Earthquakes & Volcanoes

Chapters 5 & 6

Faults

•      When rocks break, they move along faults

•      Applied forces cause rocks to undergo elastic deformation

•      When elastic limits are passed, rocks break

Faults

•      Rocks on one side of a fault can move up, down, or sideways in relation to the rock on the other side of the fault

 

Faults

•      Faults occur because forces inside the Earth cause Earth’s plates to move, placing stress on or near the plate edge

•      Rocks will bend, compress, stretch, and possibly break

Earthquakes

•      An earthquake is a vibration produced by  breaking rock

•      Rocks break, move along the fault, and then return to original shapes

•      Rocks on one side of a fault can move over, under, or past each other along fault lines

Forces on Rocks

•      Three types of forces act on rocks

–   Tension, compression and shear

•      Tension forces result from a normal fault

–   Caused by rock above the fault moving downward in relation to the rock below the fault

Forces of Rock

•      Compression forces result from a reverse fault

–   Forces squeeze rock above the fault up and over the rock below the fault

Forces on Rock

•      Shear forces are caused by a strike-slip fault

–   Rocks on either side of the fault move past each other without much upward or downward motion

Seismic Waves

•      Seismic waves are waves generated by an earthquake

–   Can move the ground

•    Forward and backward

•    Up and down

•    Side to side

•      The focus of an earthquake is the point of energy release

–   Where the rocks first break

•      The epicenter is the point on the surface directly above the focus

Seismic Waves

•      A seismic wave’s speed and direction change as the wave moves through different layers

–   Density increases with depth as pressure increases (move faster when more dense)

–   When waves hit materials with different densities, they bend, slow down, or stop

Volcanoes

•      A volcano is an opening in the Earth that erupts gases, ash, and lava

•      Volcanoes form when magma flows out of a surface opening called a vent

•      A steep-walled depression around the vent is called a crater

Energy in Volcanoes

•      The amount of water vapor and other gases present helps determine whether a volcanic eruption will be quiet or explosive

•      When gasses are trapped in magma, they lead to an explosive eruption

•      Magma with lots of water vapor trapped can cause an explosive eruption

Energy in Volcanoes

•      The composition of magma helps determine whether a volcanic eruption will be quiet or explosive

•      Low-silica magma produces a quiet, non-explosive eruption

•      High-silica magma produces an explosive eruption

Tectonic Plates

•      Volcanoes often form where plates are moving together or moving apart

•      The Mid-Atlantic Ridge is a divergent plate boundary that forms rifts through which lava can flow

Tectonic Plates

•      At convergent plate boundaries, volcanoes tend to erupt more violently than they do in other areas

Tectonic Plates

•      At the boundary between Earth’s mantle and core, unusually hot areas form hot spots, such as at the Hawaiian Islands