How big is the largest volcano? On Mars it is as big as France!

Posted By on March 31, 2020

Olympus Mons is the tallest mountain and largest volcano on any planet in the solar system. It is about the size of France (or the U.S. state of Arizona) and is a shield volcano 624 km (374 mi) in diameter, 25 km (16 mi) high, and is rimmed by a 6 km (4 mi) high scarp. A caldera 80 km (50 mi) wide is located at the summit of Olympus Mons. To compare, the largest volcano on Earth is Mauna Loa. Mauna Loa is a shield volcano 10 km (6.3 mi) high and 120 km (75 mi) across. The volume of Olympus Mons is about 100 times larger than that of Mauna Loa. In fact, the entire chain of Hawaiian islands (from Kauai to Hawaii) would fit inside Olympus Mons!


Olympus Mons is the youngest of the large volcanoes on Mars. It and was likely formed during the Hesperian Period which lasted between 3,700 million years ago and 2,000 million years ago and has been known to astronomers since the late 19th century.

It’s a shield volcano (similar to the volcanoes than make up the Hawaiian Islands). Olympus Mons covers an area 300,000 km2 (120,000 sq mi), roughly the same size as Italy.

Finally, it has very gently sloping profile with an average slope of only .

Because of the size of Olympus Mons and its shallow slopes, an observer standing on the Martian surface would be unable to view the entire profile of the volcano, even from a great distance.

Similarly, an observer near the summit would be unaware of standing on a very high mountain, as the slope of the volcano would extend far beyond the horizon, a mere 3 km away.

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