Up to now it has been believed (and taught by textbooks) that hotspots stay fixed in one place just underneath the earth's crust. These hotspots are huge blobs of super-hot magma which often poke through the crust to form a volcano. Meanwhile, as the hotspot sits there stationary, a tectonic plate moves over them, forming a "conveyor belt" of volcano creation, one volcano after the next in a chain.
This chain of volcanoes, however, can take a turn if and when the tectonic plate a) rotates/turns/spins or b) changes the overall direction of its plate movement/drift.
Case in point: the bend/turn where the Emperor Ridge volcanoes (now extinct seamounts) become the Hawaiian ridge, a roughly 45° turn. From the above, we would assume that long ago when this turn came about the Pacific Plate either rotates or changed direction.
This is confirmed by this Univ. of Hawaii scientist http://www.soest.hawaii.edu/GG/ASK/plate-tectonics2.html who says
a) Pacific Plate is moving overall NW direction
b) Pacific Plate is also rotating around a point south of Australia.
A new theory
However--it turns out that scientists recently changed the theory. They now believe that it was the hotspot itself that moved. According to the article below, the hotspot itself moved southward under the lithosphere until 45 million years ago, creating the Emperor Ridge trail of volcanoes, then it stopped moving and became fixed in one spot. From that point onward, the overall plate moved NW creating the Hawaiian Ridge.
"A sharp bend in the chain about 2,200 miles northwest of the Island of Hawai'i was previously interpreted as a major change in the direction of plate motion around 43-45 million years ago (Ma), as suggested by the ages of the volcanoes bracketing the bend.
However, recent studies suggest that the northern segment (Emperor Chain) formed as the hot spot moved southward until about 45 Ma, when it became fixed. Thereafter, northwesterly plate movement prevailed, resulting in the formation of the Hawaiian Ridge "downstream" from the hotspot."
from
http://geology.com/usgs/hawaiian-hot-spot/
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