this post was submitted on 20 Apr 2025
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Worldbuilding

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I say "flying" instead of "floating" to differentiate what i'm talking about from islands that float on the sea (like Delos).

My world's flying islands are made of a kind of coral that grows up to tens of kilometers in size, usually smooth on the bottoms and with plant life on top, mostly from seeds left there by birds. The polyps excrete a gas lighter than air that keeps the colony afloat.

Islands drift with the wind and bob up and down as the coral gets dehydrated from being above the clouds and some of it dies, reducing lifting gas production and making the island sink until it becomes healthier again.

Today i wondered, what would happen if lightning struck one of these? What little i've read about lightning hitting airplanes and animals leads me to believe it wouldn't be great for the coral, but i'd love to hear what people who might know more about these things think.

Would the strike be less impactful with no ground current? Would the coral have to develop a way to avoid stormy areas? Would these things just being less conductive than air be enough to protect them, or would they need to develop something like a Faraday cage to be safe in a storm?

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[–] [email protected] 9 points 2 weeks ago

I'm only claiming layperson knowledge. I do not have a Biology or Physics professional background. I'm going to go less traditional here.

I'm going to say in this fictional world, the lightning strikes through the island. As in, a lightning bolt strikes from the high clouds to the island's surface, and then another bolt forming from the underside of the island striking down (potentially all the way to the ground). Since lightning in relativity is the equalization of electrical potentials between the clouds and the ground from moving masses of air, your flying island acts as a bit of a flying lightning rod. Its large enough (unlike a passenger jet) to act as a conductor for the ions of either charge.

Islands drift with the wind and bob up and down as the coral gets dehydrated from being above the clouds and some of it dies, reducing lifting gas production and making the island sink until it becomes healthier again.

When the island's altitude is low, the larger strike will occur on the top surface of the island. When the altitude is high, it will be a smaller strike on the surface, and much larger bolt extending from the underside of the island going down to the ground. Further, depending on the size of the bolt, and the exit point on the bottom, some coral will die. This can cause the island to list to one side until the coral is healed/replaced. You could even have perpendicular or temporarily upside down islands because of the uneven remaining distribution of coral polyps.

Another scenario: If an island is small enough, or a bolt of lightning large enough, near all (or all) coral dies in the lightning strike, and the flying island dies, crashing into the grown in a giant, loud, catastrophic event. Perhaps small colonies of coral polyps surviving a crash to the ground is also the the birthplace of future flying islands. The small amount of surviving coral is jammed deep underground in the island crash where it grows and reproduces over X period of time, eventually tearing a large amount of ground out with it as a new flying island joins the world.

You could even have characters weaponize this. Plant flying coral underneath the cities of your foes. Years/decades later, large sections of the city abruptly rip themselves out of the ground becoming islands and destroying large parts of the cities with it. This could be extended to societal laws preventing the import of coral into cities, with high penalties for doing so.

Lots of great possibilities for telling stories in this world:

  • warfare - governments using them as the equivalent of battleships as they fly over enemy towns and strike from above.
  • domesticating them for transportation
  • selective breeding programs for specialized corals with greater growth rate, higher lightning resistance, or increased lift with smaller size
  • religion surrounding the origins of the island or their reproduction
  • scarcity - the story of the people that find the last floating island in the world