The news outlets are also starting to fill us in on basic plate tectonics, including Iceland's unique position directly upon a spreading ridge. One basic fact of plate tectonics is that volcanoes and magma and eruptions are not forced out of the Earth. Lava melts when the pressure upon it is relaxed. Volcanism emerges where the crust is being stretched apart, allowing lava to form and rise, by buoyancy, to the surface.
The motive force of plate tectonics is the sinking of cold crust. That causes two kinds of stretching, or extension. The first kind of extension is what we see at the opposite end of the plate, in Iceland, the midocean ridges, and a few other places like the African Rift and the Salton Sea. The analogy is two bedsheets stuck together by static clingas you pull them apart, the sparky place in the middle is where the midocean ridges and eruptions (and Iceland) are. (But remember that in the real Earth the bedsheets, the plates, are actually created at the ridges.) This kind of extension happens at the opposite end of the plates.
The second kind of extension happens at the same places where the cold plates (which geologists call slabs) sink. The motion of a sinking (subducting) slab is not like water going over a fall, although there is a degree of forward motion. There's also a degree of straight-downward motion of the sloping slab that stirs the underlying soft rock of the mantle. On the downward-facing side of the slab, the mantle is compressed, and on the upward face it is extended. So if you picture the west side of South America, the Pacific mantle is being pushed westward and the South American mantle is being sucked westward, along with the continent on top of it. That extension allows the volcanoes of the Andes to form, fed by the water and rocks of the slab beneath it. (Edit: A commenter corrects me about the Andes; the volcanoes of the Aleutian Islands are a better example.) That's why the volcanic "Ring of Fire" surrounds the Pacific. This kind of extension is directly associated with subduction, which accounts for nearly all of Earth's volcanoes on land. But not Iceland.