phreatomagmatic

As a noun taxonomy

is the science or the technique used to make a classification.

As an adjective phreatomagmatic is

pertaining to a volcanic eruption caused by magma coming into contact with water.

As a noun water

is a chemical, found at room temperature and pressure as a clear liquid, having the formula H₂O, required by all forms of life on Earth.

As a verb water

is to pour water into the soil surrounding (plants).

As an adjective phreatomagmatic is

pertaining to a volcanic eruption caused by magma coming into contact with water.

In geology terms the difference between magma and phreatomagmatic

is that magma is the molten matter within the earth, the source of the material of lava flows, dikes of eruptive rocks, etc while phreatomagmatic is pertaining to a volcanic eruption caused by magma coming into contact with water.

As a noun magma

is the molten matter within the earth, the source of the material of lava flows, dikes of eruptive rocks, etc.

As an adjective phreatomagmatic is

pertaining to a volcanic eruption caused by magma coming into contact with water.

As a noun eruption

is a violent ejection, such as the spurting out of lava from a volcano.

As an adjective phreatomagmatic is

pertaining to a volcanic eruption caused by magma coming into contact with water.

As adjectives the difference between volcanic and phreatomagmatic

is that volcanic is of or pertaining to a volcano or volcanoes; as, volcanic heat while phreatomagmatic is pertaining to a volcanic eruption caused by magma coming into contact with water.