Arsia Mons is 12 miles high and 270 miles wide, dwarfing Mauna Loa, Earth’s largest volcano, which is only 6.3 miles high and 75 miles wide, and mostly underwater. (It’s not the biggest volcano on Mars, though. That’s Olympus Mons, which is more than 13 miles tall and the largest in the solar system.)

Dr. Noe Dobrea said this was clearly not a volcanic event, because spacecraft would have detected a rise in methane, sulfur dioxide and other gases that spill out of eruptions. Instead, this is an example of how topography affects weather.

Meteorologists even have a term to describe this phenomenon: orographic lifting. “It happens on Earth a lot,” Dr. Eldar Noe Dobrea said, mentioning storms that frequently break out in the Sierra Nevada mountains in California.

The clouds form when water-laden air is pushed upward along a mountain. Cooler, thinner air cannot hold as much water, causing some of the moisture to condense and freeze, forming clouds. The air on Mars is much thinner than on Earth, but the rules of weather physics also apply there.