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My understanding is that the Hawaiian islands were produced as the Pacific plate moved over a stationary hot spot, which sent magma burning up through the plate as it passed over, forming a trail of volcanic islands on top.

But why dots instead of a line? In other words, why did that process produce islands instead of a continuous piece of land? Does the rising magma start and stop periodically?

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    $\begingroup$ This is a comment rather than an answer because answers should have references. The Earth's crust is a bit tough, but once magma has found a path through it, that pathway remains weak for a good amount of time, even between periods of eruptions. The same applies to the upper mantle. (It is erroneous to think of the Earth's mantle as being molten. It is mostly solid rock.) So once the elastoplastic material that forms the hot spot proper finds a way through the upper mantle, that will remain the preferred pathway for a very good amount of time. $\endgroup$ – David Hammen May 5 at 2:24
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    $\begingroup$ Whether the hot spot moves or is stationary (with respect to what?) remains a bit of an enigma. What is known is that there has been and still exists relative motion between the crust and the hot spot location. As the Pacific Plate moves relative to the hot spot, old pathways to the surface that were at one time directly over the hot spot eventually become tortuous paths. The magma finds less tortuous paths, and these eventually become new shield volcanos. The space between the old and new shield volcanos just happened to be on a non-path to the surface. $\endgroup$ – David Hammen May 5 at 2:30
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Don't be mislead by the subaerial part, it is actually a ridge on a large scale but neither the lava production rate nor erosion rates are constants. That leaves the ridge with higher and lower parts, as well as gaps. Furthermore reef building biocenoses change shape and appearance of the eroding volcanic edifices.

Hawaiian (and other like for instance the Canarian) volcanoes go through stages during their lifetime with different production rates and magma composition. Connections to the magma chamber(s) may remain in place for some time while the volcanic edifice moves relative to the magma source(*), until it has moved so far away that rising magma seeks new ascent channels to rise and deformation forms new dykes and cracks and so it may erupt from different vents, and that from a possible complex and subdivided magma chamber(s) fed by the plume underneath.

That process may leave an appearance of single detached volcanoes like e.g. M. Loa and M. Kea, but they are just similar things at different stages. Many volcanoes never reach a subaerial state and remain submerged, contributing to the appearance of detached islands.

(*) i would say, whether it is the plate that moves or the plume or the connections between plume and magma chambers is mostly irrelevant. Base argument is that the rate is not constant and eruptions may seek different paths during time. As to the exact why and how, that's ongoing discussion.

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  • $\begingroup$ You might want to make a brief comparison to subduction arcs. For example, Japan (well, Honshu at least) is a continuous strip of land because of volcanism along a large front, not just one hot spot. $\endgroup$ – Spencer May 12 at 17:08
  • $\begingroup$ Hi. Sure, post a question and we discuss arc volcanism. Cool (i mean hot) stuff :-) $\endgroup$ – user20217 May 13 at 8:54

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