Brief Description: When volcanoes erupt, magma is released from their interior. Magma is molten rock, concentrated in magmatic chambers. The magmatic chambers often remain sealed for millions of years between two eruptions, until the pressure is high enough to create an opening, a fracture on a weak spot on the layers of the surface of the Earth. Magma has the tendency to rise slowly to the upper layers of the crust of the Earth. In cases that large fractures go through the crust over the magmatic chambers, magma finds an outlet towards the surface. Mildly spurting or violently ejected, it goes out, cools off and becomes solid. If the magma is viscous, the gases cannot easily get away from the volcano. Therefore, the pressure increases until the gases find an escape passage violently. During the abrupt eruption of a volcano, gases are ejected, as well as magma, which flows in the form of lava or explodes and breaks into pieces that are called volcanic tephra. The sizes of tephra can vary from small particles of ashes to solid pieces of various sizes. The flow velocity of these pyroclastic materials can reach 160 km/h. Lava, namely the exiting molten magma, can be 10 times hotter than boiling water and destroys everything in its passage, as it flows like a river on fire. The eruption creates a crater, where lava, the other solid spurts and tephra form the volcanic cone.