Geology Reference
In-Depth Information
Chapter 10
Who's Driving This Thing?
Mantle Convection and Plate
Movement
In This Chapter
Exploring three models for what drives crustal plate movements
Connecting magma, volcanoes, and plate boundaries to convection
Realizing how plate movement causes earthquakes
One of the biggest challenges for Alfred Wegener when he proposed his idea that the con-
tinents had once been connected and were now moving apart (see Chapter 8) was de-
scribing a
mechanism,
or driving force, for continental movements. He supposed that the
continents just plowed through the ocean crust — like a whaling ship through sea ice —
as they careened around the globe crashing into one another. Today, we understand that
the continents above sea level are part of larger plates made of both continental crust
and oceanic crust (see Chapter 9), but how and why they move around is still somewhat
of a mystery.
Earth scientists now accept that the movement of crustal plates is very likely related to
convection
— the movements of heated materials — inside the earth. But they have not
agreed on
how
convection drives the plates. Currently there are three popular ideas
about how the convection of material beneath the earth's crust moves plates: the mantle
plume model, the slab-pull model, and the ridge-push model. (In Chapter 2, I explain that
models
are descriptive hypotheses ready to be tested.) In this chapter, you explore these
different convection-based models. I also explain how mantle convection and plate move-
ments create volcanoes. And finally, I explain how the movement of plates causes earth-
quakes and how studying earthquakes provides additional clues about the earth's interi-
or.
