The halos are from almost optically perfect hexagonal prism ice crystals that slowly form downwind of snow cannons. The crystals grow on tiny seed nuclei emitted by the cannons. They are there to promote snow formation - Halo forming crystals are a splendid by-product.

This display - like others - is rich in Parry oriented crystals. We see a rare suncave Parry, even rarer helic arcs and Parry supralaterals.

There 'might' be a trace of upper and reflected Lowitz arcs.

The HaloSim ray tracing at left reproduces the halos. Those in Saskia's image are labelled in blue.