GEology question!!!!!!!!!?

Water and other gases are locked in the oceanic crust. As the oceanic crust is subducted in an ocean-continental boundary, the immense pressure drives the water and other gases out of the rock and they travel into the resulting magma that is made. Water and various gases act as what are called volatiles, and these affect the composition of magma. The presence of volatiles generally makes magma less viscous and more violent. The gases bubble up and explode, creating especially violent volcanic eruptions.

So, the role of water and other gases is to act as volatiles and affect the composition of magma and the intensity of volcanic eruptions.

I hope this helps. Good luck with your studies!

The slab subducts into mantle rocks that are very hot, but still solid. Water coming off the subducting slab reduces the melting point of the mantle rocks, allowing some of it to become magma at that temperature. This magma then rises and may erupt at volcanoes.

scroll down to "Generation of Arc Magmas" for a more detailed explanation: http://myweb.cwpost.liu.edu/vdivener/notes/subd_zo...