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Video transcript

we've talked a lot about the formations of mountains and volcanoes when plates are running into each other or one plate is being subducted under another but that isn't the only place it is the dominant place or the most likely place to find mountains or volcanoes on the surface of the earth but that's not the only place that mountains or volcanoes can form and probably the biggest example of volcanic activity or the most popular one this might be a slightly American Amero centric point of view but the most often cited example of volcanic activity away from a plate boundary is Hawaii Hawaii so this right here these are the Hawaiian Islands this is the Big Island of Hawaii and it is it is experiencing active an active volcano lava is or magma was flowing from underneath the ground and that once it surfaces we call it lava and that lava is actively making the island is actively making the island bigger so where is that volcanic activity coming from and then how can we think about that volcanic activity or that kind of heat rising from below the surface of the earth to explain some of the geological features we see around Hawaii so what we think is happening and once again this is all theory right here is that Hawaii is sitting on top of a hot spot in particular the Big Island of Hawaii is sitting on top of the hot spot right now and this hot spot this hot spot there's different ways different theories on how it might emerge but we think that at the mantle at the mantle core boundary and I don't know in this diagram whether they intended this white area to be the core but let's just say that this is the outer core down here let's just say that this is the outer core outer core for the sake of for the sake of explaining things we they it's possible that kind of plumes of very hot material can kind of just based on kind of the fluid dynamics of what's happening at that mantle outer core boundary that plumes of really hot material can kind of rise up can kind of let me do this in a darker color can rise up from the outer core they would rise up from the outer core and then create hot it's underneath the moving lithospheric plates underneath the plates now it's not necessarily don't know for sure whether the hot spots are being created from by these mantle plumes these this material formed or heat it up at the outer core mantle boundary but what we do feel pretty confident about is that there is this hot spot here and it's independent of any of those convection patterns that we saw I shouldn't say independent it's obviously all related because we have all this fluidic motion going on in the mantle but it's it's it's separate on some degree from all of those convection patterns that we talked about that would actually cause the plates to move and to a large degree or the way we think about it right now this is stationary this hotspot is stationary relative to the plates and the reason why we feel pretty good about thinking that it's stationary relative to the plates is we see this notion right here if you look at the volcanic up if you look at the volcanic rock in kawaiii which is one of the older inhabited Hawaiian Islands the oldest rock that we've observed there is 5.5 million years old and it's all volcanic rock now the oldest rock we've observed on the Big Island is about seven hundred thousand years old we also know we also know that the Pacific plate you could look at this diagram right over here is moving in this general direction like we know it from we know it from GPS measurements it's moving exactly in the direction that the hawaiian islands are kind of distributed in so frankly the only good explanation for why we see this pattern well we see newer land here and then as we go further and further up the Hawaiian island chain we see older and older land and actually if we keep going if we keep going we have the leeward islands over here and as we as we keep measuring the rock on the leeward islands they get older and older as you go to the northwest and then if you even look at what's below the ocean this is the Big Island of Hawaii these are the main Hawaiian Islands these are the leeward islands but you see even beyond that submersed under the Pacific Ocean you continue to see a chain of islands so the explanation for what's happening here is that you have a stationary hotspot that is right now underneath the Big Island of Hawaii and I'll just want to be clear the Big Island is called the Island of Hawaii it is one of the islands in the state of Hawaii so I don't want to cause you confusion I'll just call it the Big Island from now from from here on out so the hotspot is right under the Big Island but if you were to rewind five million years ago if you were to rewind five million years ago the entire Pacific plate the entire Pacific plate was probably on the order you know about 150 200 miles however far kawaii is from the Big Island it was probably shifted that much to the southeast if you go back five million years ago so five million years ago when all of this was shifted down and to the right then kawaii kawaii was on top of the hotspot and so this is how each of these islands are formed if you rewind a ton of years then maybe this area over here on the Pacific plate was over the hotspot island an island formed there then the Pacific plate kept moving to the northwest it kept moving to the northwest and new islands new volcanoes kept forming those volcanoes would release lava that would keep piling up keep piling up heat piling up eventually go above the surface of the water and form this whole chain of islands and as a whole Pacific plate kept moving to the northwest it kept forming new islands now the one question you might ask is well how come the Big Island is bigger is it has the plate kind of paused over there is it spending more time over the hotspot so that more lava can kind of a form there to form this to form this essentially it's a it's an underwater mountain that's now also above the water and actually if you go from the base of the Pacific Ocean to the top of the Big Island of Hawaii it's actually 50% higher than Mount ever so you could really just view it as a big mountain but the question is this looks so much bigger than Kauai and they keep getting smaller as you keep going to the northwest is somehow the Pacific plate slowing is it is it spending more time here and the answer is it's probably not slowing what's happening is at one time Hawaii was also probably a relatively large island if you rewind five maybe five five million years ago kawaii also might have been about that big but over five million years is just experienced a ton of erosion remember once it moved over the hot spot new land wasn't being created it's in the middle of the Pacific Ocean it's experiencing weather five million years is a long period of time and so it just got eroded over that time so the older the island is the more erode it's going to be and the smaller it's going to be so if you go to these if you go to these underwater mountains up here that don't even surface above the ocean at one time they might have surfaced but over due to the ocean and weather and whatnot they've just been eroded over time to become smaller and smaller kind of remnants of volcanoes so anyway I thought you would find that entertaining of how the Hawaiian Islands actually got formed and how we can actually have these hotspots and these these this volcanic activity and actually even earthquake activity outside of actually a plate boundaries actually while we're looking at this diagram we talked about we talked about the trenches that plate boundaries you can actually see it here went because this shows the depth and the really dark dark dark dark blue is really dark deep parts of the ocean so this right here is the Mariana Trench and you can see over here the Pacific plate just getting abducted or she's not abducted getting subducted into other plates underneath and forms these trenches here anyway hopefully you found that entertaining