3.2 Moving plates

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3.2 Moving plates

Learning objectives

After studying this section, you will be able to:

• Describe in which direction the tectonic plates move.
• Explain why earth’s tectonic plates move.

Which endogenous process moves the tectonic plates?

1. Oceanic ridge.
2. Divergence.
3. Convergence.
4. Convection currents.

Plates moving apart

Divergent plate boundary

Two tectonic plates which move apart (← →).

Oceanic ridge

Underwater mountains formed by a divergent plate boundary.

The Mid Atlantic Ridge is visible in Iceland.

Plates moving towards each other

Convergent plate boundary

Tectonic plates which move towards each other (→ ←). 

Mountain ranges
are created:

Areas which contain a lot of mountains.

This photograph is taken in Iceland. What does it show?

1. Subduction.
2. Collision zone.
3. Mid Atlantic Ridge.
4. Convection currents.

Collision zone = A convergent boundary between two continental plates.

Fold mountains

Large mountains formed by  the collision between two continental plates. 

What kind of plate boundary
can we find where two tectonic plates move towards each other?

1. Divergent plate boundary.
2. Convergent plate boundary.
3. Transform plate boundary.

Plates moving towards each other

Convergent boundaries also occur between oceanic plates and continental plates:

Subduction = Process where the oceanic plate dives under the continental plate.

Trench = Deep and narrow gap on the ocean floor. Formed by the subduction process.

What do we call the process when an oceanic plate moves underneath a continental plate?

1. Subduction.
2. Collision.
3. Oceanic ridge.
4. Divergence.

Plates sliding alongside each other

Transform plate boundary

Where 2 tectonic plates slide alongside each other (↑ ↓).

The San Andreas Fault (US) is an example of a transform plate boundary.

Convection currents

Convection currents rise up due to the heat in the inner core of the earth. It's the process which moves the tectonic plates.

Endogenous force = Force from within the earth.

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Other theories of plate movement

Before the 1990s, geologists explained plate movement using ridge push. Scientists thought that the mid-ocean ridges - high mountain ranges on the ocean floor - pushed on the areas of the tectonic plates further away from the ridge. In this way, the ridges created a movement away from the mid-ocean ridge. After the 1990s, this idea was seen as a part of the answer, together with slab pull.

New technologies give new suggestions about the mechanism behind the moving plates. Many geologists now believe that plate tectonics is caused mostly by slab pull: according to this theory, rock at the subduction zone sinks into the mantle due to gravity. As it sinks, it pulls the rest of the oceanic plate with it.

In which directions do tectonic plates move?

Why do the earth’s tectonic plates move?

Essence

There are three types of plate movement. Plates can move apart (diverge), they can move alongside each other (at a transform plate boundary) and they can move towards each other (converge). At a converging boundary between two continental plates, the plates collide, creating high mountains. At a converging boundary, between an oceanic plate and a continental plate, the oceanic plate will subduct. Tectonic plates move because convection currents carry them along.

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