I-5 Notes Dynamic PlanetI-5 Notes Dynamic Planet

The Nature of EarthquakesThe Nature of Earthquakes

FaultFault

• A fracture or fracture zone along which there has been displacement of one mass of rock relative to another, parallel to the fracture

• Fracture may extend for tens of kilometers

• When rocks break, the rocks on either side of the fracture plane slide past one another producing strong vibrations (felt as Earthquakes)

• Over time fractures may heal

Earthquakes and Plate MovementsEarthquakes and Plate Movements

• Largest earthquakes occur along subduction zones

• Earthquakes range from shallow to as deep as hundreds of kilometers

• Earthquakes also occur at continent-continent collision zones

Earthquakes along a transform Earthquakes along a transform boundaryboundary

• If fault locks for a long time & suddenly slips, it will produce a major earthquake

• If fault slips continuously, produces a very minor earthquake

• The San Andreas Fault is locked in the vicinities of Los Angeles and San Francisco

The Nature of VolcanoesThe Nature of Volcanoes

• Rock deep in the Earth melts to magma

• Magma rises because it is less dense than surrounding rock

• Rising magma may crystalize to rock again OR rise to surface forming a volcano

• The most important factor in how volcanoes erupt is the gas content of the magma

• Low gas content – magma flows peacefully down the sides of the volcano without a violent eruption

• High gas content – powerful explosion

Volcanoes and Plate MovementsVolcanoes and Plate Movements

• Volcanoes are formed along the mid-ocean ridges

• These volcanoes are very numerous

• Most are deep in the ocean

• If activity is strong enough, may build an island above sea level (Example – Iceland)

• Most large volcanoes occur along subduction zones

• Scientists think this is caused by parts of the subducting ocean crust reaching a certain depth & melts OR

• At a certain depth down, water is released from the rocks rising up above the subducted plate (water lowers the melting point of the mantle rock)

Hot Spot VolcanoHot Spot Volcano

• Hot spots in the mantle generate magma for a long period

• The hot spots don’t move

• Plates move over the hot spot

• The orientation & age of a line of hot spot volcanoes reveal the direction and speed of plate movement

• Volcanoes may occur far from plate boundaries

• The Hawaiian Islands & Yellowstone Park

The Association of Earthquakes The Association of Earthquakes and Volcanoesand Volcanoes

• Subduction Zones – major earthquakes, large volcanoes

• Most of the Pacific Ocean is rimmed with subduction zones

• The Ring of Fire

Continent-Continent CollisionContinent-Continent Collision

• Earthquakes are common

• No volcanoes are formed

• Examples, Southern Asia (China, India, Iran, & Turkey)

Mountain BuildingMountain Building

• Most of the world’s large mountain ranges are where two plates collide

Subduction ZoneSubduction Zone

• Magma from deep rises to feed volcanoes on the plate that is not subducting

• Crust near subduction zone grows in volume

• Example – Andes Mountains

Two Continents CollideTwo Continents Collide

• Lithosphere becomes thicker, so rises up to form mountains

• Himalayas

• Use your notes to fill in the following chart:

Earthquake Volcano Mountain

Divergent Boundary

Subduction Zone

Continent-Continent Collision

Transform Boundary

• Volcanoes are caused by the rise of magma formed within the Earth. Magma rises because it is less dense than the surrounding rock. The rising magma does not always reach the surface, but when it does, it forms a volcano.

• If the gas content of the magma is low, the magma erupts gently. If the gas content of the magma is high, an explosive and violent eruption can occur.

• Volcanism at a hot spot can occur far from a plate boundary, whereas volcanism at a mid-ocean ridge occurs at a plate boundary (a divergent boundary). Both types of volcanism involve the production and release of magma.