Magma Viscosity, Volatile Content, Partial Melting, & Mixing- Igneous Petrology #6 | GEO GIRL
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- čas přidán 23. 07. 2024
- What controls how explosive a volcanic eruption is? This video covers the difference between felsic and mafic magmas in terms of their silicate content and structure and the crystallization processes and rocks that result from each, how volatiles like water and CO2 affect magma viscosity, and how the viscosity of magma affects the explosivity of volcanic eruptions, the factors that control magma viscosity and density, how density affects magma ascent and eruptions, how melts are formed, in particular how partial melting works, how fractional crystallization works, and lastly, what magma assimilation and magmatic mixing means. Viscosity of magma determines how explosive its eruption at Earth's surface will be. Volatiles content and temperature of magma controls the viscosity of the magma. Explosive eruptions occur when volatiles in viscous magma exsolve as the magma rises to Earth's surface and the pressure changes. This extreme change in pressure when the magma reaches the surface leads to a huge push to get the magma to explode out of a volcano, where it then becomes lava then solidfies into igneous rock. Felsic magmas are typically more viscous than mafic ones, thus mafic eruptions are more like oozing flood than explosions, which leads to flood basalt formation. For the second half of this video, I go through magma differentiation by partial melting and magma mixing which can occur in magma chambers below Earth's surface. Partial melting lead to eurpted lavas that are always more felsic than their source because felsic material melts at lower temperatures than mafic material. This melting/crystalization trend follows the Bowen's Reaction Series, which I talk more about here: • Igneous Rocks and Bowe... . Hope you enjoy this video and learn as much as I did in making it! ;D
References: Essentials of Igneous Petrology by Ronald and Carol Frost: amzn.to/37Zs9AL
Earth Materials by Cornelis Klein and Anthony Philpotts: amzn.to/3z5sCxe
GEO GIRL Website: www.geogirlscience.com/ (visit my website to see all my courses, shop merch, learn more about me, and donate to support the channel if you'd like!)
0:00 Felsic vs mafic magmas
3:43 How volatiles affect volcanic explosivity
7:21 How volatiles affect viscosity and vice versa
9:04 what happens when you blow bubbles in viscous materials?
10:10 What controls viscosity?
11:18 How magma density affects eruptions
13:34 Partial melting of magmas
18:59 Fractional crystallization of magmas
21:40 Magma assimilation & mixing
23:13 Upcoming videos!
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Ok I'm certain I will forget 95% of the content in the next day or so, but while I was listening to it, dang that was awesome. Strong work.
Thanks! haha, don't worry I forget half the things I talk about on my channel, I literally have to watch my own videos sometimes 🤣
Great video as per usual! I really enjoyed the "blowing bubbles in water vs honey" analogy. This device really gets at the physical processes acting in the silicic vs mafic magmas in regards to volatile dissolution and the explosivity of the eruption. I wish you made this video years ago, that would've helped me understand this process way faster 😂. If you teach at all I would recommend using this analogy.
Thanks! I am so glad you liked the analogy haha, I loved it as well. :D I didn't actually learn it that way until way later, I too wish I was taught it like that!
I watched this last night but I forgot to comment. I think I’ll watch it again.
I ❤️ GEO GIRL!
Yay! So glad you liked it, thanks for the comment Joe :D
Great video!!! Thank you for breaking down all these useful processes!
The way you break down the information it'sreally impressive.
We need more people like you.
I really focus with you, more then when I'm at college. In college I feel like some of the teachers are just waiting for their check , with you it's just geology.
As a student, thank you so much.🌹
From student to student, I totally understand and I greatly appreciate your comment! I am still a student myself (as well as a teaching assistant) and I agree that many professors teach in a way that is not engaging or interesting. My goal was to try to make things more exciting when I teach, so your feedback is very nice to hear. Thank YOU! I will forever continue to try and find new and exciting ways to teach. ;)
@@GEOGIRL to be honest when I see your videos.
I get really excited to learn more and more.
And I wonder what the hell I'm doing with my life 😂😂😂.
and I really wish that you tell us more about you and how you got yourself in to geology.
And I really wish you all the joy in the world because you bring happiness to me everytime I watch you.
@@geologist803 Haha, I can't believe you asked to know more about how I got into geoloy, because as it turns out, I have a video on that exact topic: czcams.com/video/61pUuO8C8hU/video.html :)
Thanks so much for your support and encouragement, it really does mean so much to me! I am so glad my videos bring you happiness :)
I can't blow bubbles into my honey, but then the honey in my cupboard is partially crystalized with phenocrysts of sugar in a very very viscous honey matrix, and I'm in a cold place so the honey is viscous because it is cool. Maybe if I were in El Paso with hot fresh honey I could blow a bubble or two. Who knows :) Loved your video.
Ahhh! Wow good hypothesis Barbara, it's like you are a geologist yourself! ;)
This is the best I have heard it explained
Currently in petrology and this is good review before exams. New subscriber!
So glad to hear that, best of luck! ;D
Thanks for this video❤
my girl you are literally saving my ass throughout college. God bless u
Ok geo-noob here - but would composition be more of a source or time dependent process? What I mean is, is a lava more likely to be felsic due to it's chamber taking longer to reach the surface thus able to fractionate it's minerals to greater extent or because it simply was more felsic to begin with/more felsic host rock?
Also, does the addition of volatiles affect the temperatures/pressures at which minerals will fractionate? If so, how might this factor into the surface composition?
Well it is both source and time dependent (but time would affect grain size more than composition). The composition is more so temperature-dependent. If subsurface rocks are heated to ~600 deg C but no more, only felsic material would ever melt from those solids and eventually it would rise to the surface where it cools to form felsic rocks. The residual subsurface solid will be left more mafic and the results rock we find at the surface is more felsic than its source was. This case has little to do with the source composition and the duration of time that it was heated, and more to do with the temperature that it was allowed to reach. It takes very high temperatures to melt mafic material and even higher to melt ultramafic material, making these more rare at Earth's surface.
However, you do make a good point, we also have to take into account the source composition, because what if the source was completely felsic and we interpret the resulting rock as being a partial melt, when really it was a complete melt of a felsic source magma. This is where we use more specific chemistry and isotopic compositions of igneous rocks to understand which scenario it really was (I will talk about this in the upcoming chem of ig rocks video :) But regardless, we can say with absolute certainty that "every partial melt is more felsic than its source" because we are already defining these as partial melts and we have experimentally determined this to be true in every source composition scenario.
Lastly, yes, volatiles (namely water) will lower the melting and crystallization temperatures of minerals, but to my knowledge this occurs equally to all minerals such that the order in which they crystallize based on temp stays the same and the only thing changing is the actual temps at which they begin to melt/crystallize. But since the order (bowens reaction series order) stays the same, nothing compositionally is really affected.
Hope this helps, great questions btw! Thanks for asking :D
On the Andean volcanic range there is a gap, from the south of Ecuador to the south of Peru, about 2000 km without volcanoes. I have read that it is due to the angle (small angle) with which the Nazca plate goes under the South American plate. Could you explain how it happens, why that angle matters. Thanks.
Wow! How cool. I looked at some volcanic activity maps and it seems there are still volcanos along this stretch, but it may be that they are just less abundant or less active in this region. I am not exactly sure why the angle would cause this, but my best guess it that it affects the angle at which the slab is subducting. Subduction is often steep, in which the slab goes deep into the mantle and causes volcanism/mountain building close to the plate margin. But sometimes subduction is shallower causing volcanism/mountain building further inland from the plate margin. I am not sure if the angle is steeper or shallower along this stretch but my guess is that is causing a difference in the volcanic activity. The other thing the angle could cause is more transform movement than subduction, or a slower rate of subduction which would cause volcanism less often than faster subduction rates.
But I guess the short answer is the angle could be causing multiple affects that would lessen the volcanic activity in this region. I am not sure which factors are at play for this scenario, but I hope this helps point you in the right direction. :)
If you figure it out, let me know! I am curious now haha.
*Thank you for making such educational videos. Thanks from India.*
Of course! I am so glad you find them helpful! :) If you ever want to suggest a specific topic that you are struggling with, I am all ears ;)
I did not try to blow bubbles into honey after watching your video, because you taught me so well that it would produce a violent eruption due to its viscosity. I did however rejoice in adding Norman L. Bowen to my list of favorite, early 20th century geologists; right there in the ranks of Walter Elsasser, Preston Cloud, Walter Alvarez, Alfred Wegener & most of all Clair Patterson.
Also, I don't know if it was this video or not, but I learned from you that water reduces the viscosity, and carbon dioxide increases the viscosity, of magma. And I learned how igneous differentiation alters the its composition.
p.s. sorry for calling your channel a pyramid scheme before... I was only kidding, but on the internet sometimes that isn't apparent.
Haha, I don't even remember the pyramid scheme comment lol but I am very glad you learned so much from this and other videos about magma! :D I love your list of geologists, those are such great options, my fav is also Clair Patterson! :)
Dear Geo Girl, i will be going to rodrigues island soon, i will be admiring-analysing the rock formations there thanks to you, your absolute beauty, your courses and your singing.
Oh yay! That's so exciting! Enjoy :D
Thanks for the video. It was a very good explanation. good luck with your efforts
Thank you! :)
Could you please tell in detail about igneous rock textures in your upcoming lectures . It will be very helpful for me 🙏
Actually, I already have videos over igneous rock textures: czcams.com/video/UJSz2Z7IEXY/video.html, and lava cooling structures: czcams.com/video/JkdU9aQykHQ/video.html. I go over concepts like why basalts are coarser grained than rhyolites in the textures video! :D Hope this helps ;)
Thank you ma'am.. I'm a Geology student . This video helps me a lot .., thanks again ❤️
So glad you found this video helpful! Thanks for the comment ;)
what a great video, i took about 1 hour of this 24 min video bcz of reviving again and again to fulfil my concepts, I got too much & hope the next video will be of magma & lava solidifying textures and the complete phenomenon occurs behind of finer rhyolitic and coarser basaltic Why? like such tetrahedra bonds examples & Also, well explained everything but i need to ask about the concept of volcanic arc formation like how are they parallel to the subduction of plates and lastly, is there the concept of fractional distillation occurs in ophiolites too or not ? hoping having a kind response.Thankyou
Actually, I already have videos over igneous rock textures: czcams.com/video/UJSz2Z7IEXY/video.html, and lava cooling structures: czcams.com/video/JkdU9aQykHQ/video.html. I go over why basalts are coarser grained than rhyolites in the textures video! :D
Also, regarding subduction zone volcanism, the volcanic arcs are parallel because the subducting plate (wherever it is subducting under) brings down water with it inducing melting of the mantle, which causes the volcanic activity.
Lastly, technically no, ophiolites do not undergo fractional crystallization processes because ophiolites (as they are defined) are already solidified and at the surface. But since they are derived from upper mantle material, I think I would say yes, because the upper mantle does undergo fractional/partial melting and subsequent fractional crystallization processes.
Hope this helps! ;)
Tanks...
Thank you for doing these (:
Of course! Thanks for support :D
nice video
You are cute ...😊