Why do magmas rise toward Earth's surface? Why do magmas rise toward Earth's surface? Magmas are more viscous than solid rocks in the crust and upper mantle. Most magmas are richer in silica than most crustal and upper mantle rocks. Magmas are mainly liquid and contain dissolved fluids such as water; most are less dense than the adjacent solid rock. all of the above

most are less dense than the adjacent solid rock.

Explanation: Magma forms when rocks are heated and often occurs during volcanoes. It is almost in liquid form and contains such gases as water vapor. This means that it is less dense than surrounding rocks and the earth crust. Because the density is lower, it moves upwards and absorbs even more gas molecules as it does so. These bubbles expand and build up pressure which in turn helps the magma travel upwards until it bursts out from the earth surface.  

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