As volcanoes actually erupt

English scientist Matthew Jackson proposed a new scheme of how volcanic eruptions occur.

Now, most volcanologists agree that earthquakes are caused by processes that occur inside huge magma chambers. But there is another opinion: inside volcanoes – not huge caves of red-hot lava, but something like “volcanic porridge with lumps”. According to this theory, small lava tanks are sandwiched between solid rock fragments.

Previously, such a theory had already been rejected, because if the eruptions had taken place according to this scheme, there would have been much more samples of rock and crystalline components in the lava. But Matthew Jackson of Imperial College London gave an explanation for why this is happening.
 
Magma, being less dense than a rock, can rise through crevices and pores between pieces of rock. Capturing fragments and crystals, magma dissolves them. Thus, only hot liquid comes to the surface. It is precisely small magma reservoirs sandwiched between solid rock that provoke eruptions.