies the aureole, a band of wrinkled ground left when the volcano’s lower flanks collapsed several hundred million years ago. The landslides piled up to 2 km (1.2 mi) thick, and some traveled more than 1,000 km (620 mi) from the peak, ESA says.[1]

How did Olympus Mons form?

From thousands of lava flows piling up in one place over a very long time. It is a shield volcano, like Mauna Loa in Hawaii: a broad mountain with rounded slopes, built by runny lava that holds little gas.[11][15] Layers in the caldera walls match the lava flows on its surface in thickness and width, which confirms that the volcano is built of many thousands of them.[13]

Mars has no active plate tectonics. On Earth, the plates of the crust slowly move, about as fast as fingernails grow.[22] On Mars, the crust where Olympus Mons first erupted never moved away from the source of the magma, so the lava kept stacking up in the same spot.[14] The hot spots inside Mars that fed its volcanoes lasted a very long time; how they survived so long is still unclear, ESA says.[15]

Data from ESA’s Mars Express show that Olympus Mons sits on a rigid outer shell, while its neighbors, the Tharsis Montes, partly sank into a weaker one.[17]

Is Olympus Mons the largest volcano in the solar system?

It is the tallest known. NASA calls it the largest and tallest volcano in the solar system.[3][7] The USGS puts it more carefully: Olympus Mons is “one of the broadest volcanoes and certainly the tallest in the Solar System.”[18]

A mountain on the asteroid Vesta comes close in height, and it isn’t a volcano. On Vesta, a huge impact left a basin called Rheasilvia.[20] The mountain in its middle is about 180 km (110 mi) wide and 20 to 25 km (12 to 15 mi) tall, NASA says.[19] On Earth, the largest active volcano is Mauna Loa, which makes up about half of Hawaiʻi Island.[11]

Is Olympus Mons still active?

Nobody knows; it may be dormant rather than dead. A 2004 study of images from ESA’s Mars Express found that the summit calderas of Olympus Mons and four other big volcanoes were active again and again over the last 20% of Mars’s history, “with phases of activity as young as two million years.” The authors said the volcanoes are “potentially still active today.”[16] Mars itself formed about 4.5 billion years ago.[3]

Those ages come from counting craters: a smooth surface with few craters is young.[15] The same study found glacier deposits at the foot of the escarpment as young as about 4 million years, and suggested that water ice may still survive under dust high on the volcano.[16]

What other volcanoes are on Mars?

Mars has the largest volcanoes in the solar system, and Olympus Mons is the tallest of them.[1] It sits at the edge of Tharsis, a volcanic region about 4,000 km (2,500 mi) wide that stands some 10 km (6 mi) above its surroundings.[14]

• The Tharsis Montes. Three giant volcanoes: Arsia Mons, Pavonis Mons and Ascraeus Mons.[15] They are about 470 km (290 mi), 370 km (230 mi) and 460 km (290 mi) wide.[21] Like Olympus Mons, their calderas were resurfaced within the last 20 million years.[15]
• Elysium. A second volcanic region, active on and off over billions of years.[15] One of its volcanoes, Elysium Mons, is about 400 km (250 mi) wide.[21]
• Hecates Tholus. An explosive eruption on its northwest flank about 350 million years ago left a caldera 10 km (6 mi) wide. Scientists had thought explosive eruptions were limited to Mars’s early history.[15]

The volcanoes are only one part of the Martian landscape. The surface of Mars covers the canyons, craters, dunes and ice caps around them.

Sources

1. ESA — Landslides at the foot of Olympus MonsPrimary · checked Oct 6, 2026
2. NASA — NASA’s Mars Odyssey Captures Huge Volcano, Nears 100,000 OrbitsPrimary · checked Oct 6, 2026
3. NASA Science — Mars: FactsPrimary · checked Oct 6, 2026
4. ESA — Olympus Mons Caldera RegionPrimary · checked Oct 6, 2026
5. ESA — Olympus Mons in close-upPrimary · checked Oct 6, 2026
6. NASA Planetary Data System, Geosciences Node — MGS MOLA Mission Experiment Gridded Data Records (MEGDRs)Primary · checked Oct 6, 2026
7. NASA Science (Photojournal) — Top of Olympus MonsPrimary · checked Oct 6, 2026
8. NPR — Mount Everest Gets Growth Spurt As China, Nepal Revise ElevationSecondary · checked Oct 6, 2026
9. NOAA National Ocean Service — What is the highest point on Earth as measured from Earth’s center?Primary · checked Oct 6, 2026
10. State of Hawaii DBEDT — State of Hawaii Data Book 2024, Table 5.13: Elevation of Major SummitsPrimary · checked Oct 6, 2026
11. U.S. National Park Service (Hawaiʻi Volcanoes) — Mauna LoaPrimary · checked Oct 6, 2026
12. USGS — Geologic Map of Olympus Mons Caldera, Mars (Mouginis-Mark, SIM 3470, 2021)Primary · checked Oct 6, 2026
13. HiRISE, University of Arizona — Lava Flows at the Summit of Olympus Mons (PSP_007959_1980)Primary · checked Oct 6, 2026
14. USGS Hawaiian Volcano Observatory — Volcano Watch — Volcanism on other planetsPrimary · checked Oct 6, 2026
15. ESA — Mars Express science highlights #5: Recent and episodic volcanismPrimary · checked Oct 6, 2026
16. ESA — Recent and episodic volcanic and glacial activity on Mars (Neukum et al., Nature, 2004)Primary · checked Oct 6, 2026
17. ESA — Olympus Mons topographyPrimary · checked Oct 6, 2026
18. USGS — Geologic maps of the Olympus Mons region of Mars (Morris and Tanaka, I-2327, 1994)Primary · checked Oct 6, 2026
19. NASA Science (Photojournal) — South Pole Vistas (Vesta)Primary · checked Oct 6, 2026
20. NASA Science — 4 VestaPrimary · checked Oct 6, 2026
21. USGS / IAU — Gazetteer of Planetary Nomenclature: MarsPrimary · checked Oct 6, 2026
22. USGS — How fast do tectonic plates move?Primary · checked Oct 6, 2026