Earthquakes and Volcanoes

EARTHQUAKES Plate Tectonics Lithosphere – the crust and upper part of the earth’s mantle Inner Core Outer Core Mantle Crust 4 3 1 2

EARTHQUAKES Plate Tectonics Plates – large pieces of the lithosphere Theory of plate tectonics – the idea that the earth’s crust is made of moving plates Plate Boundaries – places where the plates meet Scientists think as the magma in the Earth’s mantle moves, it causes the plate boundaries to collide, separate or slide along each other.

EARTHQUAKES Plate Tectonics Scientists believe the Earth is made up of large plates that float on the partly melted rock of the Earth’s mantle. Pangaea – a large landmass that some scientists think may have existed at one time No recorded observations

EARTHQUAKES Causes of Earthquakes Earthquakes often occur when rocks along the plate boundaries shift suddenly and release stored energy. Construction of large buildings and the movement of molten rock under a volcano can also cause earthquakes.

EARTHQUAKES Causes of Earthquakes Faults – breaks in the earth’s surface along which rocks can move Three kinds of faults – determined by how the rocks move against each other (thrust or reverse fault, normal fault, strike-slip fault) Reverse fault – rocks push together until a section of rock moves upward

EARTHQUAKES Causes of Earthquakes Three kinds of faults – determined by how the rocks move against each other (thrust or reverse fault, normal fault, strike-slip fault) Normal fault – rocks moving apart Strike-slip fault – rocks moving horizontally past each other

EARTHQUAKES Earthquake Waves Earthquakes occur below the surface of the earth. Focus (A) – beginning point of an earthquake Seismic waves – vibrations that flow out from the beginning point of an earthquake Epicenter (B) – the point on the surface of the earth directly above the focus

EARTHQUAKES Earthquake Waves Body waves – seismic waves that occur beneath the surface of the earth P Waves – primary waves; fastest moving; travel in a straight path by a push and pull motion; these waves move back and forth S Waves – secondary waves; move more slowly; move in an up and down zigzag pattern; causes the particles in the rock to vibrate to the direction in which the wave is moving

EARTHQUAKES Earthquake Waves Surface Waves: the slowest moving and most destructive waves Can move back and forth in a zig zag pattern; fastest moving land waves Can move in a circular pattern; rolling motion along the ground

EARTHQUAKES Detecting Earthquakes Seismograph – a machine that detects, times, and measures the movement of the earth Seismograms – records of the movements of the earth Seismologists – scientists who study the movement of the earth

EARTHQUAKES Measuring Earthquakes Mercalli scale – based on the amount of destruction caused to man-made structures Measures observable destruction Richter scale – measures the magnitude of an earthquake’s seismic waves and assigns it a number Magnitude – strength of the seismic waves of an earthquake, this is how much energy is released.

EARTHQUAKES Building for Earthquakes Features that help structures withstand earthquakes: Concrete reinforced with steel rods Foundation laid in rock Steel framing

EARTHQUAKES Related Disasters Tsunami – giant ocean waves triggered by earthquakes, volcanoes, or landslides Other catastrophic events associated with earthquakes: Volcanic eruptions Landslides

VOLCANOES Magma – molten rock under the earth Volcano – are a form of a mountain, they occur when a crack in the earth’s surface allows magma and gases to come to the surface Volcanologists – scientists who study volcanoes Magma chambers – pockets of molten rock in the earth’s lithosphere Lava – hot molten rock that breaks through the surface of the earth Vent – opening in the surface of the earth through which lava flows Crater – the bowl shape at the top of a main vent

VOLCANOES Causes of Volcanoes Volcanic ash – jagged bits of crushed rock Volcanic cone – funnel-shaped mound Draw this Diagram in your notes. Side Vent Vent Lava Magma Chamber 1 2 4 3 5

VOLCANOES Locations of Volcanoes Volcanic activity may occur under the ocean, at hot spots, along plate boundaries, and along the Ring of Fire. Ring of Fire – active volcanoes around the edges of the Pacific Ocean Under water eruptions (submarine eruptions) are 20x more frequent than eruptions on land Hot spots – places where a pool of very hot magma rises toward the surface and forms new land

VOLCANOES – Classifying By Shape Shield volcano – large, gradually sloping sides; erupts continuous flowing lava; mild, continuous eruptions Cinder cone – resembles a hill; has a bowl-like crater; usually has more than one vent; made of cinders Cinders – bits of ash and lava Composite cone – steep sides and layers of lava and tephra Tephra – a mixture of cinders, ash, and rock emitted by a volcano

VOLCANOES – Classifying By How Often They Erupt Volcanoes can have more than one kind of eruption because one eruption can change the conditions inside a volcano, causing it to erupt differently the next time. Active volcano – one that has erupted at some point during a recorded time period and is expected to erupt again Dormant volcano – has erupted in the distant past but is currently inactive and not expected to erupt again Extinct volcano – does not have a recorded eruption and is not expected to erupt in the future There is NO guarantee that it will remain extinct

VOLCANOES – Classifying By The Type of Eruption Hawaiian eruption – runny lava and little or no cinder, ash or steam; quiet; may continue for long periods of time Strombolian eruption – fountain of lava that runs down the sides Vulcanian eruption – violent; causes a loud explosion that sends lava, ash, cinders, and gas into the air Pelean eruption – produces a pyroclastic flow (avalanche of red-hot dust and gases emitted by a volcano) Plinian eruption – most powerful; spews lava, blows gases, ash, and debris into the atmosphere Pyroclastic flow – a high-speed flow of very hot gases and dust

VOLCANOES Effects of Volcanoes Vog – volcanic gases; volcanic fog; pollutes the air and can cause acid rain and respiratory problems The gases, ash, and dust of volcanoes can cause cooling in the weather. Dangers of Volcanoes Debris flow – when part of the mountain collapses and mud and rock fragments surge down the mountain Products of Volcanoes Soil rich in nutrients, valuable gems Igneous rock – formed as magma and lava cool and harden

VOLCANOES Effects of Volcanoes Other thermal eruptions Hot spring – a heated pool of warmed ground water Geyser – a hot spring that blows steam and water into the air Mud pots – a hot spring that contains more mud than water

Review for CFA #11 Earthquakes & Volcanoes Earthquakes occur along breaks in the earth surface, these breaks are called___________. List and Describe the 3 types. The _________is the beginning part of an earthquake & the ____________is the point on the surface of the earth directly above the focus. ________ ________ are the vibrations that flow out of the beginning point of an earthquake. List and Describe the 3 types. What are the 2 scales used to measure the strength of an earthquake? How do they differ? What is magnitude? What is a volcano? Where can volcanic activity occur? What is the ring of fire? What are some of the effects of a volcanic eruption? What types of geological events occur at plate boundaries?