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EARTH’S INTERIOR TECTONICS, EARTHQUAKES & VOLCANOES INTERIOR STRUCTURE • The Earth is divided into several layers based on similar temperatures, materials, pressure, and depth INTERIOR STRUCTURE The materials that make up the Earth separated as the Earth cooled. The lighter materials rose to the surface and the heavier materials sunk to the center. Movement of heavy metals in the liquid outer core is responsible for the Earth’s magnetic field. INTERIOR STRUCTURE The mantle of the Earth is made of a mixture of hard, rigid rocks in the lower mantle and plastic, more flexible rocks in the upper mantle. HOT MATERIAL RISES, COOL MATERIAL SINKS The differences in temperature between the upper and lower portions of the mantle plus the flexibility of the upper mantle cause currents of material that move the crust above the mantle. INTERIOR STRUCTURE The crust of the Earth is broken up into sections called tectonic plates made up of the lithosphere. INTERIOR STRUCTURE Oceanic crust is heavier and more dense so it sinks and stays below the water. Continental crust is lighter and less dense so it rises above the water. PLATE TECTONICS • Geologist have known that the Earth’s landmasses have not remained in the same place throughout time • Early mapmakers first considered the idea that the continents have moved because of the similarity of coastlines between certain continents. PLATE TECTONICS • History of plate movement based on current evidence. PLATE TECTONICS History of Discoveries • 1500’s Abraham Ortelius(Dutch) noticed the fit of the continents surrounding the Atlantic Ocean and proposed (incorrectly) that the continents became separated by a series of earthquakes and floods • 1800’s Eduard Suess(Austrian) proposed that the Southern continents had once been joined in a single landmass PLATE TECTONICS • 1900’s Alfred Wegener(German) hypothesized that all the landmasses fit together in a supercontinent called Pangea in his 1912 publication • He reasoned that as the supercontinent broke apart the geologic structures fractured leaving small gaps along what would otherwise be matching coastlines • He found evidence on the modern continents to support his theory of an ancient supercontinent PLATE TECTONICS Continental Drift Hypothesis: states that the continents had once been joined to form a single supercontinent (Pangaea) and began to break apart 200 million years ago to form the present landmasses Evidence to support the hypothesis: - Continent shapes - Fossils - Geologic Patterns - Climate Patterns PLATE TECTONICS Continent Shapes: - Scientists have studied the shorelines of continents to see how they may have fit together - The most obvious connection lies between Africa and South America PLATE TECTONICS Fossils: - The same fossil groups have been found on separate continents with distances too great for organisms to travel if the continents were in the same places. PLATE TECTONICS Geologic Patterns: - Similarities in mountain ranges show that the mountains on separate continents may have been formed when they were joined together NOW THEN PLATE TECTONICS Climate Patterns: - Glacier evidence on all of the modern day continents suggest that the continents all fit together and were located around the area of modern day Antartica PLATE TECTONICS Wegener’s Missing Pieces • Explanation of WHAT caused the continents to move • Explanation of HOW the continents continued to move He was never able to answer these two questions in his lifetime. He froze to death on an expedition to Greenland still investigating evidence to support his hypothesis. PLATE TECTONICS • After Wegener’s death in 1930 scientists continued to search for the mechanisms behind his continental drift hypothesis • Shortly after his death Arthur Holmes proposed that mantle convection was the driving force behind the movements of the continental landmasses. His theory was proven correct but not until years after his initial proposal. Arthur Holmes 1890 - 1965 PLATE TECTONICS • Until the 1900’s the belief was that the ocean floor was completely flat and unchanging • During WWII submarine warfare and the use of SONAR began to prove this belief to be false when underwater mountains and valleys were mapped to help guide the submarines across the Atlantic Ocean PLATE TECTONICS • The maps of the ocean surface, sediment cores and magnetic readings after WWII confirmed that the ocean floor is constantly changing and shows evidence of the tectonic activity proposed by Arthur Holmes. PLATE TECTONICS Theory of Plate Tectonics: theory that helps explain the formation and movement of the tectonics plates which make up the Earth’s crust This led to the formation of the modern day landmasses and their current locations. PLATE TECTONICS Modern day plate sizes and locations: PLATE MOVEMENT • Plates meet at locations called plate boundaries. • Where these plates meet movement causes activities like earthquakes, volcanoes, and mountain building PLATE MOVEMENT Divergent Boundaries: places where the tectonic plates are moving apart Examples: mid-ocean ridges, rift valleys PLATE MOVEMENT Divergent Boundaries Seafloor spreading: as oceanic plates move apart new ocean floor is built by cooling lava PLATE MOVEMENT Divergent Boundaries Continental Rift Valleys: places in the middle of a continental plate where spreading is occurring PLATE MOVEMENT Convergent Boundaries: plate boundaries where two plates are moving together - Types of convergent boundaries rely on the type of crust that is being moved together PLATE MOVEMENT Convergent Boundaries Oceanic vs. Continental -forms where a piece of oceanic crust is subducted (pulled under)beneath a section of continental crust Subduction zone: Ocean plate slides under continental plate and forms a deep-ocean trench and continental volcanic arc PLATE MOVEMENT Convergent Boundaries Oceanic vs. Oceanic - Forms when one oceanic plate is subducted under another oceanic plate. - Creates a deep ocean trench and a volcanic island arc PLATE MOVEMENT Convergent Boundaries Continental vs. Continental - Forms when two continental plates collide and form mountain ridges PLATE MOVEMENT India and Eurasia Collision PLATE MOVEMENT Transform Fault Boundary: plate boundary where two plates move past each other along a fault (break in the crust) - High numbers of earthquakes occur in these areas Example: San Andreas Fault PLATE MOVEMENT What causes this movement? Isostasy: the idea that the upper mantle of the Earth is elastic and will adjust to the weight of the plates above it ISOSTASY ANIMATION PLATE MOVEMENT What causes this movement? Convection currents: circulation of molten rock within the mantle. As hot magma rises and cool rock sinks plates begin to move EVIDENCE OF PLATE TECTONICS The Earth supplies evidence for plate tectonics on a daily basis because it is constantly changing. Map of worldwide earthquake and volcano activity. - Tectonic activity like seafloor spreading, earthquakes and volcanoes are the best source of evidence to prove the plate tectonics theory EVIDENCE OF PLATE TECTONICS Earthquake: shaking and trembling that results from sudden movement of part of the Earth’s crust Reasons Why Earthquakes Occur: - Volcanic eruption -collapse of a cavern -impact of meteor -major cause: stress that builds up and causes faulting TECTONIC CHANGES Tension Stress: a force acting on a material Compression Tension: stress that pulls apart Shear Compression: stress that pushes together Shear: stress that twists TECTONIC CHANGES Stress: the force that acts on a material CAUSES Strain: a weakening or change in a material TECTONIC CHANGES 2 types of Strain • Elastic – material deforms and then goes back to its original shape after the stress is removed • Like a rubber band • Ductile – material deforms and stays deformed after the stress is removed • Like play-doh TECTONIC CHANGES Fault – a fracture or break in rock that happens when stress is applied too quickly or strain is too great • Faults are often concentrated around plate boundaries •When stress is relieved around a fault it causes an earthquake TECTONIC CHANGES Normal Fault: tensional stress pulls plates apart and stretches the Earth’s crust TECTONIC CHANGES Reverse fault: compression stress pushes the plates together and squeezes the crust TECTONIC CHANGES Strike-Slip fault: shear stress forces plates to move past each other EARTHQUAKES When the stress becomes too much the plates experience a sudden shift and release of energy. Elastic Rebound Theory: theory that explains how rocks that are strained past a certain point will fracture and spring back to their original shape EARTHQUAKES • Earthquake Anatomy Epicenter: point on Earth’s surface directly above the focus Focus: point beneath the Earth’s surface where the rocks break or move apart EARTHQUAKES Earthquake Wave Motion P Waves: -move fastest -move through solid, liquid or gas -push-pull waves EARTHQUAKES Earthquake Wave Motion S Waves: -travel slower -move side to side -travel through solids EARTHQUAKES Earthquake Wave Motion L Waves: -move slowest -move like ripples on a pond -move only through the crust EARTHQUAKES Earthquake Wave Motion Earthquake information is picked up by seismic recording stations around the world. Seismograph: instrument that detects and measures seismic waves EARTHQUAKES P waves travel faster so they arrive first followed later by S waves. The further the distance from the epicenter the longer the time between earthquake waves. Blue lines = primary waves Red lines = secondary waves EARTHQUAKES Seismogram: seismograph’s record of waves; shows vibration lines from the shaking motion of the earthquake waves The amount of time between the P and S waves indicate how far from the epicenter the recording station is. EARTHQUAKES • The distance from the epicenter can be calculated using the arrival times for the P and S waves and then pinpointed using information from 3 or more recording stations. EARTHQUAKES Where 3 circles from 3 separate recording stations overlap, a smaller approximate epicenter can be located. EARTHQUAKES Common Earthquake Locations • Most earthquakes occur along plate boundaries Pacific ring of fire: an area surrounding the pacific ocean with a high concentration of earthquakes and volcanoes. EARTHQUAKES Richter scale: scale that measures how much energy an earthquake releases (magnitude)by assigning a number from 1 to 10 TECTONIC PLATE MOVEMENT Tsunami: series of large waves caused by the displacement of a large volume of water - Often triggered by earthquakes, volcanic eruptions, landslides, or glaciers breaking EVIDENCE OF PLATE TECTONICS Volcanism: any activity that includes the movement of magma toward the surface of the Earth Volcano: a place where magma comes to the surface VOLCANOES Volcanic Zones SUBDUCTION ZONE - Most common volcanic area - Usually explosive and with lava eruptions MID-OCEAN RIDGE - Slow, fluid eruptions VOLCANOES Volcanic Zones Hot spots: areas of volcanic activity in the middle of a lithospheric plate VOLCANOES Anatomy of a Volcano Vent: any opening that brings magma to the surface Crater: funnel-shaped pit or depression at top of a volcano Caldera: collapsed crater after a volcanic eruption VOLCANOES Famous Calderas Yellowstone Volcano, United States Santorini Caldera, Greece VOLCANOES Volcanic Eruptions STAGE 1: sudden shallow earthquakes and rapid uplift of the ground surface Yellowstone uplift STAGE 2: cracking of the ground surface, and possible evaporation of the overlying groundwater VOLCANOES Volcanic Eruptions STAGE 3: eruption of lava and volcanic ash cloud VOLCANOES Volcanic Material pyroclastic material: solid fragments ejected from a volcano VOLCANOES VOLCANOES VOLCANOES Volcanic Material lava: magma that reaches the surface Magma: molten rock deep underground * Main difference: temperature, viscosity and the amount of gas VOLCANOES Lava Types Some lava cools with a smooth, solid surface Hawaii: Pahoehoe Some lava cools with sharp, jagged edges Hawaii: Aa VOLCANOES Types of Volcanoes • Shield Volcanoes -composed of quiet lava flows -form gently sloping, dome- shaped mountain -basaltic (mafic) magma VOLCANOES Types of Volcanoes • Cinder Cone Volcano - Made mostly of tephra and other rock particle - Formed from explosive eruptions - Not very high, narrow base, steep sides - Grantic (felsic) magma VOLCANOES Types of Volcanoes • Stratovolcano (Composite volcano) - built up of alternating layers of rock and lava - explosive eruptions at first with tephra, then quiet with lava - forms large, cone-shaped mountains - made of grantic and basaltic magma