Question

When do we say that the volcano is erupted​

Answer 1

Answer:

Most volcanoes provide warnings before an eruption. Magmatic eruptions involve the rise of magma toward the surface, which normally generates detectable earthquakes. It can also deform the ground surface and cause anomalous heat flow or changes in the temperature and chemistry of the groundwater and spring waters. Steam-blast eruptions, however, can occur with little or no warning as superheated water flashes to steam.

Notable precursors to an eruption might include:

An increase in the frequency and intensity of felt earthquakes

Noticeable steaming or fumarolic activity and new or enlarged areas of hot ground

Subtle swelling of the ground surface

Small changes in heat flow

Changes in the composition or relative abundances of fumarolic gases

Answer 2

Hello friend!

Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Since it is lighter than the solid rock around it, magma rises and collects in magma chambers. Eventually, some of the magma pushes through vents and fissures to the Earth's surface. Magma that has erupted is called lava.