Geology 101 with Willsey, Episode #3: Divergent Plate Boundaries
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- เผยแพร่เมื่อ 26 มิ.ย. 2024
- New to geology, want to learn some basic concepts, or just need a geology refresher? Join geology professor Shawn Willsey for this new series as he presents the same lectures as his GEOL 101 (Physical Geology) course. These videos are for everyone.
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Animation: • Divergence
00:00 intro
1:36 divergent boundary characteristics
8:40 animation
10:40 Google Earth examples
17:44 quiz question - วิทยาศาสตร์และเทคโนโลยี
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Thanks Shawn. 🙂👍
Really am enjoying this. I took geology in the mid 1960s when they were just beginning to teach tectonics. There was still some doubters around. There's was no Google earth or internet so this is really great.
I still have a few old geology textbooks around that treat plate tectonics as a new and controversial theory .
Shawn thank you for all the geology you are putting out there. I am overjoyed for this series you are doing on beginning geology. Again thank you.
Wow, another great video Shawn! Thank you so much for this series! Can’t wait to learn more about convergent plate boundaries. These explanations are really helping cement my understanding of these concepts! One question that comes to mind is to what extent rifting pushes the continental crust versus subduction in other places pulling the plate boundaries apart? This came to mind when you were discussing the decreased pressure at the surface of the crust promoting magma formation in the aesthenosphere. Maybe pushing and pulling are the wrong concepts to apply here, but those were the words that came to mind. Thanks again!
Slab pull is more dominant than ridge push. You can see evidence in speed and number of quakes along subduction zones.
@@shawnwillsey Thanks Shawn, that makes sense to me and helps me better understand the process!
@@seanmccaul3034 To add to what Shawn said it should be noted that slab pull is a gravity dominated process as the subducted slabs sinking down into the Earth effectively drag the rest of the plate with them.
You can consider the ridge push to largely be a response to the pulling of slabs, though there are of course exceptions particularly major mid ocean ridges with hot spots of upwelling material which seem to have deeper origins i.e. the East Pacific Rise and Mid Atlantic Ridge. Nature loves exceptions, the rate of sea floor spreading between mid ocean ridges can vary by up to 2 orders of magnitude for example though again as Shawn said subduction generally is faster.
The seismic tomography stuff is adding fascinating details to the picture too for example it appears that subducted slabs under go remineralization as the sink deeper into the planet and get subjected to higher and higher pressures which forces out lighter incompatible elements/volatiles and then causes the slabs to sink even more. There is some evidence to suggest they sink all the way down to the core mantle boundary before they get remelted by the heat of Earth's core and contribute material to the upwelling plumes of material rising to Earths surface. In essence the slab itself is the Earth's downwelling convective element.
@@Dragrath1 Thanks for the additional information! That’s why I love this channel, always learning something new!
Thank you!! Great information and so clearly presented, as always! That little peninsula on the east coast of the US where you drew your line for the Mid-Atlantic Ridge is the Delmarva Peninsula, the southern part of which is in Virginia and my home area. ❤
I’m loving this 101 series!
Super. A good knowledge of the basics makes everything after more comprehensible.
I learned absolutely nothing, but I still loved the video. I want more geology on TH-cam and you are providing. Thanks and rock on!
Thx Prof. ✌🏻 really appreciate this series.
I've now watched all three of your Geology 101 videos and they are great!! Thank you for doing this....I've always been fascinated with geology, volcanology and pretty much all earth sciences but as a single Mum of 4 kids, school wasn't an option but now that my youngest is 18, it's time to go back!! I'm watching these videos hoping it will help me choose a direction in school!! Thank you for all your hard work and being a dedicated teacher!! Keep it up 😊
Awesome, thank you! I love your story.
I got the right answer! Only because Shawn explains things so well.
Shawn, thank you for making an incredible series! I am absolutely loving it and you’re a natural born teacher! Thank you so much for these videos. Can’t wait for the next one
You are so welcome! Thanks for watching.
Excellent, thank you.
Another fantastic episode… I learn and find great enjoyment in it … I love planet processes.. thank you shawn
Thank you for another great Geology video, Shawn. You make it easy to follow and the diagrams help me visualise the subject. I like that you are covering the different plate boundaries in different videos, that is giving me time to take it in and helping to get it into my brain. Brilliant.
Glad to help!
Wow I never studied geology at school. So interesting to learn something new through your fantastic videos. Thank you!
Yes, super interesting. Looking forward to episode 4.
Excellent Series. Thank you for your diligent efforts.
Thank you for another great video Shawn. I was in my mid twenties during the 1960s when the theory of plate tectonics was first generally accepted: we’ve certainly come a long way since then in our understanding of our world.
Interesting, I had figured out the center would be shallow but didn't realize there wouldn't be any others further out. Thanks for the class!
Wonderful, wonderful, wonderful to quote the late Mr. Welk.
Really appreciate these videos. Thank you so much.
Excellent! Thank you!
Thanks, Shawn. I’m finding this very interesting.
Thank you, Shawn!🙂
Would the Upper Rhine Graben be also considered a divergent boundary? From what I know, the plain is still experiencing subsidence, but is being supplied with new sediment at a rate high enough to not form a deeper valley.
Sooo looking forward to your 3rd lesson! Gracias!
I love this series. Is there a theory that takes an upwelling of magma into a tear that is thousands of miles long? Is there an initial start to the mid-atlantic ridge identified?
Another great episode, thanks!
Loving this. Thanks so much.
For every successful rift on land in the middle of a continent, there probably are several failed rifts that leave behind long, thin lakes such as Lake Baikal. Why rifts succeed or fail is an interesting question. The rift in East Africa seems to be succeeding but we can't be sure. Lake Tanganyika and Lake Malawi are signs of a rift in any case.
North America has many such failed rifts , including the New Madrid seismic zone .
Farther north from Michigan through Minnesota was another tremendous rift that simply filled with basalt and stopped , but brought massive amounts of iron ore , copper , and other metals along for the ride .
Meanwhile the Rio Grande Rift is slowly tearing apart the southwestern US and on into Mexico .
Nothing is forever .
@@kaboom4679 thanks!
Hi Shawn, I am so excited to have found your channel and now that you have these videos. I have a rough idea from school, a long time ago so enjoying having my knowledge enriched.
Thank you, great video!
Thank you Shawn. Very enjoyable presentation.
Glad you enjoyed it. Thanks for your support.
Asante sana mr shawn..
Masterclass. Now I need to try and get my head around decompression melting.
We can tackle that when we discuss igneous rocks.
Hey there, long week... But it's the weekend, hooray! Perfect time for a good geology lesson, so let's watch your Geology 101, episode 3. Thank you (again) for doing this, Shawn! (ps: pizza sent ;)
Thanks as always, Sandrine.
Very good once again
Again I think you have the asthenosphere and upper mantle inverted (or rather the asthenosphere is part of the lithosphere and upper mantle)
In terms of divergent plate boundaries it should be noted that continental rifts can get much more complicated often involving multiple competing rift centers before one eventually comes to dominate. A good example of such a well developed failed rift is the strait separating Greenland from North America ultimately the eventual split was to the east splitting Greenland from what is today Ireland and the Scottish coast of Britain. There is even another less developed failed rift or graben which forms the Irish Sea separating the two islands.
One curious divergent plate boundary which breaks the rules is Gakkel ridge the ultra slow spreading ridge of the Arctic ocean which does produce explosive activity. The type of magmas erupted here are somewhat unusual as it seems a good amount of the volcanoes here have melt sitting long enough to undergo crystal fractionalization turning into more siliceous and chemically evolved melts which in addition to more typical pillow basalts build up stratovolcanoes lava domes and calderas with clear evidence of recent pyroclastic eruptive activity and even some older evidence for an extreme VEI 8 super eruption dated to roughly 1.1 million years ago. By far the strangest ocean ridge mapped, I want to know why the eruptive activity is so explosives here my guess is that the magma is probably too cold for the water associated with the volcanism to be supercritical like occurs at typical deep sea ridges under the high pressures and temperatures. This would mean the water could flash to steam as the gas and liquid phase are still distinct despite the high pressures.
The most peculiar and or interesting divergent plate boundary might be the Basin and Range province and the associated Rio Grande rift Valley or if counted separately the rifting splitting away the Sierra Nevada Great Valley block away from North America. This seems likely to be a consequence of North America subducting a major mid ocean ridge and associated hot spot which has gradually torn away at the NA craton but it is a good example of how you can't readily separate divergent and convergent plate boundary behavior as they are coupled(Earth isn't getting any bigger after all).
Another interesting divergent plate boundaries not covered are the Baikal rift zone and the associated pull away basin which makes the Korean peninsula as the Amur plate separates away from Eurasia. This appears to potentially be related to the flat slab subduction with melts chemically very similar to the basalts seen during the rifting of supercontinents.
And as a last example to note Antarctica provides a curious example of an active rifting continent buried underneath ice which currently is acting as a lid on activity.
Hell yeah les go!
Hi Shawn, thank you for doing this series, I've been really enjoying it!
One question I have that maybe I'm missing the concept for is why in the Mid-Atlantic rift, there is volcanic activity and new crust staying at a higher topographical point but as shown with the divirgent plate boundaries of East Africa and The Red Sea, we don't see that and the place of divirgence is at the lowest topographical point?
Thank you! I need to stick with my first choice when it’s multiple choices! 😂
Thank you
Well this is great I have learned a lot from Nick’s 101 lectures
I don’t know if you have time to answer questions about the quiz; I understand how busy you are! (Quiz answer spoiler alert, viewers!). ❓I compared the ocean basin earthquakes plots to the Iceland erupting volcano situation and remembered that in Iceland there were small, deep earthquakes farther away but still possibly secondarily triggered by the rift area activity. On the map, off to the sides, roughly east and west of the rift zone. But the Atlantic Ocean basin rift does not cause earthquakes off to the sides in your quiz answer. ❓Could the reason for the difference between the Iceland earthquake example and the quiz’s ocean basin example be the smaller scale of the Iceland example (fewer kilometers involved)❓Approximately how wide is the Atlantic rift where earthquakes happen?
I’m looking forward to the convergent plates episode. Thank you!
Thanks professor 🙏
Rio Grande rift by the Jemes Mountain in the US state of New Mexico. I always wondered if if goes all the way up to Salt Lake.
Professor is Salt Lake a sag pond? 🤔
What I'm curious about is the African Rift Zone in context to its surroundings. It seems that the Red Sea, Dead Sea, and even Madagascar have to be related, if in only to the degree that with all of the planetary rifting going on, that portion of the globe seems to be particularly actively rifting. Inquiring minds go hmmm.
I have a question: At one point you said that the plates are being "pulled" apart at the divergent boundaries. Wouldn't "pushed" be a better description? Doesn't the upwelling magma force the plates apart? If they are "pulled" apart, what provides the attractive force?
Thanks!
Much appreciated.
TY
i would think a would be the correct choice but the amount of quakes would lessen the further away the new material would get from the birth place till the point it meets the continental crust and there the Quakes would increase again
I did learn something new today lol I was wrong on the earthquakes and did not choose e. Now I know different.
QUESTION: In a different lesson, you told us that the crust below oceans is basalt, and on continents it is granite. In the case of diverging plates, dopes the lava that comes up to fill the gap end up as basalt or granite depening on whether under strong water pressure or whether neat ground level? Or doe the gap between two contine ts that spread apart remain lava in nature forever ?
Since Québec used to be attached to France a few years ago (hence our common language 🙂), and you had mentioned the floor of the atlantic was basalt, but as the 2 continents drifted apart, wouldn't that imply that lava actually filled the gap between North America and Europe?
It has nothing to d with pressure. Basalt is a low silica product and granite is a high silica rock.
Hi Shawn,
Per Google Earth, the South Gorda spreading ridge not only borders the Mendocino Fracture Zone (MFC,) it’s 4,000’ higher than the adjacent San Andreas-Pacific plate opposite the MFC. The 4,000’ MFC escarpment is abrupt, dramatic and structurally consistent along its length from the triple junction @125W Longitude to @129W Longitude where the Gorda-Pacific plate appears to have spilled its magma over the escarpment onto the San Andreas-Pacific plate floor; at this location, the MFC escarpment is still @4,000’ in relief and from there onward, the escarpment is no longer abrupt nor consistent.
Why the inconsistencies between 129W and 125W? Why no magma spillage over the escarpment West of 129W? The escarpment appears to be San Andreas-Pacific in origin and behaves as a natural dam impounding the fresh magma at the South Gorda spreading ridge. Any thoughts or observations?
Another great lesson! Is the basin and range a divergent plate boundary?
It’s not a true boundary but an area of diffuse extension. It could one day become a plate boundary.
I'm interested in the mechanisms that cause the decompression melting.
Temperature and pressure both increase as you go deeper underground, however, at most depths the pressure is high enough that it prevents the rocks from melting despite the rocks being very hot.
So decompression melting occurs when the pressure above already hot rocks decreases. The crust is thins out at divergent plate boundaries, thus the pressure above hot rocks decreases and those rocks are able to melt.
It's similar to how it takes less heat to boild water at a higher altitude because the air pressure is lower.
I read recently that the Indian continent is splitting. Would that be a rift similar to the Rift Valley in Africa?
❤❤❤
I live in metric area and thank you.
I mean... That's the vast majority of the world lol
@@austinobambino1360 to quickly convert feet to meters, divide by 3 and round down. e.g. 12000 feet is a bit less than 4000 meters (more precisely 3658). If you're going to be hanging around with those stick-in-the-mud Yanks, you need to develop a few tricks to convert units.
❓️Why are there such elevated ridges outside of the East African and Red Sea divergences?
I failed that quiz spectacularly.
I completed a Geology minor and got that wrong lmao
I over-thunk it; there _are_ occasional earthquakes that occur away from the plate boundary itself, but Shawn never said whether it was a rift or a spreading ridge. My feeble brain went straight to a rift and so I was like doing B or whatever. At a spreading ridge underwater the quakes are 100% along the boundary itself.
👍
How can you make a cut like that in google earth?
I thought the rift zone in Africa was North/South, yet you said East to West. Did I misunderstand?
A!
❤✌️👍
I so did not get the quiz.
Shawn. I don't understand the silence regarding my previous questions?
Ignorant.
SALUDOS EKUATORIALES ANDINOS DESDE PUENGASI KITU....LA LLAKTA DE ATAHUALPA...
Thanks!
Thank you kindly.