  A new approach to the volcanic eruption theory is proposed. It is based on a
simple physical mechanism of the imbalance in the system "magma-crust-fluid".
This mechanism helps to explain from unified positions the different types of
volcanic eruptions. A criterion of imbalance and magma eruption is derived.
Stratovolcano and caldera formation is analyzed. High explosive eruptions of
the silicic magma is discussed
