Plate boundary motion and earth processes: guided notes

Introduction

Plate motion leads to some of the most powerful events on Earth, including

• volcanoes

• earthquakes

• tsunamis

Volcanoes: what is a volcano?

A volcano is a vent or fissure ( crack) in the Earth’s surface through which molten rock and gases are expelled

• molten rock below the surface is called magma

• molten rock on the Earth’s surface is called lava

  VOLCANO LOCATIONS

  Most volcanoes occur near convergent and divergent plate boundaries

How Volcanoes Form ( At divergent boundaries)

• tectonic plates move away from each other

• creates a rift zone called a rift valley

• mantle rock rises to fill the gap

• decreased pressure cases magma to form

How Volcanoes Form ( At convergent boundaries)

• plates collide with each other

• when oceanic and continential plates meet, subduction occurs

• subduction created magma through increased temperature and pressure

Hot Spots

• caused by a mantle plume

• magma rises through the lithosphere to make a volcano

• the tectonic plate keeps mmoving and the “ hot spot “ stays still

• examples: hawaii and yellowstone

Geysers and Hot Springs

Magma close to Earth’s surface heats up water in the ground

If the boiling water gets restricted in the rock, it becomes pressurized and it will shoot out as a geyser.

Hot springs are home to unique bacteria, the only life that can live in them.

Hydrothermal Vents

Form at any volcanically active areas under the ocean- including mid-ocean ridges and near subduction zones

Ocean water seeps into cracks in the lithosphere and gets super heated by magma

The heat causes chemical reactions to occur, which makes the water more acidic and able to dissolve metal minerals in the rocks.

Earthquakes: What is an Earthquake?

An earthquake is the shaking of Earth’s surface from a release of energy.

Causes of Earthquakes::

• tectonic plates move in different directions and at different speeds. ( divergent, convergent, transform.)

• this created features called faults in the Earth’s crust

• A fault is a break in the Earth’s crust.

• Deformation is the change in the shape of rock in response to the stress of bending, tilting, and breaking of the Earth’s crust.

How Earthquakes Occur

• stress increases along faults near the edges of plates

  • Rock deforms in two ways:

• plastic manner ( like clay)

• elastic manner ( like a rubber band) ( demo in class)

• Elastic rebound energy releases energy as seismic waves

• Plastic deformation does NOT lead to earthquakes

• Elastic deformation DOES!!!

• Like a rubber band, rock can be stretched only so far before it breaks

Did you know that 1,571 earthquakes were big enough to be felt just in the last month??

**** Not all faults are at the edge of tectonic plates!! Also.. a lot of faults are from human activity!!!!

• some occur naturally in the lithosphere ( and crust )

• Example: New Madrid Fault System in Missouri

• Over 4,000 EQs since 1974

• Weakened areas from when Rodinia broke up ( a supercontinent prior to Pangea.. about 750 mya)

Most of the EQs humans have caused are from:

• mining

• oil/groundwater extraction'

• fluids injjected back into Earth

• weight applied where there wasn’t before