Some people have reported seeing so-called “ witch’s hair ” drifting in the air. These are fine, sharp, glassy needles that are formed in volcanic eruptions when lava droplets rapidly cool and stretch. Because they are light, these glassy fibers can travel long distances and can cause skin and eye irritations.

The concept isn’t hypothetical. Tephra layers in Icelandic peat cores show that eruptions soared six-fold between 12,000 and 10,000 years ago —exactly when