# Arsia Mons water ice cloud formation on Mars > Developing situation record from CLSTR: https://clstr.news/situations/arsia-mons-water-ice-cloud-formation-on-mars > Updated: 2026-10-31T23:13:30.000Z. Sources: 2. Developments: 2. 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 indicates the cloud forms through ‘homogeneous nucleation’, a process where water vapor freezes directly into ice crystals without the need for dust or pollution particles. The phenomenon is triggered by the 20-kilometer-high volcano Arsia Mons. As winds strike the mountain, they are forced upward, causing air pressure and temperature to drop rapidly. This creates extreme atmospheric supersaturation, with moisture levels reaching 100,000 times higher than average conditions on Earth. This environment enables the spontaneous formation of ice crystals, which appear during the Martian spring and dissipate as the sun warms the atmosphere. NASA has observed the formation, noting that its 1,500 kilometer scale and specific composition challenge existing meteorological models. The organization of these crystals into such an extensive trail suggests that current scientific understanding of Martian weather patterns may require revision. ## Timeline ### 2026-10-31: NASA observes 1,500 km ice cloud on Mars NASA has identified a 1,500 km long water ice cloud on Mars, named AMEC, which is challenging current meteorological models. 2 sources. https://clstr.news/cluster/nasa-observes-1500-km-ice-cloud-on-mars ### 2026-10-17: Arsia Mons volcano triggers massive 1,800 km cloud on Mars Scientists have discovered that Mars' massive 1,800 km Arsia Mons cloud forms via homogeneous nucleation, where water vapor freezes into ice without needing dust particles to act as nuclei. 4 sources. https://clstr.news/cluster/arsia-mons-cloud-formation-explained-by-scientists --- Cite as: Arsia Mons water ice cloud formation on Mars. CLSTR, https://clstr.news/situations/arsia-mons-water-ice-cloud-formation-on-mars