The Earth’s Moving Plates Earth Science The Earth’s Moving Plates

Plate Boundaries The movement of the tectonic plates causes both sudden and gradual changes to the Earth’s surface These changes are related to the three types of plate boundary: Convergent Divergent Transform fault

Divergent Boundaries The spot where two plates are being pulled apart is called a divergent boundaries The separation of two plates allows magma to rise to the surface and create new crust Ex. Sea Floor Spreading

Divergent Boundaries The surface of the Earth is changed because the lava can create cones rising up to a kilometer above the ocean floor This creates the mid-ocean ridges

Divergent Boundaries On land divergent boundaries create rift valleys Iceland is being split by a the diverging of the North American and Eurasian plates The Saudi Arabian plate and African plate are also diverging

Convergent Boundaries Since new crust is formed at divergent boundaries, and since the Earth isn’t growing, old crust must be getting destroyed This destruction happens at convergent boundaries

Convergent Boundaries One plate sinks under another plate at the convergent boundary This sinking is the subduction zone There are 3 convergent boundaries: Continental Oceanic Oceanic oceanic Continental Continental

Continental-Oceanic Convergence 2 land forms are created at the boundaries: Mountains Ocean trenches Mountains = the crust raised up much higher that that surrounding it Trenches are steep depressions along the edge of continents

Oceanic-Oceanic Convergence One oceanic plate will be subducted under the other This forms trenches Challenger Deep formed at the Pacific and Philippine plate boundary (11000m) is the deepest trench Volcanic activity also gives rise to volcanic islands

Continent-Continent Convergence There is no subduction zone when continents converge 2 land forms are created: Mountains Plateaus Plateaus are areas of high level ground

Transform Fault Boundaries Discovered by a Canadian Scientist, J Tuzo Wilson , while using paper to model faults They are areas where convergent or divergent boundaries transform (change) into a fault

Transform Fault Boundaries A fault is an area where rock is being broken by plate movement Plates slide along each other in opposite directions at transform fault boundaries

Transform Fault Boundaries These boundaries are mostly in the ocean The San Andreas fault is a famous terrestrial fault W. California on the Pacific Plate moves north past E. California on the N. A. plate These boundaries cause many shallow earthquakes

Review of Plate Boundaries There are 3 kinds of plate boundaries: Convergent Divergent Transform Fault Plate boundaries change the Earth’s crust Ocean trenches and rift valleys Mountain building Plateaus The plate boundaries also create earthquakes and volcanoes

Earthquakes How Earthquakes Happen Earth Science Earthquakes How Earthquakes Happen

Effects of Plate Movement Earthquakes result from plate movement Because plates are not smooth they lock together Pressure builds up at the lock until the plates suddenly move The energy released by the movement causes vibrations that move through the crust Earthquake animation

Earthquakes The vibrations are called earthquakes Earthquakes occur at convergent, divergent, and transform fault boundaries IRIS Seismic Monitor Canadian Earthquakes

Divergent Boundary Earthquakes The quakes occur when the pressure of magma pushing upward is great enough to split the crust above it These quakes are small, local and constant along the Atlantic mid ocean ridge

Convergent Boundary Earthquakes At subduction zones, the bottom plate gets stuck on the top plate When the stuck spot breaks free the top plate moves causing a large earthquake The longer the stick, the greater the quake

Convergent Quakes in BC Southern BC has ~200 quakes a year as the North American plate subducts the Juan de Fuca plate

Transform Fault Boundary Earthquakes Plates moving past each other in opposite directions can also get stuck Like a convergent earthquake the longer it takes before the plates unstick the stronger the quake

Transform Fault Boundary Earthquakes Many strong quakes occur along the San Andrea-North American fault

Effects of Earthquakes Earthquakes can cause dramatic damage The damage occurs due to seismic waves Earthquakes often happen deep in the crust The spot the earthquake occurs is the focus Residential damage in Prince William Sound, Alaska, due to liquefaction caused by a 1964 9.2-magnitude earthquake.

Effects of Earthquakes The spot on land over the earthquake is the epicenter Seismic waves are shock waves that move off in all directions from the focus

Effects of Earthquakes There are 2 main types of seismic waves: P waves- primary waves (compress) S waves- secondary waves (sheer)

Seismic Waves Both S waves P waves Originate from the same focus Travels through liquids and solids Push and pull material as they move Travel ~8 km/s Cause the first movement felt in a quake Both Originate from the same focus Begin at the same time Can be felt at the Earth’s surface S waves Travel through solids only Make the rocks vibrate up, down, or sideways Travel ~4.5km/s Usually cause more building damage

Damage from Earthquakes Earthquakes damage human structures: Buildings Roads Tunnels and overpasses Water lines Fuel lines and tanks Fires, lack of water and being crushed all endanger people

Tsunamis Tsunamis are another danger of earthquakes Tsunamis are series of ocean waves created by the quake The are small in the open ocean but travel at up to 800 km/h They slow as they approach shore, but rise to heights of up to 30m

- often form from the friction between moving tectonic plates. Earthquakes - often form from the friction between moving tectonic plates. This accounts for 95 % of all earthquakes. The Juan de Fuca convergent plate boundary west of Vancouver Island has many earthquakes. Large earthquakes hit this region every 200 - 800 years. Transform boundary San Andreas fault

Describing Earthquakes Scientists understand why they happen, but it is very difficult to predict their timing, exact location, and strength. Their pressure build-up happens underground, over very long periods of time. The focus of the earthquake is where the pressure is finally released. The epicentre is the point on the surface directly above the focus.

Release of energy starts here...

Earthquakes occur at various depths, depending on the plates involved. Depth of Earthquakes Earthquakes occur at various depths, depending on the plates involved. Earthquakes at the surface tend to cause more damage. See page 528

Earthquake Magnitude Scale Earthquake Effects Estimated Number Each Year 2.5 or less Usually not felt, but can be recorded by seismograph. 900,000 2.5 to 5.4 Often felt, but only causes minor damage. 30,000 5.5 to 6.0 Slight damage to buildings and other structures. 500 6.1 to 6.9 May cause a lot of damage in very populated areas. 100 7.0 to 7.9 Major earthquake. Serious damage. 20 8.0 or greater Great earthquake. Can totally destroy communities near the epicenter. One every 5 to 10 years

Earthquake Waves Earthquakes produce seismic waves. Seismology is the study of these waves. These waves reveal the source and strength of an earthquake. They also help us learn about the composition and distances of the Earth’s interior.

Earthquake Waves Types of earthquake waves: See page 529

Seismic Waves Seismic waves behave differently in different Earth layers. Knowing this, scientists can learn about earthquakes and Earth’s interior. Seismometers are used to measure seismic wave energy. Early seismometers just measured whether the ground shook. Some seismometers measure horizontal movement, others vertical movement.

Seismograms A seismogram is produced, showing when an earthquake started, how long it lasted, and the magnitude. 1 increase in magnitude = 10X stronger A magnitude 6 earthquake is 100X more powerful than a 4. Since seismic waves travel at different speeds, a distance-time graph can reveal the focus.

Review of Earthquakes Earthquakes occur at all 3 types of plate boundaries Earthquakes result from the release of pressure built up due to plates sticking together The energy released creates two types of seismic waves: P and S Earthquakes cause massive damage

Earth Science 7 Volcanoes

Volcanoes One of the effects of moving plates are volcanoes Volcanoes are openings in the earth’s crust that allow magma and other materials to come through

Plates and Volcanoes The location of a volcano affects the behavior and composition of the volcano Three locations volcanoes occur are: At divergent boundaries At convergent boundaries At hot spots

Volcanoes at Divergent Boundaries Magma pushes plates apart and moves to the surface here 75% of lava is produced at these boundaries Lava hardens quickly in the water and builds undersea mountains and islands

Volcanoes at Divergent Boundaries The youngest volcanoes in BC are on Mt. Edna, Hoodoo Mount, Lava Fork, and Crow Lagoon Stikine Volcanic Belt They are on a divergent boundary in the North West corner of BC near Alaska It has been 150 years since any of them erupted

Volcanoes at Convergent Boundaries The magma at convergent boundaries is thicker than at divergent boundaries Gases cannot escape until tremendous pressure builds up causing explosive release Gases, lava and ash are all blasted out of the volcanoes by the force

Volcanoes at Convergent Boundaries The last explosive eruption in BC occurred at Mt. Meager near Whistler 2350 years ago (long, long ago)

Hot Spot Volcanoes These volcanoes are the exceptions to activity along plate boundaries Hot spots are areas where the mantle temperature is higher than normal

Hot Spot Volcanoes Large pools of magma collect at hot spots The magma melts the overlying rock and lava pours out The lava is runny so gases escape easily and eruptions are rarely explosive

Hot Spot Volcanoes When these volcanoes are in the ocean the lava quickly hardens into a steep cone The cone may rise to form an island; This is the way the Hawaiian islands formed

Hot Spot Volcanoes There is a hot spot in British Columbia! The Anahim Volcanic Belt stretches from Quesnel to the west coast http://gsc.nrcan.gc.ca /volcanoes/map/inde x_e.php

Volcano Composition Volcanoes can also be classified by their composition Cinder cone volcanoes- smallest of the three volcanoes Cone has steep sides Bowl shaped cone at the top Built from layers of ash and volcanic rock They erupt violently

Volcano Composition Shield volcanoes are the largest of the 3 types of volcanoes They are made of cooled lava The cones have gently sloping sides These form at hot spots and divergent boundaries They erupt quietly

Volcano Composition Composite(strato) volcanoes are a mix of the other two volcanoes They are made of alternating layers of lava and ash They may erupt violently or quietly

Volcanoes The movement of tectonic plates causes volcano formation. Composite volcanoes – found along plate boundaries Layers of ash and thick lava form a tall cone. As magma reaches the surface, it cools, hardens, and traps gases below. Pressure builds; eventually, there is an eruption. See pages 532 - 534 Mount St. Helens is a composite volcano.

Mt St Helen’s, Washington

2. Shield Volcanoes 3. Rift Eruptions – these are not found at plate boundaries but instead form over hot spots. Thin magma/lava flows out from a hot spot and forms a low, wide cone. The Hawaiian Islands are an example of a chain of shield volcanoes 3. Rift Eruptions – occur along long cracks in the lithosphere These are not explosive, but they release massive amounts of lava.

Shaped like a “soldier’s shield” lying down

Occur when magma erupts through long cracks in lithosphere Occur when magma erupts through long cracks in lithosphere. Curtain-like fountains of lava erupt at spreading ocean ridges or rifts in continental crust. Can release enormous amounts of lava. Take the Section 12.2 Quiz

The Effects of Volcanoes Volcanoes effect the environment Some effects are destructive, and some are beneficial

The Destructive Effects of Volcanoes Volcanic ash in the atmosphere clouds the amount and reduces Earth’s temperature Buries the surrounding area in 10s of meters of mud and ash flows of mud, and lava can destroy stationary objects in their path Pyroclastic flows (hot clouds) cook and suffocate living things

The Beneficial Effects of Volcanoes The beneficial effects of volcanoes are: Ash improves soil Diamonds form in volcanic rock Obsidian is formed from lava Obsidian is used for scalpels in eye surgery today, and was important in aboriginal tool making.

Review of Volcanoes Volcanoes change the Earth’s crust Volcanoes form at different locations Divergent boundaries Convergent boundaries Hot spots Volcanoes have destructive and beneficial effects