Geotweeps Discuss...

Informative and/or fun conversations between the geological community on Twitter, archived for posterity.

Oct 16

What’s being erupted at El Hierro

The eruption at El Hierro in the Canary Islands is taking place under the sea, but pictures from the scene are starting to show products of the eruption floating to the surface. But what are they? Read on for a crash cause in volcanic rocks that can float.

The undersea eruption has manifested at the surface in the form of a plume of dirty brown water. 

Of particular interest to watching geobloggers are these dark specks floating within the plume.
Take a look at the steaming scoria (like reticulite if its floating, right?) from the eruption off of El Hierro: http://t.co/tuCvCg0t
eruptionsblog
October 15, 2011
@eruptionsblog Reticulite would actually sink - the bubbles are all connected thus no way to hold the gasses in and water out.
rschott
October 15, 2011
@rschott You’re completely right - but I’m still perplexed about floating, dark pumice. Seen anything like it?
eruptionsblog
October 15, 2011
@eruptionsblog Haven’t collected anything like it (probably not very robust) but I’d imagine it’s just gassy scoria/mafic pumice.
rschott
October 15, 2011
@eruptionsblog … or, to put it another way, a black sand beach waiting to be pulverized by the waves.
rschott
October 15, 2011
@rschott If the pumice started out pretty dark (gray), being wet might make it look black.
Tuff_Cookie
October 15, 2011
@Tuff_Cookie I’d imagine this stuff has the texture of pumice or very frothy scoria, but it’s almost certainly mafic in composition.
rschott
October 15, 2011
@eruptionsblog @rschott so, given it’s formed underwater, would the bubbles be initially caused by steam? or volcanic gases?
Suw
October 15, 2011
@Suw Yes and yes. The volcanic gas is probably mostly water vapor/steam, though undoubtedly there’s some sulfur-bearing gas in there too.
rschott
October 15, 2011
@rschott @eruptionsblog I seem to remember seeing some on Stromboli…still, it was pretty pale. Nothing like the El Hierro photo.
Tuff_Cookie
October 15, 2011
@rschott @eruptionsblog Probably what I saw was a bit of this “golden pumice”: http://t.co/GdnhQECG
Tuff_Cookie
October 15, 2011
Experimental Crystallization of a High-K Arc Basalt: the Golden Pumice, Stromboli Volcano (Italy)
The near-liquidus crystallization of a high-K basalt (PST-9 golden pumice, 49·4 wt % SiO2, 1·85 wt % K2O, 7·96 wt % MgO) from the present-day activity of Stromboli (Aeolian Islands, Italy) has been experimentally investigated between 1050 and 1175°C, at pressures from 50 to 400 MPa, for melt H2O concentrations between 1·2 and 5·5 wt % and ΔNNO ranging from −0·07 to +2·32.
@Tuff_Cookie @rschott @suw So, the stuff at El Hierro is dark, steaming and floating. Likely mafic composition - which usually makes scoria.
eruptionsblog
October 15, 2011
@Tuff_Cookie @rschott @suw Might it actually be clots of dark ash?
eruptionsblog
October 15, 2011
@eruptionsblog @rschott I’d be interested to see how long it floats - feel like ash or scoria would eventually get waterlogged and sink.
Tuff_Cookie
October 15, 2011
@eruptionsblog @Tuff_Cookie @Suw I’m guessing mafic composition based on El Hierro’s previous erupted products & the evident low viscosity.
rschott
October 15, 2011
@eruptionsblog @rschott is there a difference between that & the glassy stuff at top of most basalt lava flows?
EarthlikePlanet
October 15, 2011
@eruptionsblog @rschott e.g., you looking for something really puffed up, or what?
EarthlikePlanet
October 15, 2011
@EarthlikePlanet @rschott You need lots of isolated air bubbles to get the density less than water.
eruptionsblog
October 15, 2011
@rschott @eruptionsblog @Tuff_Cookie Is this what the El Hierro stuff looks like? I got this in Alaska: http://t.co/uDyR0PVw
aboutgeology
October 15, 2011
Scoria, Alaska
Photo of Alaskan scoria.
@aboutgeology @rschott @tuff_cookie We might have a winner!
eruptionsblog
October 15, 2011
@eruptionsblog is that how you’re defining pumice from scoria, by density? Seems reasonable I suppose. @rschott
EarthlikePlanet
October 16, 2011
@EarthlikePlanet Although one could use it as a purely textural term, I think pumice generally implies intermediate to felsic compositions.
rschott
October 16, 2011
@EarthlikePlanet I use scoria for anything mafic and highly vesicular.
rschott
October 16, 2011
@rschott I would agree, it is mainly amount of volatile content and viscosity that allows them to puff up. But unusual things happen.
EarthlikePlanet
October 16, 2011
@rschott @EarthlikePlanet We used pumice for >50% void in felsic/interm, scoria for >50% void in mafic; vesicular for <50% in anything.
lockwooddewitt
October 16, 2011
@lockwooddewitt @rschott I think that’s a decent classification but then by definition there’s no such thing as mafic pumice.
EarthlikePlanet
October 16, 2011
@EarthlikePlanet I don’t use the term “mafic pumice” myself, but I understand what people mean if they use it. ‘Nuf said.
rschott
October 16, 2011
@Tuff_Cookie @eruptionsblog @rschott a guy from CSIC has just said that are pillow-lava fragments and so the magma ought to be below 200m.
Lumifg
October 16, 2011


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