why do magmas rise toward the earth's surface?
<answer> The gas forms a separate vapor phase when pressure is decreased as magma rises toward the surface of the Earth. <context> Gases in Magmas. At depth in the Earth nearly all magmas contain gas dissolved in the liquid, but the gas forms a separate vapor phase when pressure is decreased as magma rises toward the surface of the Earth. This is similar to carbonated beverages which are bottled at high pressure.