Hair ice formation

Settled in 2015 by Gisela Preuss, Christian Mätzler, Diana Hofmann.

The meteorologist and polar explorer Alfred Wegener first proposed in 1918 that a fungus might be responsible for shaping the fine, silky ice filaments called 'hair ice' that appear on damp, rotting wood in winter forests, but the idea went untested for nearly a century. In 2015 Hofmann, Preuss and Mätzler identified the wood-decay fungus Exidiopsis effusa as present on essentially every sample of hair-ice-producing wood, and showed experimentally that sterilizing the wood with heat or fungicide reliably suppressed hair-ice formation, while reintroducing the fungus restored it. This confirmed that the fungus recrystallizes and shapes the ice into stable hair-thin filaments, likely by secreting compounds that inhibit ice recrystallization, directly validating Wegener's original biological hypothesis.

A forgotten hunch by the same scientist who proposed continental drift turned out, a century later, to be exactly right about a delicate winter ice sculpture grown by a fungus.

Explanations that circulated

• Hair ice forms from purely physical ice-crystal growth in wood pores with no living organism involved — the 2015 study confirmed Wegener's century-old hunch that a specific fungus is required: heat-treating or applying fungicide to hair-ice-producing wood suppressed the ice formation, while untreated wood with the fungus present kept producing it.

References

• Evidence for biological shaping of hair ice, D. Hofmann, G. Preuss, C. Mätzler, Biogeosciences, 2015