It seems like ocean volcanoes grow pretty much uninhibited until they reach the surface, at which point they start to peter out. Why is this? I would think that the dense freezing ocean waters would have a much more cooling effect on lava than the thin warm atmosphere. On the other hand, I suppose the water could have some sort of buoyancy effect. What’s the scoop?
Uh, ever been to Hawaii? Those volcaoes didn’t peter out. Not sure your point. One can notice that there is relatively little in the way of erosion away from the water surface, so a subsea volcanoe will grow more rapidly underwater than shortly after it breaks the surface-is that the kind of process you are thinking about?
Peter out in height, not in activeness.
I’m not at all an expert, this is 100% speculation, but I’d think that the quicker freezing underwater would answer your question. In the open air, lava takes a longer time to freeze, so it has more time to spread itself thin. Underwater, it freezes quickly after coming out of the volcano.
Also, its possible that underwater, the fine particles and dust spewed out of the volcano quickly becomes part of the mountain, while it floats away in air. Not sure about that.
IIRC, the angle of repose of most materials decreases as the density of the surrounding material increases. This’d make a volcano spread out more under water than it does above the surface.
that is an interesting question. Since volcanology isn’t something I have studied, I can’t help. It does seem that a volcano forming over a hotspot (as in Hawaii) has the potential to grow higher than one forming at a subduction zone, but I don’t know why.
The OP did encourage me to find some great photos of volcanoes though:
http://volcano.oregonstate.edu/ikonos/index.html
It has to do with tectonic plate movement and the volume of cones as they get taller. Hot spots were mentioned earlier. These are spots in the crust where, or various reasons, the lava can seep through. In Hawaii, as the Pacific plate moves, new volcanoes form. The extinct volcanoes at the northwest edge of the island chain are much older, and therefore more eroded, than the Big Island at the southeast edge of the chain. Eventually the spot where a volcano is forming moves away from the hot spot and no more lava gets through to add to the existing cone.
Southeast of the island of Hawaii there is a new volcano forming deep underwater. When it hits the surface of the water (assuming it does) it will be the next island in the chain.
The other reason the growth peters out is the volume of fresh material needed to add to an already tall volcano. Think of how much dirt you need to raise a pile from 30’ tall to 40’. Then compare how much more you would need to raise it from 100’ to 110’. It is a lot more because you need to add all the material to build up the sides. Most ocean volcanoes are several thousand feet tall. It takes a lot of material to make it a little taller and in the meantime the vent closes for one reason or another (such as a moving plate).
So, it has nothing to do with the volcano being exposed to the air. It has everything to do with the size of the volcano and activity of the vent.
Oh, and many volcanoes don’t reach the surface. These are sea mounts or similar type features.