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Pladetektonik - geologiske karakteristika for konvergerende pladegrænser

Video transskription
We've already talked a lot about plate boundaries where essentially new crust material is being created and the plates are actually moving apart - we call these divergent boundaries, and the example we showed of this was the Mid-Atlantic Ridge where essentially new crustal material is being created. Now, on the other side of the equation you have areas where plates are ramming into each other. We see that over here where the Nazca plate is running into the South American plate. We see it over here where the Pacific plate is running into the Filipino plate - they're running into each other. So what happens over there? So what we're gonna do is just go through the different scenarios. The general idea is that one plate is going to get subducted under another. Tthey're ramming into each other, one is going to get essentially pushed under the other one. This diagram shows some subduction over here. Tthis is essentially an oceanic plate being subducted under another oceanic plate, so not too different than what might happen when the Pacific plate runs into the Filipino plate right over here, then on this side of the diagram we see an oceanic plate and the oceanic crust getting subducted under a continental plate, right over here. And this is what's happening when the Nazca plate is getting subducted under the South American plate and when that happens you have a couple of things so you have the oceanic plate being pushed under and what happens at the same time the continental plate gets pushed upwards causing mountain ranges like The Andes and that's exactly what causes - what has created The Andes, it's the upward force from the Nazca plate being pushed under the South American plate at that coast line. And what you're also going to see is, and if you can imagine you have these huge plates grinding past each other, it's not a very smooth process, every now and then you reach a breaking point where hug amount of energy get released so you're also going to see a lot of earthquakes in those areas and we know that Chile has a lot of earthquakes. And then on top of that, this is going to result in a lot of heat and a lot of friction of the plates grinding past each other essentially allowing magma to form at that part of the rock and because it's getting so heated you also have volcanoes in these areas where essentially something is being subducted underneath a continental plate. Now, we also talked about what's happening in the Pacific where we have the Pacific plate being subducted under the Filipino plate. That's what we keep referring to over here. And that's doing a couple of interesting things. So whenever you have subduction, you have trenches. But it's most interesting - or at least in my mind that the deepest trenches have been created where you have an oceanic plate being subducted under another oceanic plate. So a couple of things are going to happen. You're going to have deep trenches form, over here you see in this diagram we also have a trench and the first example, but you have trenches form where one oceanic plate is being subducted under another and then you have that same type of friction that you saw over here create volcanoes and those volcanoes will initially be underwater volcanoes since these are both oceanic plates, or we're dealing with oceanic crust at that point of the plate, it doesn't have to be entirely and oceanic plate, and there'll first be underwater volcanoes but as the lave piles up and hardens, it'll eventually turn into a group of islands. And we've had that happening where the Pacific plate runs into the Filipino plate and first we have the trench, let me just draw everything right here. So, this is the boundary, roughly, roughly speaking this is the boundary between the two plates the Pacific plate and the Filipino plate right over here. And where it's being subducted you have the Mariana Trench which is the deepest trench in the world! It goes down 11 km - eleven thousand metres! That's deeper than Mount Everest is high. Mt Everest is about 9,000 metres high. And we'll see that's also due to another convergent plate boundary, another plate boundary where plates are running into each other. So not only do you see the Mariana Trench here because one plate is being subducted under the other, you see the formation of the Mariana Islands which were essentially created from underwater volcanoes because of all of the energy being released. And this is actually a depiction of what's the subduction that's happening at the Mariana Trench. You have the subduction over here then you have the Mriana Islands being created by essentially the enrgy causing magma and lava, essentially magma before it surfaces, to flow on the top and as lava just goes and starts building these islands. Now, the last type of convergent boundary is when you have two parts of continetal crust running into each other. So that's the situation that we have when the Indian plate is running into the Euroasian plate, I think you might already guess what's going to happen there. When you have two pieces of continetnal crust running into each other, one is more or less dense that the other. And so at least the crustal portions on them are just going keep jamming into each other. And so they're just going to push things up. This is a depiction righ here that I got from the USGS. And what's kind of depicting it - this is the Indian plate, this is the Euroasian plate, this is if you rewind a good bit before they really had the chance to jam into each other. But as they're jamming into each other, the Indian plate is kind of digging in a little bit, not being fully subducted, and it's causing the land to rise. And that essentially ends up with something like the Himalayas. This right here is a picture of Mount Everest which is almost 9,000 metres high, 9,000 metres above sea level. So, it's almost as high as the Mariana Trench is deep.