The Internal Processes Chapter 14 The Internal Processes

The Internal Processes Rigid Earth to Plate Tectonics Plate Tectonics Vulcanism Folding and Faulting Earthquakes

Rigid Earth to Plate Tectonics Questioning Theories of Rigid Earth Isostasy Continental Drift

Theories of Rigid Earth For billions of years Earth has been shaped and reshaped by internal processes Crust is folded, bent, lowered, raised Until 1950’s it was believed that Earth was “rigid” or static Now established that continents drift – plate tectonics

Igneous Rock Formation Igneous rocks form in two layers Sima = silica+magnesium; oceanic; denser Sial = silica+aluminum; continental; less dense Because sima is denser than sial, it subducts the continental plate at convergence i.e., it slides under the less dense plate.

Isostasy – Isostatic Rebound Crust “floats” on denser, deformable mantle Addition of considerable weight/mass causes crust to sink Removal of weight allows crust to rise Example: Glacial and Interglacial periods Accumulated ice Crust depressed Ice melts Weight removed Crust rebounds

Continental Drift 450 million years ago, there was only one land mass, Pangaea 250 million years ago, something happened to cause the plates to separate The separation has been ongoing to the present day Over millions of years, the shapes and positions of the continents have changed.

Continental Drift: Pangaea Continental drift is the movement of continents over the Earth's surface, and their change in position relative to each other. Original land mass with continental boundaries

Plate Tectonics Seafloor Spreading 3 types of Plate movement Divergent Convergent Transform Continental Rearrangement Accreted Terranes and Hot Spots

Plates - Seafloor Mid-Atlantic Ridge The Mid-Atlantic Ridge is an underwater mountain range that runs from Iceland to Antarctica. It is the longest mountain range on Earth. The ridge was discovered by Bruce Heezen in the 1950s. The discovery of this ridge led to the theory of seafloor spreading and general acceptance of Wegener’s theory of continental drift. The ridge runs along a divergent boundary. Plates - Seafloor Mid-Atlantic Ridge

Plates Earth's surface is broken into seven large and many small moving plates Each plate is about 50 miles thick Each plate moves relative to one another an average of a few inches a year Three types of movement are recognized at the boundaries between plates: convergent, divergent and transform-fault.

7 Major Plates Eurasion plate (which is covers Asia and Europe) North American plate (North America) South American plate (South America) Pacific plate African plate (Africa and Middle East) Australian plate Antarctic plate For the most part, each major plate represents one of the seven continents.

Major and Minor Plates

Plates with Topography

Plate Boundaries (a) Oceanic-Continental (b) Oceanic-Oceanic (c) Continental-Continental Be familiar with terms circled in red!

Convergent Boundaries Plates move toward each other and collide Where an oceanic plate collides with a continental plate, the oceanic plate tips down and slides beneath the continental plate forming a deep ocean trench (long, narrow, deep basin.) This is called subduction Subduction, occurs at the boundary between the oceanic Nazca Plate and the continental South American Plate. Where continental plates collide, they form major mountain systems such as the Himalayas.

Be familiar with terms circled in red! Subduction Be familiar with terms circled in red!

Divergent Plate Boundaries Plates move away from each other, as at the East African Rift Where plates diverge, hot, molten rock rises and cools adding new material to the edges of the oceanic plates This process is known as a rift valley Be familiar with terms circled in red!

Be familiar with terms circled in red! Seafloor Spreading Divergent Movement of Plates Sea-floor spreading is the creation of new oceanic crust at mid-ocean ridges And, the movement of the crust away from the mid-ocean ridges. Seafloor Spreading Be familiar with terms circled in red! Figure 14-5

Transform Plate Boundaries Plates move horizontally past each other Since the plates are sliding past each other, and not tearing or crunching, they lack the spectacular features found at convergent and divergent boundaries They are marked in some places by linear valleys along the boundary where rock has been ground up by the sliding In other places, they are marked by stream beds that have been split in half

Transform Plate Boundaries For example, the San Andreas Fault zone The Pacific Plate, on which Los Angeles sits, is moving slowly north westward relative to the North American Plate, on which San Francisco sits.

Formation of Accreted Terrane Small to medium mass of lithosphere carried a long distance by a moving plate Eventually converges with another plate Too buoyant to be subducted; it joins – accretes Often fragments in process Fragmented Accreted

Accreted Terranes added to western North America over the past 200 million years

Formation of Hot Spot Magma comes to or close to surface at interior plate location – not near plate boundary Hot spots are relatively stationary for 10-100 million years Create volcanoes or hydrothermal vents at surface

The Hawaiian Hot Spot A mantle plume here for millions of years As Pacific plate moved NW, volcanoes created and died, as source of magma shut off

Vulcanism Volcanism Distribution of Active Volcanoes Volcanic Hazards Intrusive Vulcanism

Vulcanism All phenomena connected with the origin and movement of molten rock Includes volcanic eruptions and solidification of molten material below the surface

Volcanism Volcanism is the expelling of magma onto Earth’s surface The magma is then called lava Pyroclasic material consists of: lava, rock fragments, solidified blobs of lava, ashes, dust, gas and steam Pyroclastic material is hurled upward and can be carried in the atmosphere for thousands of miles and over many years

Distribution of Active Volcanoes The heaviest distribution of volcanoes is the Pacific Ring of Fire

Calderas Produced when a volcano explodes, collapses or both Result is an immense basin shaped depression – usually circular Depression is many times larger than original volcanic vent

Kilauea, Hawaii The summit area of Kilauea volcano is dominated by collapse features. Kilauea caldera is a large collapse structure caused by rapid draining of magma between 1460-1500. Genovesa, Gallapogos Is. The island consists of a single volcano, which emerges only 200 feet above sea level A breached caldera on the south side of the island forms Darwin Bay A small lake-filled crater is located in the center of the island.

Volcanic Hazards Volcanic gases Lava flows Eruption column & cloud Pyroclastic flows Volcanic mudflow

Intrusive Vulcanism Shiprock, NM Magma solidifies beneath Earth’s surface and produces igneous rock Rock pushed up into crust, before or after solidification, is called igneous intrusion Shiprock, NM

Diastrophism Deformation of Earth’s crust by folding or faulting Term implies that material is solid and not molten Rocks bent or broken from extreme pressure in mantle or crust

Folding and Faulting Types of Folds Types of Faults Faulted Landforms Monoclines, Anticlines, and Synclines Overturned and Overthrust Folds Types of Faults Normal Reverse Strike-Slip Thrust Faulted Landforms

Folding Crustal rocks are bent and folded by forces, such as lateral compression

Types of Folds Monocline Anticline Syncline Overturned fold Overthrust fold

Syncline Fold

Faulting The breaking apart of rock material from crustal stress The crust on one or both sides of the break must move The movement can be vertical or horizontal or both Usually takes place in a fault zone Intersection of fault zone with Earth’s surface is called fault line

Types of Faults Normal Over thrust Reverse Strike slip

California Fault Line Calaveras Fault, Hollister CA Strike slip fault in the San Andreas fault system

Rift Valley Northern section of the Great Rift Valley. The Sinai peninsula is in center and the Dead Sea and Jordan River valley above Rift valley Africa

Earthquakes Earthquake Movement (waves) Magnitude and Shaking Intensity Hazards Prediction

Seismic Waves

Collision of India with Eurasia

Earthquake Waves

Faulting

Transform Faults

Folding

Seismographs

Breakup of Pangaea

Formation of Crater Lake

Igneous Features

Seafloor Spreading and Plate Boundaries

Tectonic Settings of Volcanic Activity

Terrane Formation

Animations http://www.pbs.org/wnet/savageearth/animations/index.html http://iri.columbia.edu/~lareef/tsunami/#Tsunami_Animation:_National_Institute_of http://www.geophys.washington.edu/tsunami/general/physics/characteristics.html http://esminfo.prenhall.com/science/geoanimations/animations/86_Tsunami.html