4.100 billion planets: how many with active volcanoes? What planetary properties

Question

4.100 billion planets: how many with active volcanoes? What planetary properties (e.g., size, distance from the sun, rotation rate, age) control whether a planet is likely to have active volcanoes? What material properties (thermal conductivity, phase change behavior, density, "Q") are also important? Using all your important variable, describe the most volcanically active planet you can imagine. Hint: the lists above are not necessarily complete, nor does every item in the lists really matter. (Note: don't consider tidal heating for this question.)

Explanation / Answer

Volcanoes erupt when underground molten rock, or magma, finds a path through the lithosphere to the surface. Magma rises for two main reasons: First, molten rock is generally less dense than solid rock, so it has a natural tendency to rise. Second, a magma chamber may be squeezed by tectonic forces, driving the magma upward under pressure. Any trapped gases expand as magma rises, sometimes leading to dramatic eruptions.

The structure of a volcanic flow depends on the viscosity of the lava that erupts onto the surface. The rock type known as basalt makes relatively low-viscosity lava when molten because it is made of relatively short molecular chains that don't tangle with one another. Temperature affects lava viscosity as well: The hotter the lava, the more easily the chains can jiggle and slide along one another and the lower the viscosity. The amount of water or gases trapped in the lava also affects viscosity. Such materials can act as a lubricant, decreasing the viscosity of subsurface magma. But when lavas erupt, materials such as water may form gas bubbles that increase the viscosity.

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