So imagine something (lava, nucular, magic, idk) permanently heated a small section of the ocean. I'm thinking hot enough that a person would die instantly of heatstroke if they fell in or were on the shore (maybe like 160F/70C?). The surrounding water and air should be relatively normal. I would imagine that the hot water would evaporate much faster than the normal water creating a big pillar of steam/fog. This would cause updrafts of air. I would also imagine that there would be a rather strong inward current as the cold water fills the space left by the evaporating water. Because of all the steam and fog I could think there would be a lot of rain as well. Do these assumptions seem reasonable or is this totally impossible? Now suppose there there were massive pillars of rock sticking up out of the ocean with people living on top. They couldn't get off the pillars because if they went down to sea level they'd die of heat. I'm trying to figure out how high they would have to be to have a temperate or tropic climate. would the rain give them enough water to survive? Also, how high do you think they would have to be to be above the fog? Sorry for this really rambling question... any thoughts of advice would be wonderful!
This exists in the real world, albeit on a smaller scale than I think you are describing or shooting for. Lava boiling the ocean has been a regular event on the coast of Hawaii and also of Iceland during modern times. This part of your question confuses me as to the scale of boiling ocean you are wanting to describe. This sounds like quite a bit larger area of boiling to make the pillars both large enough to be habitable and also encompass the concern for the boiling water below.
A better answer to these questions, are more questions. More specifically about what exactly caused the ocean to boil--even if its some magic spell, there must be some causative agent at play e.g. the core of the Earth is heating up, causing the oceans to boil, because of the water being directly heated by a flame thingie, radiation, etc. When you know what's the causative agent at play, you have a better chance of deducing what might happen. Yes, rising steam from a boiling ocean could possibly result in clouds and rain, also would cause possibly hurricanes as there would be lower pressure inland and higher pressure above sea. But this is assuming we're not in a plain area--for instant, where I live, in spite of very high temperatures (up to 50 degrees Celsius) there is low precipitation; I can't find the correct terminology for it, you'd have to consult a good Geography book for it. Steam would also affect the humidity, which can have undesirable effects on crops and animals regardless of rain--might even cause decay of food and material objects. Also, I'm not sure how pillars rising from the ocean floor correlate with, well, boiling water. Again, the causative agent matters--is it just the tectonic plates going nuts, or is there actual physical manifestation of matter which previously did not exist? What kind of stone/rock is to not be heated up by boiling water? Can it float over water? Is it malleable/ductile? I recommend reading up some geography, especially regarding the layers of Earth, the tectonic plates and earthquakes, and other features which could cause such an incident. This is, if you're trying to be very scientifically accurate--otherwise, just wing it and worry more about the story itself!
Oh cool, I'll look into the Hawaii and Iceland thing! yeah, sorry I didn't make that quite clear, I'm thinking about a rather large bit of ocean, maybe 75 miles (120 km) in diameter. The pillars would also be quite large, 5-15 miles (8-25 km) across, big enough for towns, farms, and the like.
Wow, that's a lot to consider, thank you!! Currently I think I'm going with something like the steam vents at the bottom of the ocean. I think this should be okay for the rocks since rock melts at a way higher temperature than water boils/people would die. I suppose this might somehow make the pillar islands unstable but I unfortunately don't know too much about geology. I'll try to find out. For the pillars I'm sort of picturing islands with really tall cliffs, like these but bigger and further off shore http://freeyork.org/travel/the-most-spectacular-sea-cliffs I figured there could have been volcanic islands and the sides wore away or something similar? I hadn't thought of the humidity at all... That might actually be a big problem. I'll have to do some research.
As you have it now, what you describe isn't physically possible. For water at the surface of the ocean to be that hot, the temperature at the bottom of the ocean would have to be very large. For reference, the boiling point of water at 6000 m below the surface is around 500 degrees C. As the bubbles rise, they're cooled rapidly by the surrounding water, which is why you would need a very hot surface at the bottom of the ocean to cause boiling at the surface. However, you mention magic as a potential source, and that could easily work.
Hawai`i is similar to what you describe but much calmer. Assuming this is a fantasy think super-volcano such as Yellowstone National Park submerged and a lot more active. When a volcano erodes into the ocean it can become an atoll such as Bermuda, the island portion is the top of the old volcano, if it becomes submerged it gets covered by coral, Bermuda's case. So super-volcano that is still somewhat active, the ocean water can only leak in, such as high tide, large waves, lava tubes, etc. and is boiled off, geysers such as Yellowstone come to mind. The resulting steam bath can be toxic and could surround the exposed portions of the volcano making descent impossible. For example the ring of the volcano could be severely fractured down close to sea level, allow the boiling sea water to escape to the open ocean but the top edges are below the resulting cloud. BTW the boiling action could be submerged and the gas bubbles rise to the surface without it actually bringing the water temperature all the way up to a full rolling boil.
Hmmmm. This sounds really hard to make work plausibly but a really fun setting to read, so you must make this work! I think the Yellowstone hotspot idea has some merit as a heat source although it would have to be bigger and hotter, and the water would have to be relatively shallow. One idea would be to make your "ocean" a large shallow inland sea about the size of the Caspian, that's actually a giant crater lake inside the post-eruption caldera of a supermassive supervolcano. This would also have the effect of making your water very, very salty, and it would limit somewhat the cooling effect from the water if it's surrounded on all sides by land and the bottom is essentially a giant hotplate. Not sure it would actually work but it's a start. Although to keep the lake full you'd need massive inflow from rivers. One other idea is that you could heat it using the planet's Sun. I read a book once with a "rim world" where one side of the planet always faces the Sun and one is permanently dark. As on our planet Mercury, the light side of that planet is too hot for life and the dark side is a deep freeze. In the rim world model you have an Earthlike planet in such a situation where life exists only in the "rim" of permanent twilight where the two sides meet. Expanding this to your boiling needs, you might be able to construct a rim world that is heavily glaciated on the dark side , or even underground oceans that are slowly flowing like lava toward the light side as the edges slowly melt into slush and then flow downward and boil and evaporate as they hit the light...and your setting would be in the zone where the water is getting really hot before it evaporates into the sun. Granted I can think of a lot of reasons this probably wouldn't work - namely how to get enough ice to feed a flowing boiling ocean and replenish the ice supply
Also a quick thought on generating the requisite amount of volcanism is tidal friction. This is what causes massive volcanic activity on Jupiter's closest moon Io. The gravitational pull of the planet squeezes the moon's innards to the point where friction makes them melt. So if you set your story on an Io type moon of a gas giant you can have lots of ridiculous volcanic activity that might results in boiling lakes.
