How Fast Do Plates Move?
ES0810  A Change in Plate Motion

The entire chain of islands and seamounts appears to have been built in the same way as the animation you saw in step 3 illustrated. Each feature in the chain is like a "scar" on the plate's surface, recording the plate's passage over the hot spot. As these features just ride along on the plate after they form, an arrow pointing from young features to older ones points in the same direction as the plate motion.

What about the bend in the chain, though? Think about or return to the animation from step 3, and imagine what it would take to create a bend in the line of volcanoes formed over the hot spot.

Jennifer Loomis, TERC
Seafloor topography of the Northwestern Pacific Ocean with ages of volcanic rocks.

8. What does the bend in the chain of seamounts indicate?

Though we've been focused only on the Pacific Plate, interactions among all the plates affect one another. A plate tectonic "traffic jam" in one part of the world, like a subduction zone that becomes the site of a continent-continent collision, could change the dynamics of plate motion all over the planet.

Click here to see an animation of continental locations over the past 150 million years. Step through the animation to observe the changes in plate motion that began around 40 million years ago. Look for an event that disrupted plate motions because continents could no longer move in the direction and speed they once maintained.

9. What global tectonic event might have been responsible for changing the direction of the Pacific Plate's motion? (What major tectonic event occurred around 40 million years ago?)


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