Welcome class to lesson number 3 of our second quarter of Earth Science. In this video, I will talk about magma formation. In the last video, we discussed about the Earth's internal heat.
So this heat have resulted in the existence of different processes happening in our planet. And one of this is magma formation. Now, magma is defined as a molten or partially molten rock which is stored under the earth's surface and if this reaches the surface then it will be called or referred to as lava special conditions are needed for a magma to form so aside from the presence of the needed material which is the rock itself the following are also needed first one is the decrease of pressure that happens to our mantle and to the crust. Next, the addition of volatile materials to hot rocks and the transfer of heat from magma that is rising from the mantle into the crust. So there are three special conditions needed for the formation of magma.
Now, two processes are referred to when we are talking about magma formation the first one is decompression melting so decompression melting it is the process of creating magma by the reduction of pressure at a constant temperature in essence constant temperature is high but magkakaroon ng pagbabago, bababa yung pressure. So instead of the material constantly in solid form, dahil bumaba yung pressure, magkakaroon ito or magbabago ito into liquid or a semi-liquid. Next naman is flux melting.
So this occurs because of the introduction of volatile materials. So this volatile material could be water or a hydrous mineral. So in this case, it will cause chemical reaction to the hot rock which will turn this rock into or will melt this rock and will make it turn it into liquid or a semi-solid.
Magma formation is common in the following locations. So here in the rift valley, in the oceanic or mid-oceanic ridge, hot spot or mantle flumes, and in the subduction zone. This one is also a subduction zone.
So now, in the rift valley, what happens is decompression melting. In a sense, while the two continental crust, the pressure here decreases. So as this pressure is decreasing, the rocks which is in solid form will turn into molten rocks which will be called or referred to as magma. Same thing is happening to the oceanic or the mid-oceanic ridge.
The compression is happening so as the two oceanic crusts are diverging uh the decompression occurs, the pressure decreases and then magma is forming. As for the hot spot, the idea of the hot spot is that directly the heat that will produce magma comes from the mantle. So unlike our What happens here in the mid-oceanic ridge is that the heat source is deeper in the hot spot. So, it's more direct, which will directly, because of this heat, because of the increase in temperature, there will be magma formation.
And of course, there is still a little decompression melting that is happening. Now, subduction zone. In the subduction zone, the common is flux.
melting so while the oceanic crust is subduing, the oceanic crust goes down under a continental crust the water is introduced under our earth. So as water is introduced, the hot rocks will be melted because of flux melting, which will in turn form magma. Now let us identify the reason why and how magma rises.
First one is the density contrast. So magma rises faster when the difference in density between the magma and the surrounding rock is greater. Naturally kasi ang magma natin is less dense as compared to the rocks present in our crust and mantle. Pero kapag mas higit, mas malakas, yung difference ng density between the two materials mas mabilis. magma will rise from under our planet.
At deeper levels, magma passes through mineral grain boundaries and cracks in the surrounding rock. So, gradually, it will try to seep through these cracks. Now, when enough buoyancy and mass, it means that the amount of magma is enough and it is also buoyant, but it is not enough.
masyado nang mataas yung difference ng density ng rock layers and magma, then there will be no choice kundi tumaas yung magma. It will rise. Now, depending on the surrounding pressure and other factors, the magma can be ejected to the Earth's surface or rise at shallower levels.
So kung wala namang obstruction na mayayari at tuloy-tuloy yung difference between the density of the rock layer and the magma then ideally it will reach the surface of our planet but if there is a similarity in the density of the rock layer and magma the idea is that the magma will just stay in here under the crust so this is the same with what i am saying earlier so if there is no difference in the density then the magma will just stay there underneath a rock layer and it will solidify another reason kung bakit nag-re-rise ang magma natin is that because of viscosity so viscosity is referred to as the fluids resistance to flow so magmas with low viscosity flow more easily than those with high velocity and temperature silica content and volatile content control the viscosity of magma if there is an increase in temperature silica content and volatile materials viscosity will be altered If temperature increases, viscosity of the magma decreases. Meaning, mas magiging malabnaw yung ating magma, mas mabilis magpo-flow ito from underneath going to the surface of our planet. If there is more silica content in a magma, there will also be an increase in the viscosity.
Meaning, mahirapan ito mag-flow sa planeta or sa surface ng planet natin. And... If there is more water, dissolved water, in magma, then lesser on viscosity, it will flow faster on our planet.