1. Earthquakes and Volcanoes

2. Plate Movement What causes the motion of tectonic plates?
asthenosphere

3. Plate Movement What causes the motion of tectonic plates?
Convection (hot rock rises; cool rock sinks)
Tectonic plate movements are so slow and gradual that you can’t see or feel them
The movement is measured in roughly 2 centimeters per year.

4. Tectonic Plates and Volcanoes

6. Pacific Ring of Fire
An area where volcanoes and earthquakes are very common

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8. Volcano Formation
About 80% of active volcanoes on land form where plates collide (subduction)
About 15% form where plates separate

9. Hot spot volcanoes - hot mantle plumes breaching the surface in the middle of a tectonic plate (Hawaiian island chain)
The tectonic plate moves over a fixed hot spot forming a chain of volcanoes.
The Hawaiian island chain are examples of hotspot volcanoes.
Photo: Tom Pfeiffer /

10. The volcanoes get younger from one end to the other.

11. Plate Tectonics and Earthquakes

12. Earthquakes can occur at all three types of plate boundaries.
As tectonic plates push, pull, or slip past each other, stress increases along faults near the plate’s edge. In response, energy is released, and the earth is deformed
Figure showing the distribution of earthquakes around the globe

13. Deformation is the bending, tilting, and breaking of the Earth’s crust; the change in the shape of rock in response to stress
Most earthquake activity happens along the edges of tectonic plates; where a large number of faults are located
Sometimes, earthquakes happen along faults in the middle of tectonic plates
The black dots on this map of the world depict where earthquake activity is occurring. You can see that, as with volcanoes, the earthquakes are NOT randomly distributed around the globe. Instead they occur in linear patterns associated with plate boundaries.
(Note this diagram of earthquake distribution closely resembles the Pacific Ring of Fire distribution of volcanism).

14. A focus is the point inside the Earth where an earthquake begins
The epicenter is the point on the Earth’s surface directly above an earthquakes starting point