Student Page 5.2B: Convection Currents
Convection Currents
When a burner heats water in a pan or beaker, the
hot water rises from the bottom. When the hot
water reaches the top, it cools a little and is pushed
to the side by hot water rising from below. The hot
water then cools some more and sinks back down
to the bottom. This makes a current, or flow, of
water in the container. Hot water rises, moves to
the side, cools, and sinks. This process is repeated
over and over again. This process is called
convection. The flow of water in the container is a
convection current.
What does this have to do with
moving plates?
Continents are parts of plates, and plates are
pieces of the lithosphere. Plates float, but
they do not float on the ocean. They float on
the asthenosphere. They move wherever the
asthenosphere pushes them.
There are convection currents inside Earth that
work in the same way as the ones in a heated
container of water. Earth is hottest in the middle.
Hot magma in the mantle rises. As it reaches the
asthenosphere, it moves to the side and cools.
Then it sinks back down into the mantle. It is then
heated again and rises. The rising magma pushes
against the plates on the surface. They split apart
and move.
[illustration courtesy
USGS This Dynamic
Earth]
[illustration adapted from USGS This Dynamic Earth]
Student Page 5.2B: Convection Currents 249