siberian spruce trees in finland’s riisitunturi national park become covered in a hard rime known as tykky as supercooled water droplets in fog freeze to the windward side of their branches. some trees can collect as much as four tonnes of this white ice, which is less dense than the familiar clear ice. photos by (click pic) pekka koski, rafael rojas, jarmo manninen, sven zacekniccoló bonfadini and hanneke luijting