EARTH S PROCESSES VOCABULARY Divergent Convergent Subduction Transform Ring of Fire Earthquake Stress Strain Fault Primary Waves Secondary Waves Surface Waves Focus Epicenter Seismology Magnitude Richter Scale Modified Mercalli Scale Pancaking Tsunami Seismic Belt Seismic Gaps
EARTH S PROCESSES Plate Tectonics, Earthquakes, Volcanoes
THE THEORY OF PLATE TECTONICS Theory of Plate Tectonics- Earth s crust and rigid upper mantle are broken into enormous slabs called plates These tectonic plates move in different directions and at different rates over Earth s surface
HOW/ WHY DO PLATES MOVE? Convection Convection in the mantle causes a circulation of molten material. This circulation moves the tectonic plates around on the surface Ridge Push Ridges (mountain areas) are higher in elevation than the surrounding area. Here, magma is pushing up moving the plates apart Gravity pull Plates are pulled down by gravity back into the mantle
BOUNDARIES Tectonic plates interact at plate boundaries. There are 3 major types you are responsible for: Divergent Convergent Transform
DIVERGENT BOUNDARIES At divergent boundaries, two tectonic plates are moving apart This happens on the seafloor- mostly at ocean ridges This results in the formation of new ocean crust This rarely happens on land, but this is what a rift valley is East Africa This results in the formation of new continental crust
CONVERGENT BOUNDARIES At convergent boundaries, two tectonic plates move towards one another. *There are three types depending on the type of crust involved.
OCEANIC-OCEANIC BOUNDARIES Subduction occurs One plate (more dense) will descend beneath the other plate This creates a deep sea trench The crust that was subducted goes back into the mantle and is recycled as magma. Some of the magma that forms is forced back to the surface, erupts, and forms an arc of volcanic islands Ex) Aleutian Islands- Alaska
OCEANIC-CONTINENTAL BOUNDARY Subduction occurs Oceanic crust is subducted beneath the continental crust, because it is more dense. Here, a series of volcanoes erupt along the edge of the continental plate Ex) Andes Mountains- South America
CONTINENTAL-CONTINENTAL BOUNDARY Subduction cannot occur, because both continental crusts have the same density When these plates collide, the edges become crumpled, and they uplift to form mountain ranges Ex) the Himalayas in Asia
TRANSFORM BOUNDARIES At transform (strike-slip) boundaries, two plates slide horizontally past one another No new crust is created The existing crust is fractured or deformed Ex) the San Andreas Fault- California
MAGMA All volcanoes are fueled by magma deep beneath the Earth s surface. Magma forms when temperatures are hot enough to melt the rock This occurs in the base of the lithosphere and in the asthenosphere
VOLCANOES Magma chambers deep within the earth fuel volcanoes Once magma reaches the surface, it is called lava.
3 TYPES OF VOLCANOES Shield - Cinder-cone Composite
SHIELD VOLCANOES A shield volcano is a mountain with gently sloping sides and a circular base Shield volcanoes are formed from layers upon layers of basaltic lava accumulating during non-explosive reactions
CINDER-CONE VOLCANOES With cinder-cone volcanoes, material ejected into the atmosphere falls back onto the earth and piles around the vent of the volcano. Cinder-cones have steep sides and they are more explosive due to gas pockets in lava
COMPOSITE VOLCANOES In composite volcanoes, layers of volcanic fragments alternate with lava They are violently explosive and most dangerous to humans. They are also the largest volcanoes. Mount St. Helens in Washington State is a composite volcano.
DANGERS WITH VOLCANOES Lava Flows are an obvious danger, but there are other dangers related to volcanoes Tephra- rock fragments that are thrown into the air during an eruption These can be pieces of the volcanic cone or newly cooled lava Pyroclastic flows- clouds of gas, ash, and tephra that are expelled during violent eruptions These can move very fast uprooting trees and demolishing houses.
PYROCLASTIC FLOWS
WHERE CAN YOU FIND VOLCANOES? Most volcanoes are located near plate boundaries The most popular is the Pacific plate boundary called the Ring of Fire
SAFETY TIPS Stay away from active volcanoes. If you live near an active volcano, keep goggles and a mask in an emergency kit, along with a flashlight and a working, battery-operated radio. Know your evacuation route. Keep gas in your car.
DURING AN ERUPTION Evacuate only as recommended by authorities to stay clear of lava, mud flows, and flying rocks and debris. Avoid river areas and low-lying regions. Before you leave the house, change into long-sleeved shirts and long pants and use goggles or eyeglasses, not contacts. Wear an emergency mask or hold a damp cloth over your face. If you are not evacuating, close windows and doors and block chimneys and other vents, to prevent ash from coming into the house. Be aware that ash may put excess weight on your roof and need to be swept away. Wear protection during cleanups. Ash can damage engines and metal parts, so avoid driving. If you must drive, stay below 35 miles (56 kilometers) an hour.
EARTHQUAKES Chapter 19
Earthquakes are natural vibrations of the ground cause by movement along gigantic fractures in Earth s crust, or sometimes, by volcanic eruptions Earthquakes occur when rocks fracture deep within the Earth Fractures are caused by stress Stress- forces per unit area acting on a material exceeds the strength of the rock involved
3 KINDS OF STRESS Tension- Stress that pulls a material apart Compression- stress that decreases the volume of a material Shear- stress that causes a material to twist Strain is the deformation of materials in response to stress
FAULTS A fault is a fracture along rock where movement takes place Fault plane is the surface along which the movement takes place.
TYPES OF FAULTS Normal- fractures caused by horizontal tension This fault extends the crust Hanging wall goes below foot wall Reverse- faults formed by horizontal compression Hanging wall will go above foot wall Strike-slip- fractures caused by horizontal shear Rocks move to one side
EARTHQUAKE WAVES Most earthquakes are caused by movement along faults An earthquake occurs from the release of stress that builds if the plates(rocks) snag and cannot slide past one another Seismic waves are the vibrations of the ground during an earthquake
3 TYPES OF SEISMIC WAVES Primary(P-waves)- squeeze and pull rocks in the same direction along the direction the wave is travelling( back and forth motion) Secondary (S-waves)- rocks move at right angles in relation to the direction of the wave (up and down or side to side) Surface waves(l-waves)- move in two directions as they pass through rock (up, down, left, and right)
WHERE DO WAVES MOVE? Surface waves move along the Earth s surface P-waves and S-waves are body waves Body waves move through the interior of the Earth from the focus Focus is the origination of an earthquake-the point of failure of the rocks Epicenter- point on the Earth s surface that is directly above the focus
SEISMOMETERS AND SEISMOGRAPHS Seismology- the study of earthquake waves During an earthquake, the entire globe is shaken. Humans may not feel these vibrations, but there are instruments that can detect waves traveling through the Earth. Seismometer- instrument that can detect waves traveling through the Earth Seismogram- record of waves detected by a seismometer
TRAVEL TIME During an earthquake, p-waves will arrive first to a seismic facility Seismologists can use the difference in the wave arrival times to determine their distance from the epicenter of an earthquake
CLUES TO EARTH S INTERIOR The study of seismic waves allows us to understand the composition of the Earth S-waves cannot travel through liquid, so they are not seen past the inner core P-waves are refracted in liquids, this leaves a zone on the Earth that no p-waves are seen
MEASURING EARTHQUAKES How many earthquakes occur a year? There are over 1 million earthquakes a year 90% of earthquakes are never felt and they do no damage
Magnitude- measure of the amount of energy released during an earthquake Richter scale- numerical scale based on the size of seismic waves from an earthquake Each number increases the waves by a factor of 10 Ex) magnitude of 8 is 10 x magnitude 7
MOMENT MAGNITUDE SCALE Scale that factors in size of fault rupture, amount of movement, and rock s stiffness Estimated by size of several times of seismic waves
MODIFIED MERCALLI SCALE Rate based upon types of damage and other effects of an earthquake during and after occurrence This measures the amount of damage done
DEPTH OF FOCUS The depth of a focus is described as: Shallow Intermediate Deep **Shallow earthquakes have a higher intensity, because greater vibrations are produced**
LOCATING AND EARTHQUAKE One seismic facility cannot determine the location of an earthquake A seismic facility can determine the distance from an epicenter, but not the direction It takes a minimum of 3 stations to locate an epicenter The more stations used, the more accurate the location
EARTHQUAKES AND SOCIETY Most damage from earthquakes is a result of the prolonged shaking of the ground surface Buildings collapse, because they cannot withstand the stress. This is what causes most earthquake deaths. There can be aftershocks days after the initial quake
EARTHQUAKE HAZARDS Structural Failure Most buildings are not built to withstand violent vibrations The ground floor will fail causing the rest of the building to fall onto this layer This is called pancaking Height of buildings Earthquakes have a harder time making tall buildings sway This is why an earthquake can knock over a 4 story building and leave a 15 story building standing
Land and Soil failure In sloping areas, earthquakes can cause landslides Fluid-saturated sand can undergo liquefaction through vibrations- this acts like quicksand Soft soils also intensify vibrations causing more damage
TSUNAMI Tsunami is a large ocean wave generated by vertical motions on the seafloor during an earthquake A 1 meter wave in the ocean can be a 30 meter wave in shallow water near the coast
SEISMIC RISK Most earthquakes occur in areas called seismic belts These are places where future earthquakes are probable Areas that have suffered earthquakes in the past have a probability of future earthquakes
EARTHQUAKE PREDICTION Seismologists study the history of earthquakes in an area and the rate at which strain builds up in the rocks to predict earthquakes Seismic gaps- sections of active faults that have not experienced significant earthquakes for a long period of time
EARTHQUAKE SAFETY Have an earthquake readiness plan. Consult a professional to learn how to make your home sturdier, such as bolting bookcases to wall studs, installing strong latches on cupboards, and strapping the water heater to wall studs. Locate a place in each room of the house that you can go to in case of an earthquake. It should be a spot where nothing is likely to fall on you. Keep a supply of canned food, an up-to-date first aid kit, 3 gallons (11.4 liters) of water per person, dust masks and goggles, and a working batteryoperated radio and flashlights. Know how to turn off your gas and water mains.
DURING AN EARTHQUAKE Drop down; take cover under a desk or table and hold on. Stay indoors until the shaking stops and you're sure it's safe to exit. Stay away from bookcases or furniture that can fall on you. Stay away from windows. In a high-rise building, expect the fire alarms and sprinklers to go off during a quake. If you are in bed, hold on and stay there, protecting your head with a pillow. If you are outdoors, find a clear spot away from buildings, trees, and power lines. Drop to the ground. If you are in a car, slow down and drive to a clear place. Stay in the car until the shaking stops.