 This is the second video in the series on convergent plate boundaries, speaking about plate tectonics. This video is going to discuss ocean-ocean convergent boundaries. Now, in this scenario, you have two oceanic plates barreling towards each other, converging on each other, coming into a compression type stress situation. In this scenario, almost always, the younger and hotter oceanic plate will be the triumphant one, and it will not subduct. The young, old, cold ocean plate will be the one that subducts, and that's depicted here by two goats. I didn't have an old, cold goat picture. Some of the key features of an ocean-ocean convergent boundary are very similar to those of the ocean-continent convergent boundary. You get a deep ocean trench, a subducting plate, an arc of explosive volcanoes, and those are the main features that you see. Note again that as the ocean plate subducts, it brings with it water, that water is driven off by heat in the mantle, and then that water mixing with the mantle melts the mantle and creates the magma that is responsible for these island arcs in this case. These are also areas where you get very large earthquakes, some of the largest recorded. And these are earthquakes like we saw that caused the tsunami, the recent tsunamis in Japan and the Indian Ocean. Here's another more technical picture of the same scenario. A trench, here's your subducting plate, and notice the water being driven off the plate and generating that magma. Some other more technical features of this area is a back arc basin. As the plate subducts, it creates a realm of spreading behind the plate. You create a basin, a little secondary convection cell that you get in some cases. And of course the accretionary prism or wedge where that plate is smearing material onto the plate that is it is subducting below. Where's this happening? A great example of the Sumatran Islands. Notice all of these little volcanoes in the Indonesia area. Those are associated with a subducting plate. Another good example is the Aleutian Islands where you have the Pacific plate moving northward and subducting below the North American plate and creating this string, this arc shaped string of volcanoes along the tail of Alaska. Oceanic subduction. Here is the Mariana's trench and you can see it's one of the deepest features in the world. The deepest part of our ocean, right? 11,000 meters below sea level. This is caused by a convergent boundary, ocean-ocean convergence. You can see the arc-shaped volcanoes being created behind that boundary. There's a bathymetric ocean floor depth map. There's that trench and there's your volcanic arc. Based on how young and hot a plate is, that'll dictate how it subducts, right? In this image here you see an old cold plate being subducted and it subducts much more steeply. It's much more willing to subduct because it's hot or it's cold and dense and heavy and ready to subduct. As opposed to a hot and young plate, it's kind of forcefully subducted. It's still buoyant and upright, right? And it will subduct at a much more shallow angle. An example of an old and cold subduction is the Mariana's trench area. And I have a 3D view of the earthquakes from that subduction zone provided by the Iris website. So you go from the map view and if you look off to the side, you can see the profile of those earthquakes dipping quickly into the earth. And those earthquakes represent the trace of that subducting oceanic plate. Also with the hot and young scenario, like in the Peru area, you get a much more shallow subduction zone. And hopefully we'll be able to view the 3D view of the earthquakes associated with that subduction zone. Notice that these are not subducting, this plate is not going down nearly as quick. Notice that these earthquakes start out shallow and get deeper as you move in towards the subduction area. These are some of the questions you'll see on your homework. This is a classic, what's known as a bini off zone. It's a trace of earthquakes that represents the subducting plate. Plate starts subducting up here in the purple area and it's ducks deeper and deeper and deepest in these yellow and orange areas in this image. So that's your young and hot plate is your force type subduction. Your old and cold plate is your spontaneous type of subduction. What kind of happens on its own, sinking by its own weight. Okay, here's the third scenario is the continent versus continent. And again I'm going to stop here and pause the video and break this into small sections. So please do watch the third scenario video for the final part.