22.4: Hot spot tracks
- Page ID
- 22785
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Remember that one of the errors Alfred Wegener made was to estimate too-fast rates of speeds for his drifting continents. Now that the idea of seafloor spreading had been established, a test could be made. Numerical dating of igneous rocks had become validated as a technique during the interregnum between Wegener’s book and Hess’s paper, and attention soon turned to island archipelagos such as Hawaii and the Galapagos.
Unlike volcanic island arcs, which feature a trench-parallel line of volcanoes all erupting at various times, on and off, over and over, Hawaii and the Galapagos are different. In each archipelago, the volcanoes show an age progression. At one end of the chain is an active volcano or two, erupting lava and ash in the present day. But as you work your way toward the other end of the chain, the volcanoes are inactive and more weathered. Sure enough, radiometric dating confirms our suspicion: they get older in one direction! In Hawaii, the volcanoes get older toward the northwest. In the Galapagos, the volcanoes get older toward the east. One explanation that has been offered to explain this age progression is that there is a source of magma unrelated to plate tectonics, piercing upward periodically with injections of magma as the plate of oceanic lithosphere moves steadily overhead. This simple notion has a simple name: it’s a hot spot.
Hot spot volcanism implies that if a plate, such as the Pacific Plate, is moving at a steady rate in a given direction over a stationary hot spot, periodically magma from the hot spot will burst through, making volcanoes on the surface of the plate, which will then trundle them along, away from the hot spot. The volcano will go dormant, begin to weather and erode, and will subside. To the northwest of the main Hawaiian islands are a series of seamounts: not nearly as much landmass pokes up above sea level, but they still represent a massive bump on the face of the Pacific Plate. Advocates of the hot spot interpretation for Hawaii would interpret these seamounts as places that used to be on top of the hot spot, but have long since been dragged away.
A kink in the seamount chain can be found northwest of the Midway Atoll, where the Emperor Seamount chain trends off toward the north. This reflects a change in direction of the Pacific Plate that took place around 48 Ma.
The Pacific is a fast-moving plate. In some places, it’s moving about 10 cm/year relative to a fixed frame of reference. Plates can dawdle along at a slower pace, too; For instance, the Atlantic is widening at only 2.5 cm/year. Even a fast moving plate is still too slow for the human eye to perceive. We frequently liken the pace of plate movement to the rate of fingernail growth. You can’t see it happen, but you know it happens. I suppose nail clippers are the subduction zone in that analogy…
Did I get it? - Quiz
Prior to the inception of GPS, how did hot spots help constrain plate motion?
a. When continents collide, the crust is thickened and gets hot, and this helps encourage the growth of metamorphic minerals -- minerals that can be numerically dated to figure out when the orogeny happened.
b. As a plate moved over a hot spot, every now and then a volcano (with numerically-datable minerals in its lavas) would erupt and solidify, and then be carried away.
c. The hot spots generated a magnetic field which was imprinted into the oceanic lithosphere.
- Answer
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b. As a plate moved over a hot spot, every now and then a volcano (with numerically-datable minerals in its lavas) would erupt and solidify, and then be carried away.
Which of the following is thought to be a hot spot volcanic track?
a. the Aleutian Islands of Alaska
b. Cuba, Hispaniola, and Puerto Rico
c. Hawaii and the Emperor Seamounts
d. the Great Rift Valley of East Africa
- Answer
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c. Hawaii and the Emperor Seamounts
How fast do plates move?
a. 2-20 m per year
b. 2-20 km per year
c. 2-20 cm per year
d. 2-20 mm per year
- Answer
-
c. 2-20 cm per year