Plate tectonics

Do now 1. Identify each boundary 2. What landform is made from each boundary? Convergent Boundary _________________________ Divergent Boundary __________________________ Transform Boundary__________________________ Divergent boundary Example is the Mid-Atlantic Ridge--this is a mostly underwater mountain range that runs through the Arctic and Atlantic Oceans. 3. Using the image to the right, label the parts of the Earth’s layers. E)____________________ G)_______________________ F)____________________ H)_______________________

Exit Ticket True or False. The inner core of the earth is what causes the plates to be able to move List the 3 different types of convergent boundaries. Provide an example or landform of each What is an ocean trench?

Review: PLATE BOUNDARIES Plate Boundaries--The location were two plates meet. Divergent boundaries -- where new crust is generated as the plates pull away from each other. Convergent boundaries -- where crust is destroyed as one plate dives under another. Transform boundaries -- where crust is neither produced nor destroyed as the plates slide horizontally past each other. In plate tectonics, a divergent boundary is a linear feature that exists between two tectonic plates that are moving away from each other. These areas can form in the middle of continents or on the ocean floor. As the plates pull apart, hot molten material can rise up this newly formed pathway to the surface - causing volcanic activity. Where a divergent boundary forms on a continent it is called a RIFT or CONTINENTAL RIFT, e.g. African Rift Valley. Where a divergent boundary forms under the ocean it is called an OCEAN RIDGE. Convergent boundaries are where the plates move towards each other. There are three types of convergent boundary, each defined by what type of crust (continental or oceanic) is coming together. Therefore we can have: continent-continent collision, continent-oceanic crust collision or ocean-ocean collision. The third type of boundary are transform boundaries, along which plates slide past each other. The San Andreas fault, adjacent to which the US city of San Francisco is built is an example of a transform boundary between the Pacific plate and the North American plate.

Oceanic-Oceanic Convergence Oceanic-continental convergence Oceanic-Oceanic Convergence Continental-Continental convergence. Oceanic-continental convergence--Where the plate that is covered by water and the plate that is covered by land meet. Oceanic-Oceanic Convergence--when two oceanic plates converge, one is usually sub ducted under the other, and in the process a trench is formed Continental-Continental convergence-- When two continents meet head-on, neither is sub ducted 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

Oceanic-Continental Convergence -Trenches are created by subduction -One plate is being subducted under another Oceanic- Oceanic Convergence -A trench is formed when one plate is subducted and two oceanic plates converge. -One example is Marianas Trench Continental-Continental Convergences -Powerful collision -Because the density of the plates is lower than the mantle, subduction is prevented. A mountain is formed because subduction is difficult Convergent Boundaries -the location where sinking of a plate occurs is called a subduction zone -Convergence is a very slow collision of plates -There is three types of convergent boundaries -Formed where fast Pacific Plate converges against the slower Philippine Plate -This convergence results in volcanoes. -Many volcanoes (like Hawaii) are situated on island arcs that are really trenches that was created by convergences! Continental-Continental Convergences - Himalayan Mountain is formed by the Eurasian Plate overriding the Indian Plate 50 million years ago! -Mountain ranges like the Alps and the Rockies were formed this way.

REAL LIFE APPLICATIONS Plate movement cause a lot of natural disasters Plate movement can cause large cracks in the surface, earthquakes, and fissures Plate also create mountains by pushing up on each other. Volcanoes can erupt from plate movement Geodesy is the study of the size and shape of earth People study plate boundaries with geodesy Scientist can study plate boundaries on the ground but the best way is through a satellite.

Exit Ticket True or False. The inner core of the earth is what causes the plates to be able to move List the 3 different types of convergent boundaries. Provide an example or landform of each What is an ocean trench?

Volcanoes are formed by: - Subduction - Rifting - Hotspots Volcanoes can be formed in three ways: Via subduction. The subducting slab dehydrates to form new melt that will rise through the crust to be erupted at the surface. Via rifting. When two plates pull apart magma rises, producing volcanic eruptions at the surface. At “Hotspots”….hotspot do not necessarily occur along a plate boundary. So hotspot volcanoes can form in the middle of tectonic plates….Click for example. Subduction Rifting Hotspots

Pacific Ring of Fire Hotspot volcanoes Hotspot volcanoes in the middle of the Pacific plate. Can anyone guess where they are? Answer: Hawaii

What are Hotspot Volcanoes? A hotspot is a location on the Earth's surface that has experienced active volcanism for a long period of time. Firstly, what are hotspot volcanoes and how do they form? A hotspot is a location on the Earth's surface that has experienced active volcanism for a long period of time. The source of this volcanism is a mantle plume of hot mantle material rising up from near the core-mantle boundary through the crust to the surface (see left diagram). A mantle plume may rise at any location in the mantle, and this is why hotspot volcanoes are independent from tectonic plate boundaries. The Hawaiian island chain are an example of hotspot volcanoes (see right photograph). The Hawaiian island chain are examples of hotspot volcanoes.

The tectonic plate moves over a fixed hotspot forming a chain of volcanoes. Hotspot’s commonly form volcanic island chains (like the Hawaiian islands). These result from the slow movement of a tectonic plate over a FIXED hotspot. Persistent volcanic activity at a hotspot will create new islands as the plate moves the position of the “old” volcanic island from over the hotspot. Therefore at one end of the island chain you see the youngest, most active volcanic islands (directly over the hotspot) and along the island chain the extinct volcanoes become older and more eroded (see diagram). This way geologists can use hotspot volcano chains to track the movement of the tectonic plate through time. Hotspot’s commonly form volcanic island chains (like the Hawaiian islands) These result from the slow movement of a tectonic plate over a FIXED hotspot

…what’s the connection? Earthquakes and Plate Tectonics… …what’s the connection? We have seen the connection between volcanoes and plate tectonics. Is there a connection between earthquakes and plate tectonics?

As with volcanoes, earthquakes are not randomly distributed over the globe At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur. Figure showing the distribution of earthquakes around the globe The black dots on this map of the world depict where earthquake activity is occurring. You can see that, as with volcanoes, the earthquakes are NOT randomly distributed around the globe. Instead they occur in linear patterns associated with plate boundaries. (Note this diagram of earthquake distribution closely resembles the Pacific Ring of Fire distribution of volcanism).

Occur when rocks under stress shift suddenly along a fault. What’s an Earthquake? Earthquakes are movements of the ground that are caused by a sudden release of energy when along a fault move. Occur when rocks under stress shift suddenly along a fault. A fault is a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture. Stress is a force that can change the size & shape of rocks.

Anatomy of an Earthquake Focus --- The area along the fault where slippage first occurs. Epicenter – The point on the Earth’s surface directly above the focus. 2 main types of seismic waves: Body waves – travel through the body of a medium. Surface waves – travel along the surface of a body rather than through the middle.

Types of Body Waves Primary waves or P waves – move the fastest; first to be recorded; can travel through solids and liquids; cause rock particles to move together and apart along the direction of waves. Secondary waves or S waves --- second to be recorded; only travel through solids; cause rock particles to move at right angles to the direction in which waves are traveling. Cause the greatest damage.

2 Types of Surface Waves Surface waves or Love waves or L waves – cause rock to move side to side & Perpendicular to direction waves are traveling. Rayleigh waves -- cause the ground to move with an elliptical, rolling motion.

Recording Earthquakes Seismograph – records & detects vibrations in the ground. Consists of 3 separate devices: One device records the vertical motion of the ground. The other 2 devices record horizontal motion in the east-west and north-south. The seismograph records motion by tracing wave-shaped lines on paper and translating the motion into electronic signals (known as a seismogram).

Measuring an Earthquake Richter scale – measures the ground motion from an earthquake to find its strength. Moment magnitude is a measurement of a quakes strength based on size of area the fault moves, the average distance that the fault blocks move, and the rigidity of the rocks in the fault zone. Mercalli scale – expresses the intensity of an earthquake or the amount of damage it causes. Expressed by a roman numeral and a description.

Where do earthquakes form? We know there are three types of plate boundaries: Divergent, Convergent and Transform. Movement and slipping along each of these types of boundaries can form an earthquake. Depending on the type of movement, the earthquakes occur in either a shallow or deep level in the crust. The majority of tectonic earthquakes originate at depths not exceeding tens of kilometers. In subduction zones, where old and cold oceanic crust descends beneath another tectonic plate, “Deep Focus Earthquakes” may occur at much greater depths (up to seven hundred kilometers!). These earthquakes occur at a depth at which the subducted crust should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep focus earthquakes is faulting. Earthquakes may also occur in volcanic regions and are caused there both by tectonic faults and by the movement of magma (hot molten rock) within the volcano. Such earthquakes can be an early warning of volcanic eruptions. Figure showing the tectonic setting of earthquakes

Plate Tectonics Summary The Earth is made up of 3 main layers (core, mantle, crust) On the surface of the Earth are tectonic plates that slowly move around the globe Plates are made of crust and upper mantle (lithosphere) There are 2 types of plate There are 3 types of plate boundaries Volcanoes and Earthquakes are closely linked to the margins of the tectonic plates The take home messages from this lecture: See if the students remember what each layer, type of plate and type of boundary are called. Can they describe the motion of the three plate boundary types? Where does volcanism occur in relation to plate tectonics? Where do earthquakes occur in relation to plate tectonics?

Exit ticket Describe the motion of the three plate boundary types? Where does volcanism occur in relation to plate tectonics? Where do earthquakes occur in relation to plate tectonics?