Sunday, March 27, 2011

Re: [Geology2] Nyiragongo Crater by The Big Picture



If I can offer a thought, the outer edges will cool at a greater rate than the core of the flow, which would make it denser and slower.  After a period of distance, that vent would evolve into a circle because all the edges would have been slowed down. 

Does that make sense?

Rick

Tiny iPhone keypad + my fat thumbs = typos.  Sorry. 

On Mar 27, 2011, at 10:28 AM, Lin Kerns <linkerns@gmail.com> wrote:

 

Hi Bre,

I thought your question was an excellent one; in fact, I was just about bursting at the seams in order to find an answer. What I found was that the circular vent, the caldera, is a general form for most volcanoes, except for the shield volcanoes--like those in Hawaii. The shields are more unpredictable in their formation of the typical round caldera due to their particular type of eruption.

Therefore, I will focus upon the  factors present for the formation of the typical caldera:

Magma moves upward at a speed that is dependent upon the combination of the viscosity of material (dacite, rhyolite, basalt, etc.) with the amount of gases present. Magma is thrust upward through the points of crustal deformation much like a projectile and the faster it moves, the more it behaves like any force moving through its surroundings. Think of an arrow shot from a bow; even though you cannot see it, the arrow will displace air in a conical  manner due to the power of its thrust from the bow. Magma moving through the earth behaves in a like manner. It is what happens next that is exciting; the emergence of the magma and the formation of the caldera. And for that, I turn to a video I found that shows the exact process:

http://pubs.usgs.gov/of/2010/1173/

There is a paper published that focuses upon the properties of caldera formation HERE
I'm sure if you look around through various sources, you can find a copy of that paper without having to shell out the $41. for it. JSTOR is a good place to look, but if you can, search WORLDCAT and some library will have a copy of it. You can then request an inter-library loan.

I hope my crude manner of explaining the physics of caldera formation helps.

Lin

On Sun, Mar 27, 2011 at 9:33 AM, Lin Kerns <linkerns@gmail.com> wrote:
Looking for an answer for you, Bre.... I'll be back with one...

Lin

On Sat, Mar 26, 2011 at 6:28 PM, <LadyTozi@aol.com> wrote:
 

Okay, I'm late in reading my e-mails.  Spectacular photographs.  But I do have a question, it seems that in all of the photographs I have seen of central volcanic vents of various volcanoes Nyiragongo, Alta Erta, Shasta, Rainier, etc. the main vent is circular.  Why?
 
Bre
 
In a message dated 3/1/2011 11:00:26 P.M. Central Daylight Time, linkerns@gmail.com writes:
 
 




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--
Got Penguins? 

Penguin News Today
The Science of Penguins
The Gentoos are back! Come see them on live cam at:
Gentoo Penguins of Gars O'Higgins Station, Antarctica

 



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