This is a question for geology people... Imagine an exoplanet with a thin crust, intense tectonic activity, but with weak, fragmented crust plates that buckle and sink as well as subduct beneath each other.
This generates volcanic islands constantly emerging above the sea level of the global ocean, but with sinking plates, these islands are pulled under as fast as new ones emerge. I'm thinking a turn-over rate on the order of centuries or millennia.
Human colonists can farm the nutrient-rich islands, but no stable population centers can truly establish themselves before the islands sink. Are there known geologic factors preventing this scenario, or would the heat necessary render the planet a molten pressure-cooker?