It may dwarf Earth's mountains and volcanoes, but Olympus Mons isn't very steep: it has an average slope of 5 degrees. It's part of the Tharsis region of Mars, where the volcanoes are all 10 to 100 times larger than the ones on Earth. Though it hasn't been active for millions of years, it's possible that it may erupt in the future.
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Key Facts In This Video
Olympus Mons is more than twice the size of Mt. Everest and five times as high as Earth's tallest volcano, Mauna Loa. 00:47
Volcanoes on Mars remained active 1,000 times longer than Earth's volcanoes. 01:48
Mars has a thicker crust and weaker gravity than Earth, allowing mountains and volcanoes to grow much larger without collapsing. 02:54