howdy everyone and welcome to video three of module two in the next three videos we're going to be focusing on the different types of plate boundaries but first we're going to talk about divergent plate boundaries because it goes very nicely with our idea of seafloor spreading now divergent boundaries are when we have two tectonic plates moving apart they're diverging they're splitting apart and these can occur between two continental plates where we have two continents splitting apart or more commonly between two oceanic plates where we have two oceanic tectonic plates splitting apart like our mid ocean ridges that's the most common type so most of our divergent boundaries are found at these mid ocean ridges now divergent boundaries are the process where those oceanic plates are diverging forming new ocean lithosphere known as seafloor spreading so that idea of seafloor spreading is all about our divergent boundaries now here's a graphic i love graphics hopefully you probably noticed that by now it really helps explain things better than listening to me talk or reading words on a screen but divergent boundaries are where we have those plates splitting apart they're moving in opposite directions and what happens when plates do that we're moving in opposite directions the lithosphere is moving in o opposite directions this is allowing that athenosphere that that hot mantle material to rise up because we're making accommodation space for that material to rise up and when that material rises up it's entering depths where there's less pressure so we have pressure decreasing because that material is moving up the pressure is decreasing and that actually causes melting because we're lowering the melting point when we decrease our pressure and that causes magma to form and this magma reaches the surface as lava and solidifies and cools and makes new rock makes new ignous rock it's making new oceanic crust oceanic lithosphere so it's forming it's forming new crust at these mid ocean ridges at this divergent boundary and that's because the plates are moving in opposite directions allows that hot mantle material from below to rise up melt form new oceanic lithosphere and this process is continuing so we're continually creating new oceanic lithosphere so it's pushing the older stuff out of the way so we have that continue motion divergent boundaries splitting apart now we can also have this in our continents it works the same way um but it's just most common in our oceans that lithosphere is thinner in our oceans so at divergent plate boundaries we see a lot of mid ocean ridges when they happen on continents we see continental ripped zones so here's probably the most famous example of a divergent plate boundary between oceanic and oceanic plates this is the midatlantic ridge so this is the middle of our Atlantic Ocean we're looking at a map of what the seafloor looks like and I don't think I have to point out to you where that boundary actually exists you can see it very clearly this is an underwater mountain chain and that's because right here we have our plates splitting apart that's allowing that hot mantle material to rise up melt form new oceanic crust which is really really hot hot stuff likes to rise up kind of forms our mountain chains as it's getting pushed away it's cooling down and when it cools down it becomes denser it starts to sink and starts to form lower and lower topography so that's why we have these mountain chains this is real hot new crust moves away gets colder colder and denser that's our mid-Atlantic ridge so here's just another graphic showing those mid mid ocean ridges and how they form the plates are splitting apart allowing that hot man's material to rise up melt form new oceanic crust is continually being pulled apart creating that mid ocean ridge and that's what's creating those beautiful colors that we saw in our seafloor map when we're looking at the ages the new crust is at the ridge the red colors gets pushed away the old crust the blue colors are near our coasts near the continents farther away now another example of a mid ocean ridge that is um easier for us to study because it's not underwater is Iceland iceland is actually sitting on top of the mid-Atlantic ridge so we can actually go there and study these divergent plate processes on land iceland's a little bit complex because it's also sitting on a hot spot which increases its volcanic activity but we won't get into that iceland is sitting on top of the Mid-Atlantic ridge and what do you know about Iceland well if you don't know anything about Iceland you can at least look at the photo there's volcanoes right so divergent plate boundaries have tons of volcanoes because we have the plates splitting apart here allowing that hot mantle material to rise up melt and form new oceanic crust so here at Iceland we're actually forming new oceanic crust and here's a map of Iceland showing you that it is indeed sitting on that mid-Atlantic ridge and Iceland is just a ton of oceanic crust that has built up so much over time that it's actually forming an island that you can actually walk on it's an island that's because we have a lot of volcanic activity there so the island is formed by the volcanoes themselves now a divergent boundary between two continents not as common but they do exist here on Earth and the most famous one the East African Rift and you can see Africa is actually trying to split apart even the Arabian Peninsula splitting away from the main continent of Africa forming a new ocean the Red Sea it's going to continue to get bigger and bigger but we also have East Africa um is splitting in multiple areas as you can see in this map and when two continents are splitting apart what's happening the same processes as when two oceans are splitting apart we have things being pulled apart it's being stretched allowing that hot mantle material to rise up in the form of volcanoes most famous one here is Mount Kilimanjaro mount Kilimanjaro is a volcano that is formed because the plates are splitting apart there so lot of um examples that we could see on earth of two d of of two plates splitting apart whether that be two oceans or two continents but what happens when they come together that's what our next video will be all about