Talk:Island arc

Black sand beaches
Not happy about the phrase "Weathering and erosion of these volcanic rocks produce black-green beaches composed of olivine sand eroded from the volcanic cones." While some calc-alkaline volcanics are oliving-phyric, it's not particularly common. Black-sand beaches are more often composed of ilmenite and magnetite, with olivine a relatively minor component. A Karley 12:45, 10 August 2006 (UTC)

Merging Island arc into Volcanic arc
After editing both of these articles today, it seems clear to me that this one should be merged into the other. All island arcs are volcanic arcs, so this article is just a subset of the other. There is already major overlap in content in the two articles, so this was an easy decision to make. Better to have one nicer, more comprehensive article than just leave these two as they are now. --Seattle Skier (talk) 01:16, 13 April 2007 (UTC)

I agree with you that island arc should be merged into Volcanic arc as a sub-section accompanied with continential volcanic arc.Tranletuhan (talk) 09:37, 14 April 2009 (UTC)

Yes, I agree as well. Geologist (talk) 20:49, 23 October 2009 (UTC)

Why are volcanic arcs arced?
'This is a consequence of the geometry of the spherical plate crumpling along a line on a spherical surface.' This sentence appears to have no content: it states that the arcuate shape is a consequence of two plates meeting. (Also 'curve' might be better than 'line'.)

The thought behind the above quote could be that a flat plane intersects a sphere in an arc. This idea is a nice one, but doesn't fit well with observation. On the spur of the the moment, I can come up with perhaps better hypotheses. Could someone provide several references to a current theory as to why arcs are arced, and what the varying geometry of arcs consequently tells geologists?

If current plate tectonics provides no explanation, then some big change or addition to current tectonic theory is awaiting: one should perhaps not ignore the arcs as trivial and let the reader think that current plate tectonic theory explains them well.

In short, plate tectonics explains the 'islands' and 'volcanic', but not the 'arcs'. Perhaps this should be made clear. Geologist (talk) 20:49, 23 October 2009 (UTC)

I have just realised that no-one has answered the question. Volcanic arcs form because of the geometry associated with the sides and the centre. At the sides there is a restraining force which also generates friction as the plates oppose each other in a similar manner to a transform fault except that a position on one side of the linear fracture will move away from a reference point on the other side, whereas in a transform system they remain in the same relative position. Like a river or a glacier the greatest motion is in the centre and this can move forward faster than the friction at the sides allows. A good example is the South Sandwich Island Arc, which is pushing eastwards relative to the floor of the South Atlantic. As a matter of interest to non-geologists, a map of the arc indicates which plate is over-riding and which is being subducted. The arc, like a bow under tension, points at the subducting plate like this: over-riding plate -->) || trench and subducting plate.The Geologist (talk) 16:38, 10 April 2012 (UTC)

Japan
I'm under the impression that Japan is actually a piece of the mainland pulled off as the ongoing subduction stretches the riding plate, and not really an island arc per se. —Preceding unsigned comment added by 71.135.102.61 (talk) 04:54, 24 March 2010 (UTC)

Gravitational Pull?
The section on oceanic trenches asserts that trenches are the result of a "gravitational pull" effect: 'This trench is created by the gravitational pull of the relatively dense subducting plate pulling the leading edge of the plate downward.' I doubt, however, that this actually relates to the force of gravity. I would suppose that it relates more to the rigidity of the lithosphere, with the subducted edge pulling down the attached ocean floor nearby due to tension. Will someone more knowledgeable than I confirm this, or add references? JackS333 (talk) 20:33, 9 May 2010 (UTC)

Hotspots
I have added a "{missing}" tag and included the info I think is missing. Not all island arcs or chains are related to subduction, and the current article does not explain the existence of intratectonic chains such as the Hawaiian Islands. 77.165.250.227 (talk) 14:04, 22 May 2015 (UTC)
 * Hotspot volcanic chains are formed completely differently. Volcanic arcs result from specific mechanisms of formation, and are their own separate feature. — Gorthian (talk) 20:40, 6 June 2016 (UTC)

Driver of melting beneath arcs
The article says ''It is now believed that water acts as the primary agent that drives partial melting beneath arcs. It has been shown that the amount of water present in the down-going slab is related to the melting temperature of the mantle., which sounds fine but then goes on to say The greater the amount of water present, the more the melting temperature of the mantle is reduced''. This is confusing. If water reduces melting then how can it be the primary driver? — Preceding unsigned comment added by 85.211.226.224 (talk) 15:34, 3 February 2019 (UTC)

Hawaii
Isn't Hawaii a Volcanic Arc? The Hawaiian Arc is very large, and it extends, completely engulfing the Midway Arc. Even the wikipedia page for Hawaii shows that Midway Islands are, in fact, part of the Hawaiian arc. ConlangingMango (talk) 11:51, 28 July 2020 (UTC)