<p>Felsic magmas contain much more silica (SiO2) than mafic magmas (almost by definition). The excess silica chains cause the magma to be much more viscous and therefore more prone to explosive eruptions (they trap gas and require high pressures to flow). This is why felsic magmas produce crazy explosive pyroclastic flows (forming ignimbrite) and very mafic magmas (like in Hawaii) just flow nicely downhill.</p>

<p>Btw, water decreases the viscosity of magmas, but the amount depends on composition as well as temperature. There is a nice transition between felsic magmas and mafic magmas showing that decrease in viscosity. Check out the source below:</p>

<p><a href="https://link.springer.com/article/10.1007%2Fs00445-008-0217-y" rel="nofollow noreferrer">Whittington et al (2009): "The viscosity of hydrous dacitic liquids: implications for the rheology of evolving silicic magmas"</a></p>

CC BY-SA 3.0
2017-04-12T16:33:00.863Z
2017-04-12T16:40:36.503Z
2017-04-12T16:40:36.503Z
Antonio
<p>Explosive volcanism is ALWAYS associated felsic magmatism, only because of it's higher water content, whereas mafic magmas are much "drier".</p>

CC BY-SA 3.0
2017-04-12T04:54:12.507Z
2017-04-12T04:54:12.507Z
Knob Scratcher
<p>Why is ignimbrite associated with only more felsic magmas?</p>

<magmatism>
Why is ignimbrite associated with felsic magmas?
user7885
# Why is ignimbrite associated with felsic magmas?

(Asked by: username_0 on 2017-04-11)

Why is ignimbrite associated with only more felsic magmas?

**Tags:** magmatism


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## 2 answers

### Answer by username_1 on 2017-04-12. Score: 4

Felsic magmas contain much more silica (SiO2) than mafic magmas (almost by definition). The excess silica chains cause the magma to be much more viscous and therefore more prone to explosive eruptions (they trap gas and require high pressures to flow). This is why felsic magmas produce crazy explosive pyroclastic flows (forming ignimbrite) and very mafic magmas (like in Hawaii) just flow nicely downhill.

Btw, water decreases the viscosity of magmas, but the amount depends on composition as well as temperature. There is a nice transition between felsic magmas and mafic magmas showing that decrease in viscosity. Check out the source below:

[Whittington et al (2009): "The viscosity of hydrous dacitic liquids: implications for the rheology of evolving silicic magmas"](https://link.springer.com/article/10.1007%2Fs00445-008-0217-y)


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### Answer by username_2 on 2017-04-12. Score: 0

Explosive volcanism is ALWAYS associated felsic magmatism, only because of it's higher water content, whereas mafic magmas are much "drier".


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