-as rock it heated and melts, it expands and becomes less dense

-low density material will always tend to float on top of denser material

-gases are much more bouyant than magma

-all magmas contain gases

-pressure increases with depth in the earth's crust due to the weight of overlying rocks

-at high pressures, deep in the crust, these gases are dissolved in the magma

-as the magma starts to rise up towards the surface there is less pressure on the magma and the gas separates from the magma as bubbles

-driving forces for making magma rise(buoyancy and gas content of the magma

-temperature of magma (high temperatures needed to melt country rock above)

-presence of cracks for magma to intrude along

-viscosity of magma( the more viscous the slower it will rise

-geothermal gradient (as the rising magma comes into contact with colder and colder rocks it will cool and become less denser and more viscous)

-rate of magma ascent (if magmas is forced up through the crust very quickly then it may get all the way to the surface before the cold country rocks have time to cool it down and make it crystallize

-a body of magma which has forced itself into surrounding pre-exisiting rock

-a body of igneous rock which when in magmatic state forced itself into surrounding pre-existing rocks

dike

a tabular discordant intrusive structure

(discordant means that the body cuts across any layering in the country rock)

-upward movement of a body of magma by fracturing of overlying country rocks

-magma engulfs the blocks of fractures country rock as it moves upwards

-the process by which magma melts country rock and assimilates the newly molten material

- ions originally making up the country rock are mixed in with the magma