Internal Forces Shaping the Earth discusses plate tectonics and how the movement of tectonic plates causes earthquakes and volcanic activity. Tectonic plates move in four main ways - spreading, subduction, collision, and shearing - which reshapes the Earth's surface over time. Earthquakes occur when plates suddenly slip or grind past each other at fault lines. Most earthquakes and volcanoes are located at boundaries where tectonic plates meet, such as the Ring of Fire around the Pacific Ocean.

1. Internal Forces Shaping the Earth

2. I. Plate Tectonics
A. The Earth Moves
1. Tectonic plates are massive, moving
pieces of Earth’s lithosphere.
2. Plates ride above circulating, heated
rock.
3. Geographers study plate movements to
understand:
a. how the earth is reshaped.
b. how earthquakes and volcanoes are
formed.

4. B. Plate Movement
1. Plates move in one of four ways:
a. by spreading, or moving apart.
b. subduction, or diving under another
plate.
c. collision, or crashing together.
d. sliding past each other in a shearing
motion.

5. 2. Movement of plates effects surface of
the earth.
3. Saudi Arabia–Egypt’s plates are
spreading apart, widening Red Sea.
4. India’s plate is crashing into Asian
continent, building up Himalayas.
5. Three types of boundaries mark plate
movement:.
a. divergent boundary
b. convergent boundary
c. transform boundary

7. D. Folds and Faults
1. Two plates meeting can cause folding,
cracking of rock.
2. Fault occurs when pressure causes rock to
fracture, or crack.
3. Fault line is place where plates move past each
other.

8. II. Earthquakes
A. The Earth Trembles
1. An earthquake occurs when plates grind or slip at a fault
line.
2. A seismograph detects earthquakes and measures the waves
they create.
B. Earthquake Locations
1. Location in the earth where an earthquake begins is called
the focus .
2. Epicenter—the point directly above focus on the earth’s
surface.
3. Nearly 95% of earthquakes occur at tectonic plate boundaries

9. C. Earthquake Damage
1. Earthquakes release energy in the form of motion,
causing:
a. Landslides
b. land displacement
c. fires (broken gas lines)
d. collapsed buildings
2. Richter Scale—numeric scale showing relative
strength of earthquake.
D. Tsunami
1. Tsunami, a giant ocean wave, begins at epicenter
of an earthquake:
a. travels at up to 450 mph.
b. waves of 50–100 ft. or higher.

12. III. Volcanoes
A. The Explosive Earth
1. Volcano—underground materials pour from crack in
the earth’s surface.
2. Most volcanoes occur at tectonic plate boundaries.
B. Volcanic Action
1. Eruption—lava, gases, ash, dust, explode from vent in
Earth’s crust.
2. Lava—magma that has reached the earth’s surface;
may create landform.

13. C. Ring of Fire
1. Ring of Fire—zone around rim of Pacific
Ocean:
a. meeting point of eight tectonic plates.
b. vast majority of the earth’s active volcanoes
located here.
2. ―Hot spots‖ are where magma rises to surface
from mantle.
3. Hot springs, geysers indicate high
temperatures in earth’s crust.
4. Some volcanic action is useful:
a. volcanic ash produces fertile soil.
b. hot springs are tapped for heat, energy.