Would a scenario be possible where an existing virus hybridizes with a still-undiscovered virus that previously lived only in geothermal features, such as deep ocean vents, geysers, mud pots, or volcanic craters, to form a dramatically life-threatening disease?
closed as too broad by Renan, Mołot, JohnWDailey, elemtilas, rek Oct 26 '18 at 3:51
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
You can get new virus from a vent, but very hard.
Viruses cannot live in water or mud, they have to live inside living creatures. Outside a living thing, viruses die fast.
"deep ocean vents, geysers, mud pots, or volcanic craters" are lethal to most living things. Creatures that live there are called extremophiles, and it will be hard for a conventional animal or human to get close enough to get infected.
Viruses do not hybridize, b/c they reproduce asexually, but tricking a host's cell into making a copy of themselves. They can mutate, and can get a strand of DNA from another virus if it infects the same cell: https://en.wikipedia.org/wiki/Virus#Genetic_mutation
For this recombination to happen, virus has to jump species between extremophile and conventional animal. Most extremophiles life is simple bacteria:
So you need a bacteria that can survive in both the vent, and in the new host. And the host that come close enough to a vent to get infected by bacteria, but survives. And the virus that lives on that bacteria, and can jump species to the host; this is problematic since all human viruses jumped species from verterbrates, not bacteria. B/c viruses kinda specialize on a species, or group of species. So it is very unlikely.
Maybe you can have your plague caused by the vent bacteria itself, not the virus. Maybe the bacteria mutates a human virus. Or maybe your patient zero contracts the mutating virus from a bat during the expedition to a geyser.