Lightning can superheat sandy ground fast enough to melt and fuse the grains into glassy tubes called fulgurites. These usually form underground and can look like twisted, brittle, hollow roots made of glass.

What’s happening

A lightning bolt carries intense heat and energy, and if it hits sand rich in silica or quartz, the sand can briefly melt and then cool into glass. The strike often leaves a branching tube or tunnel through the sand rather than a smooth lump on the surface.

What it looks like

  • Hollow or partly hollow glass tubes.
  • Dark, rough outer surfaces with glassy interiors.
  • Branching shapes that follow the lightning path.

Why it’s rare

The conditions have to line up just right: the sand needs to be the right composition, and the strike has to be strong enough and hit in a way that lets the heat travel through the ground. That’s why fulgurites are interesting natural finds, not something you see after every storm.

Safety note

Fulgurites are a sign that lightning can violently alter the ground, so beaches and dunes can still be dangerous during storms even if the result looks beautiful afterward.

TL;DR: lightning hitting sand can melt it into glassy, tube-like structures called fulgurites.