Maria Popova (Member 38,823) witnessed this stack of smooth, lens-shaped clouds perched over the snow-capped peak of Volcán Lanín from the town of Curarrehue, Araucanía, Chile. The cloud is Altocumulus lenticularis duplicatus, which is formed by stable winds cooling as they rise to flow over mountainous terrain. The duplicatus part of the classification refers to the cloud’s laminated appearance, which develops if the airflow consists of alternating moister and drier layers. It is also described as a cap cloud when the cloud forms, like Maria’s, directly on top of the peak rather than downwind of it.

‘Under its sombrero of cloud,’ Maria wrote, ‘the volcano Lanín straddles the border between Argentina and Chile – a dramatic reminder that this rocky planet was shaped into a living world by immense tectonic and atmospheric forces that render all human-drawn borders and nationalisms senseless and sad: a tear in the eye of eternity.’