Earthquakes & Volcanoes

Remember from Last Lesson: Convergent Boundary – rocks are compressed as they come together causing one plate to slide under the other. Divergent Boundary – Plates are moving apart. Transform Boundary – Plates slide against each other

Constructive Mechanisms Construct means to build up. Forces that build up features on the surface of the Earth. Sediment (Deltas, sand dunes, etc.) Volcanoes (makes Islands) Tectonic Plates (Mountains) Crust deformation (Folding or Faulting)

Destructive Mechanisms Destruct means to destroy. Forces that destroy features on the Earth’s surface. Erosion (water - rivers and oceans, wind) Weathering (chemical or mechanical) Impact of organisms Earthquake

At the Faults Faults – are cracks or breaks in Earth’s lithosphere along which movement takes place. The pressure builds up under finally energy is released and the plates will shudder and jolt into a new position.

Folds Folds – Folds are bends in the Earth’s lithosphere.

Earthquakes Violent shaking of Earth’s crust. The release of built-up energy along a fault causes the Earth to shake. Richter Scale – the scale used to measure the size or magnitude of an earthquakes energy

Measurements Seismograph – instrument that measures the strength of a seismic wave moving through Earth’s crust. Seismic Waves – shock waves of energy sent out as the crust shakes.

Intensity Measured by what people can see & feel Focus – the point underground where the faulting occurs. Epicenter – point on the surface directly above the focus. Intensity is strongest at the epicenter because the seismic waves are strongest

Santa Cruz Mountains (Loma Prieta), California 1989 10 18 00:04:15 UTC (Local 10/17/1989) Magnitude 6.9 Intensity IX

Damage from a Tsunami that hit Hawaii

Volcanoes A vent in Earth’s crust where magma can escape. Rocks, hot gases, rock fragments, and ash burst forth, or erupt out Volcano – comes from the ancient Roman god of fire, Vulcan Start 37 – 100 miles below surface Rock melts and is called Magma

After the eruption The volcano collapses into a bowl-shaped mouth called a crater At the bottom of the crater lies the central vent Most volcanoes have repeated eruptions At times volcanic material may push out through side vents.

Classes of volcanoes

Shield Volcanoes Shield Volcanoes - gentle sloping, caused by hotspots or divergent plate boundaries. Formed when a lot of lava flows smoothly from a vent & spreads to cover a wide area. Creates a broad, low, dome-shaped volcano Mauna Loa - Hawaii

Cinder Cones Form when rock fragments erupt and are deposited around the vent. This creates a cone-shaped volcano with steep sides. Cinder cones in the caldera of Mt. Haleakala on Maui, Hawaii

Composite Volcanoes Composite volcano- Cone shaped with steeper sides than those of a shield cone, but not as steep as a cinder cone Mount St. Helens, Washington

The Ring of Fire Many earthquakes & volcanoes occur in a zone that borders the Pacific Ocean This area is known as the Ring of Fire Outlines Earth’s subduction zones The Pacific Plate converges with several continental plates to form the Ring of Fire