Okay, I've been posting for only a short while, but I was thinking of asking this question, based on the answer from the FAQ.'
"A: The Earth is thick enough to have a core of molten lava. Once there's too much of it in too confined a space, it finds its way out, just like the water will come out of a full bottle if you squeeze it too hard"
First, the core is not composed of "molten lava". There is solid proof that the core is solid, since it is so dense. The outer core is molten.
Second, that does not apply for andesitic volcanoes (those with sharp slopes). Neither does it apply for mid-ocean ridges, where oceanic crust is created.
The rock erupted by andesitic volcanoes, or stratovolcanoes, or any other kind of volcano, is identical to that certain type of volcano. For instance, the shield volcanoes of Hawaii erupt quite silica-poor basalt, whilst Vesuvius in Italy erupts silica-rich to intermidate material.
Now, the Hawaii shield volcanoes are the result of "hot spots", rising plumes of magma. That might rougly be explained by the FE answer above. However, the stratovolcanoes are the result of subduction, where one plate dives beneath another plate until it melts. The molten material then rise to the surface where it erupts in the form of volcanoes.
Subduction can be proven. There is no "subduction-free" theory that explains why the deep-sea trenches are located so closely to stratovolcanoes, or why stratovolcanoes erupt ash and debree that contains some amounts of water. Water which was "trapped" in the sediments of the diving plate - and then erupted again in the form of steam.
Also, if the flat earth "cylinder" has a bottom, then that area would have cooled - due to the surrounding temperatures. In case the cylinder is pushed forward, the centre of the cylinder would be squeezed. This would indeed cause some magma to be pushed upwards, but due to the two effects of acceleration (the upper side being pushed down) and push (the bottom side being pushed upwards), the magma could go in any direction. That would result in volcanic eruptions on the bottom side of the cylinder as well, and most likely earthquakes. These earthquakes would have been detected long ago, since they would be able to travel through the mantle to our side. If the cylinder is being pulled, then all the molten rock would simply "fall off".