system
Given the following post, respond as if you're commenting on Reddit:
human
If island chains like Hawai'i were formed by the continuous movement of a plate over a magma plume in the mantle, why do they take the form of separate islands rather than a continuous ridge?
gpt
To form a continuous line, you would have to assume that magma plumbing is continuous; that is that you apply magma at the base of the crust at position x and it comes out at y above, apply at x+1 and it will come out at y+1. That is not the case.

Magma plumbing is highly discontinuous; magma will preferentially propagate along fractures and pre-existing weaknesses in a system. A pool of magma accumulating at the base of the crust will tend to propagate along the same route it first successfully found. That route will be used until the low-level magma suipply is cut off. At this point a new low level accumulation will form, until it too finds itself a new plumbing route.

Consider too that the ocean floor is cut by numerous large faults which cut through pretty much the entire plate - these and their related structures can form preferentially weak loci for magma injection.

The vast majority of magma never even makes it out to the surface - most is simply crystallised at depth in magma chambers which dead-end several kilometres below the surface, or are injected as dykes or sills within the host strata.

It's a bit like considering the population living around a city, and thinking that you should be able to draw a straight line from their house to the centre, and that will be their route in, resulting in a perfectly radial distribution of travel. In reality, they move along main arterial roads because that is the *easiest* route, rather than climbing over fences, walking through other peoples houses, and navigating the *shortest* route.