Earthquakes & Volcanoes Unit C Chapter 7 Lesson 2 C52 – C59

Objectives Recognize that most earthquake and volcanic activity occurs at or near plate boundaries. Recognize that different features are produced at different types of plate boundaries.

Remember from Lesson 1: Converging Boundary – rocks are compressed as they come together causing one plate to slide under the other. Diverging Boundary – Plates are moving apart. Sliding Boundary – Plates grind against each other (slide by each other).

At the Faults Faults – are cracks in Earth’s crust along which movement takes place. At faults rocks bend and fold or lock together in a jam. The pressure builds up under finally energy is released and the plates will shudder and jolt into a new position.

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.

Faulting Faulting – the movement of rocks along a fault. The rocks crack & split apart into blocks. The blocks continue to move in relation to each other This movement may cause further faulting.

Fault at Diverging Boundary The force stretches rock. The rock breaks & one block moves down along a sloping crack Mid-ocean ridges are typical locations See page C53 for diagram

Fault at Converging Boundary The force squeezes rock. The rock breaks, one block moves up along a sloping crack with the other moves down Occurs often in regions of subduction

Fault at Sliding Boundary Rocks grind against each other as they move horizontally past each other in opposite directions. Pressure builds up until the rocks break. San Andreas Fault in California is this type of fault.

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

Intensity Is measured by what people can see & feel on the surface 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 :04:15 UTC (Local 10/17/1989) Magnitude 6.9 Intensity IX

A man looks over apartment houses destroyed by a devastating earthquake in hard-hit Beichuan county, Mianyang city, Sichuan province, China, is seen Thursday, May 15, China warned the death toll from this week's earthquake could soar to 50,000.

Seismic Waves Two Types Body Waves – (P waves) & (S waves) - travel through Earth’s interior Surface Waves – (L waves) – travel along Earth’s surface

Body Waves ~ P waves Can travel through Earth’s interior in less than an hour Pass through solids & liquids As they pass through the liquid of the outer core they change directions As they return to Earth’s surface they cause back-and-forth motions of rock

Body Waves ~ S waves Travel slightly slower than P waves When they reach Earth’s surface they cause it to move up and down They can travel ONLY through solids When they pass through the mantle to the liquid core they lose their energy and do not return to the surface

Surface Waves ~ L waves Travel slower than body waves Do not travel far from the epicenter But they cause the most damage because they make the ground swell and roll like ocean waves Buildings fall, roads heave up, bridges collapse, rivers change course, cliffs tumble At sea, massive waves are set in motion (90ft high)

Damage from a Tsunami that hit Hawaii

Volcanoes An opening in Earth’s surface through which melted rock, hot gases, rock fragments, and ash burst forth, or erupt Volcano – comes from the ancient Roman god of fire, Vulcan Start 37 – 100 miles below surface Rock melts and is called Magma

Formation Gas is released when rock melts Mixes with magma (makes it lighter than the solid rock around it) Magma rises, melting more rock forming a chamber Pressure causes magma to find a vent to release

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.

Three main types of volcanic material ejected: Magma Dust, ash, and large rock chunks Gases

Magma Called LAVA when it hits the surface Can be fast and liquid like or slow and thick Hotter than 2,000 F Cools and forms boulders, domes, cones, tubes, smooth & jagged sheets

Dust, Ash, Rock Rock fragments form when gas in magma cannot escape Pressure builds up and gas blasts magma apart Fragments erupt into dust, ash, and large chunks called “bombs” Lava Bombs, Lassen Volcanic National Park, California

Gas Mostly steam is released Also poisonous chemicals These gases mix with ash to form a deadly black smoke Large fumarola (volcanic gas outlet) in Mutnovsky Volcano Crater (Russia)

Shield Volcanoes Form 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 Cone shaped The sides are steeper 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

Ring of Fire ~ Volcanoes As the subducting plate sinks into the mantle, it melts to form magma. Magma later rises to the surface as a line of volcanoes On the ocean floor, a deep narrow valley called an ocean trench may form along a subduction zone Volcanoes often parallel the trench

Ring of Fire ~ Earthquakes Faulting at diverging boundaries causes earthquakes & can create volcanoes. Diverging boundaries are usually located near the middle of ocean basins Faulting at the ridges leads to earthquakes.

Built up energy is released along a fault during a(n) ____________. Earthquake

Intense vibrations felt throughout Earth’s crust during an earthquake are called _________. Seismic Waves

_____ is melted rock found beneath Earth’s surface. Magma

Both earthquakes and volcanoes often occur along ______, which are cracks in Earth’s crust. Faults

Where do most of Earth’s volcanoes and earthquakes occur? Along plate boundaries

Which best describes the surface waves produced by an earthquake? A. They move more slowly than body waves B. Move more quickly than body waves. C. Travel a great distance from the epicenter D. Cause relatively little damage

Which best describes the surface waves produced by an earthquake? A. They move more slowly than body waves

_________ form when lava spreads out to cover a large area. Dome mountain