Plate Tectonics

By Nadine Kummer

Alfred Wegner’s theory of continental drift & Supercontinent theory

Continental drift Wegner’s theoryHis theory was that all the continents like we know them today were one big Supercontinent. He thought about it because some continents have similar shapes and he compared that with a newspaper. He called that the torn newspaper analogy. It means to put together all the pieces and see if they have same characteristicsStamp from

Austria

Click icon to add pictureEvidence

he explained it by showing the similarity between the land lines of south america and africa.It also explained some mountain chaines.

Problems with theory

the biggest problem was the supporting evidence. It was only a theory and he his only evidence were the landforms. Nothing scientific.Only seafloor spreading was the supporting evidence

The SupercontinentSupercontinent cycle

The supercontinent cycle is a prediction about how the continents will move in the future, based on how they moved in the past. Pangaea was the last existing supercontinent in earth history (300-150 Ma years ago)Panthalassa was the ocean that surrounded Pangaea.

Accretion is the increase of the size of the tectonic plate by addition of material along a convergent boundary.

Rifting is development of a rift, which is a linear zone where earths crust and lithosphere are pulled apart.

How plate movements alter climates and evolution

Climates:

More land at higher latitude…

Different ocean locations and therefore heat transport

Different global atmospheric circulation

Overland more glaciers, higher albedo and cooler temperatures

Evolution

Because there are different continents with different climates, a lot of different animals developed. It all depended on the climate. Even if it was the same animal on Pangaea, it is now transformed and has the right conditions for the climate on the continent. For example the mammoth. Because of plate movements they lives in hotter areas and lost their fur. That is what we know today as elephants.

Theory of plate tectonicsLithosphereThe lithosphere is the outer shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that is elastically on time scales of thousands of years or greater.

Asthenosphere The asthenosphere is the mechanically weak and ductilely-deforming region of the upper mantle of the Earth. It lies below the lithosphere

How plates move

Plates at our planet’s surface move because of the heat inside the Earth’s core that causes molten rock in the mantle layer to move. It moves in a pattern called a convection cell. These form when warm material rises, cools, and sinks down. As the cooled material sinks down, it is warmed and rises again.

Three types of plate boundaries

Divergent boundaries

Convergent boundaries

Transform boundaries

for explanation look at picture on the left

Isostatsy

Equilibrium in the earth's crust such that the forces tending to elevate landmasses balance the forces tending to depress landmasses.

Isostatic adjustments

The movement of the lithosphere to reach isostasy are called isostatic adjustment.

Stress

The force acting on a rock or another solid to deform it, measured in kilograms per square centimeter or pounds per square inch.When the stress is really high and strong solids may deform

Divergent Boundary

Seafloor spreadingThe force acting on a rock or another solid to deform it, measured in kilograms per square centimeter or pounds per square inch.

Mid-ocean ridgesAn example of an oceanic ridge is the Mid-Atlantic Ridge.  It is one part of a system of mid-oceanic ridges that stretches for 50,000 miles through the world's oceans.  The underwater mountains of the ridge may not be more than two miles higher than the surrounding sea floor. Mid-Atlantic Ridge

Paleomagnetismis the study of the record of the Earth's magnetic field in rocks. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. Magnetic reversalsA geomagnetic reversal is a change in the Earth's magnetic field such that the positions of magnetic north and magnetic south are interchanged Magnetic Symmetry

The ages of seafloor rocks are symmetrical, that supported the theory of seafloor spreading

Normal faults

Related landforms

Are what helped Wegener to establish his theory. He compared the landforms of the continents and found out that the east coast of south America looks like the west coast of Africa.

Convergent Boundary

Subduction zoneRegions where portions of the earth's tectonic plates are diving beneath other plates, into the earth's interior. They are defined by deep oceanic trenches, lines of volcanoes parallel to the trenches, and zones of large earthquakes that extend from the trenches landward.

Volcanoesis an opening, or rupture, in a planet's surface or crust, which allows hot magma, volcanic ash and gases to escape from the magma chamber below the surface.

Magmais a mixture of molten or semi-molten rock, volatiles and solids[1] that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles.

Arenal volcano of Costa Rica

Piping hot magma chamber

Three conditions under which lava formsTemperature of rock rises above the melting point of the minerals the rock is composed of.If enough pressure is removed from the rock the melting point will decrease and the rock will melt.The addition of fluids such as water, may decrease the melting point and cause the rock to melt.

LavaLava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites

Lava flow

Volcanocommon

locations

Convergent plateboundaries

major zone of active volcanoes encircling the pacific ocean is the ring of fireIt is the location with the most (75%) volcanic activity on earth with over 450 volcanoes

Pyroclastic materialPyroclastic material is another name for a cloud of ash, lava fragments carried through the air, and vapor. Such a flow is usually very hot, and moves rapidly. Pyroclastic flows can extend miles from the volcano, and destroy life and property within their paths.

viscosityThe resistance of a fluid to flow. Fluids with a high viscosity resist flow. Fluids with a low viscosity flow freely.

how magma contentsproduce explosiveeruptions Explosive eruptions are favored by high gas content & high viscosity magmas. The explosive bursting of bubbles fragments the magma into clots of liquid that cool as they fall through the air. These solid particles become pyroclasts or volcanic ash.

Types of volcanoComposite Volcanoes (also called strato volcanoes), Mt. St. Helens, Mt. Rainier, Pinatubo, Mt. Fuji, Merapi, Galeras, Cotopaxi Shield Volcanoes (also called shields), Kilauea and Mauna Loa Fernandina ,Karthala, Erta Ale, Tolbachik, Masaya Cinder Cones, Paricutin in Mexico. In Iceland, Surter I and Surter IISpatter Cones Isla Bartolomé, adjacent to the large island of Santiago, Galapagos IslandsComplex Volcanoes (also called compound volcanoes). McDonald Island ,Long Island ,Guntur ,Dieng ,Dukono ,Unzen ,Asama ,Iwate

ShieldShield volcanoes are huge in size.  They are built by many layers of runny lava flows. Lava spills out of a central vent or group of vents.  A broad shaped, gently sloping cone is formed.  This is caused by the very fluid, basaltic lava which can't be piled up into steep mounds.

Cinder conesA cinder cone is a steep conical hill formed above a vent.  Cinder cones are among the most common volcanic landforms found in the world.  They aren't famous as their eruptions usually don't cause any loss of life.  Cinder cones are chiefly formed by Strombolian eruptions.  The cones usually grow up in groups and they often occur on the flanks of strato volcanoes and shield volcanoes.

Composite volcanoesComposite volcanoes, also called strato volcanoes, are formed by alternating layers of lava and rock fragments.  This is the reason they are called composite.      Strato-volcanoes often form impressive, snow-capped peaks which are often exceeding 2500m in height, 1000sq.km in surface, and 400km3 in volume.      Between eruptions they are often so quiet they seem extinct.  To witness the start of a great eruption requires luck or very careful surveillance.

Caldera A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption. They are sometimes confused with volcanic craters. The word comes from Spanish caldera, and this from Latin CALDARIA, meaning "cooking pot".

Islands close to new zealand

Continental+oceanic crust

When an oceanic plate pushes into and subducts under a continental plate, the overriding continental plate is lifted up and a mountain range is created.This can cause volcanism and mountain chainsFor example islands near new Zealand

Oceanic+ oceanic

When two oceanic plates converge one is usually subducted under the other and in the process a deep oceanic trench is formed. The Marianas Trench, for example, is a deep trench created as the result of the Phillipine Plate subducting under the Pacific Plate.

Marianas trench

Collision zoneA collision zone occurs when tectonic plates meeting at a convergent boundary both bear continental lithosphere. As continental lithosphere is usually not subducted due to its relative low density, the result is a complex area of orogeny involving folding and thrust faulting as the blocks of continental crust pile up above the subduction zone.

Examples:Philippine Mobile BeltMolucca Sea Collision ZoneCarlin Unconformity

Continental+continental crustWhen two continents meet head-on, neither is subducted because the continental rocks are relatively light and, like two colliding icebergs, resist downward motion. Instead, the crust tends to buckle and be pushed upward or sideways. The collision of India into Asia 50 million years ago caused the Eurasian Plate to crumple up and override the Indian Plate. After the collision, the slow continuous convergence of the two plates over millions of years pushed up the Himalayas and the Tibetan Plateau to their present heights. Most of this growth occurred during the past 10 million years. Compression and uplift….landforms produced

Transform boundaryReverse faultsAlong a reverse fault one rocky block is pushed up relative to rock on the

other side. For example the Sierra

madre, California

Strike-slip faultsStrike-slip faults have a different type of movement than normal and reverse faults. You probably noticed that the blocks that move on either side of a reverse or normal fault slide up or down along a dipping fault surface.The rocky blocks on either side of strike-slip faults, on the other hand, scrape along side-by-side. You can see in the illustration that the movement is horizontal and the rock layers beneath the surface haven't been moved up or down on either side of the fault. For example the san andreas fault.

TensionStress that stretches or extends rocks, so that they become thinner vertically and longer laterally. Tension may be caused by divergence or rifting.Shear stressShear stress is the stress component parallel to a given surface, such as a fault plane, that results from forces applied parallel to the surface or from remote forces transmitted through the surrounding rock.Related landformsFault block mountains are very large blocks of rock, sometimes hundreds of kilometers in extent, created by tectonic and localized stresses in the Earth's crust. A Graben is a depressed block of land bordered by parallel faults. Graben is German for ditch or trench.

Other related landforms

Dome mountainsThese mountains are the result of a great amount of melted rock pushing its way up under the earth. Over thousands of years the dome mountains form in the place where the earth is pushed up.Hot spotsThe places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries.

Yosemite national park

Most fam

ous hotspot on earth…

the H

awaiian

islands

Earthquakes

Elastic reboundDescribes how energy is spread during an earthquake. Rocks on opposite sides of a fault and suffer under force and shift so that they deform. Than a sudden movement occurs along the fault and the released energy lets the rocks break and snap back to their original form

SeismologyIs the study of earthquakes and different waves that run through the earth or other planets. Also included are the effects of earthquakes, like for example tsunamis Seismograph Is an instrument used to measure and record ground motion.

FocusIt is the point under the earth surface where the seismic come from while an earthquake

Epicenter

Is the location on the earth’s surface directly above the focus. This is the location on the surface where the seismic energy is the biggest.

Seismic waves Seismic waves are produced by the energy released by earthquakes; the waves radiate from the quake’s epicenterBody wavesA body wave is a seismic wave that moves through the interior of the earth, as opposed to surface waves that travel near the earth's surface. P and S waves are body waves. Each type of wave shakes the ground in different ways.

P wavesis a seismic body wave that shakes the ground back and forth in the same direction and the opposite direction as the direction the wave is moving.

S waves is a seismic body wave that shakes the ground back and forth perpendicular to the direction the wave is moving. 

Surface wavesis a seismic seismic wave that is trapped near the surface of the earth.

How seismic waves led to determination of earth’s interior

S waves can only go through solidsP waves can go through all states of matter And because you don’t have any seismic energy on the other side of the earth during an earthquake, it means that there is a core and you can also say where the earth is liquid and where it is solid

Earthquakes not resulting from movement along plate boundaries Are also called intraplate earthquakes. Other than interplate earthquakes they occur in a tectonic plate and not between them. Even today scientists cannot explain why these occur. One of the biggest problems is that they are not predictbale because we don’t know anything about them.

Earthquake in china

Magnitude

 A measure of the amount of energy released by an earthquake, as indicated on the Richter Scale.

Intensity

The intensity of an earthquake at a particular locality indicates the violence of earth motion produced there by the earthquake. It is determined from reported effects of the tremor on human beings, furniture, buildings, geological structure, etc. 

Mercalli scaleThe Mercalli intensity scale is a seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake, and is distinct from the moment magnitude   usually reported for an earthquake (sometimes described as the obsolete Richter magnitude), which is a measure of the energy released. The intensity of an earthquake is not totally determined by its magnitude.

Tsunami

is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions(including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami