VOLCANO MADNESS: Re: [Geology2] Nyiragongo Crater by The Big Picture

Sunday, March 27, 2011

Re: [Geology2] Nyiragongo Crater by The Big Picture

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:

28 Great Images of Nyiragongo--Crater Click Here

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