Arsia Mons volcano triggers massive 1,800 km cloud on Mars

Researchers have identified the mechanism behind the Arsia Mons Elongated Cloud (AMEC), a massive water-ice formation on Mars that can stretch up to 1,800 kilometers in length.

A study published in Nature Geoscience by a team from Sorbonne Université, including Jorge Hernández-Bernal and Franck Forget, reveals that the cloud forms through a process called ‘homogeneous nucleation’. Unlike typical cloud formation on Earth, which requires condensation nuclei such as dust or pollution, this process allows water vapor to freeze directly into ice crystals without any particles.

The phenomenon is triggered by the 20-kilometer-high volcano Arsia Mons. As winds hit the mountain, they are forced upward, causing a rapid drop in air pressure and temperature—falling by approximately 30 degrees Celsius within ten minutes. This creates extreme atmospheric supersaturation, with moisture levels reaching 100,000 times higher than average conditions on Earth. This intense environment enables the spontaneous formation of ice crystals, creating the massive cloud that appears during the Martian spring and dissipates as the sun warms the atmosphere.