EARTHQUAKES & VOLCANOES

EFFECTS OF PLATE TECTONICS  When plates move, they bump into each other  Depending on the type of plate boundary, different deformations result  Two special events/formations happen as well:  Earthquakes  Volcanoes

EARTHQUAKES  Earthquake: shaking of the ground that results from the movement of rock beneath Earth’s surface  Stress on rocks from pushing/pulling changes its shape/volume of the rock  Types of Stress:  Shearing – causes rocks to slip  Tension – stretches rock  Compression – pushes rocks together

FAULTS  Fault: a break in Earth’s crust where slabs of crust slip past each other.  Rocks on both sides of a fault can move up or down or sideways  Usually occur along plate boundaries, where the forces of plate motion compress, pull or shear the crust so much that it breaks.

TYPES OF FAULTS  Strike-Slip Faults: where rocks on either side of the fault slip past each other sideways with little up or down motion  Occurs at transform plate boundaries  Ex: San Andreas Fault, California

 Normal Faults: a fault at an angle so one block of rock lies above the fault and the other block of rock lies below the fault, caused by tension  Occurs where plates diverge  Hanging wall – half that lies above  Footwall – half that lies below

TYPES OF FAULTS  Reverse Faults: have the same structure as a normal fault, but the blocks move in the opposite direction (toward each other)  Produced by compression forces  Ex: produced part of the Appalachian Mountains in the eastern US

FRICTION ALONG FAULTS  Friction is the force that opposes motion between surfaces  When friction along a fault is low, the rocks pass easily without sticking  When friction along a fault is high, the rocks lock together and do not move.  Energy continues to build until it’s strong enough to overcome friction.  When they jerk free, you get an earthquake

 The strength of the quake depends on the amount of energy built up (how much friction there was)

MEASURING EARTHQUAKES  Two things we need to know when earthquakes happen:  Where they’re located  How “big” they were

EARTHQUAKE LOCATION  Focus – the point beneath the Earth’s surface where stressed rock breaks  Epicenter – the point on the surface directly above the focus  Found by measuring the difference between arrival times of P and S waves.

EARTHQUAKE STRENGTH  Earthquakes produce vibrations called waves, which carry energy as they travel through solid material  Seismic Waves– vibrations that carry the energy of an earthquake away from the focus, through Earths’ interior, and across the surface

TYPES OF SEISMIC WAVES  Primary Waves (P Waves) – first waves to arrive; compress and expand the ground like an accordion  Move through solids & liquids

 Secondary Waves (S Waves) – come after P waves; vibrate from side to side, as well as up and down, shaking the ground violently  Cannot move through liquids

 Surface Waves – P and S waves that reach the surface; move more slowly but produce the most severe ground movements

MEASURING EARTHQUAKE MAGNITUDE  Magnitude: measuring earthquake strength based on the seismic waves and movement along faults  Three ways to measure:  Mercalli Scale  Richter Scale  Moment Magnitude Scale

MERCALLI SCALE  Measures intensity (strength of ground motion in a given place)  Not precise  12 steps describe how quakes affect people, buildings and land surface  Same quake can have different ratings because it has different amounts of damage at different locations

RICHTER SCALE  Rates the size of seismic waves measured by a seismograph  Developed in 1930’s and used for about 50 years  Provides accurate measurements for small, nearby quakes  Does not work well for large or distant earthquakes

MOMENT MAGNITUDE SCALE  More commonly used today  Rating system that estimates the total energy released by an earthquake

 Can be used to rate earthquakes near or far

 Does not work well for large or distant earthquakes

DAMAGE DONE BY EARTHQUAKES  Building damage  Liquefaction: earthquake’s shaking causes loose soil to turn to liquid mud; often causes landslides  Tsunamis: when earthquake jolts ocean floor, this causes the floor to rise and push water; can form large waves called tsunamis

VOLCANOES

WHAT IS A VOLCANO?  Volcano: a weak spot in the crust where molten material (magma) comes to the surface  Constructive force (builds land)

 Magma: molten mixture of rock-forming substances, gases, and water from the mantle

 Lava: magma that reaches the surface; when cooled, it forms solid rock

LOCATION OF VOLCANOES  600 active on land, with many more beneath the sea  Form along the boundaries of Earth’s plates  Weak, fractured crust allows magma to reach the surface

 Most volcanoes occur along diverging plate boundaries (mid-ocean ridges) or subduction zones at the edges of oceans

 Some volcanoes form at “hot spots,” far from plate boundaries

LOCATION OF VOLCANOES

VOLCANOES @ DIVERGENT PLATE BOUNDARIES  Divergent boundary: plates divide; magma rises  Volcanoes form along the mid-ocean ridge  Rarely, these volcanoes rise above the ocean surface  Iceland  Azores Islands

VOLCANOES @ CONVERGENT PLATE BOUNDARIES  Convergent boundary: plates collide; oceanic crust melts/returns to mantle; magma rises  Volcanoes form where magma erupts through the surface as lava  Many occur on islands where two oceanic plates collide

 Island arc: a string of volcanoes that form islands at converging oceanic crusts     

Japan New Zealand Caribbean Philippines Indonesia

HOT SPOT VOLCANOES  Hot Spot: an area where magma from deep in the mantle melts through the crust like a blow torch  Often lie in the middle of plates, far from edges  Not a result of subduction (crust sinking/melting/rising)  Hot spots can produce a series of volcanic mountains as the plate drifts over the hot spot  Hawaii  Yellowstone National Park

VOLCANIC ACTIVITY  Magma is formed in the asthenosphere, where the rock becomes liquid  Magma rises because it is less dense than the surrounding solid rock  During a volcanic eruption, the gases dissolved in the magma rush out, carrying magma with them

INSIDE A VOLCANO  Magma Chamber: the pocket of magma beneath a volcano  Pipe: a long tube in the ground that connects the magma chamber to Earth’s surface  Vent: an opening in the volcano through which gases leave  Lava Flow: the area covered by lava as it pours out of a vent  Crater: a bowl-shaped area that may form at the top of a volcano around the central vent

INSIDE A VOLCANO

TYPES OF VOLCANIC ERUPTIONS  The silica content of magma determines whether the volcanic eruption is quiet or explosive  Quiet Eruptions: magma flows easily and relatively constantly  Explosive Eruptions: trapped gases build up pressure and explode

QUIET ERUPTIONS  The most common type of volcanic activity on Earth  Runny lava oozes from vent quietly and builds land over thousands of years  Ex: Mount Kilauea, Hawaii

 Produce two different types of lava:  Pahoehoe – fast moving, hot lava; looks like wrinkles  Aa – slow moving; forms a rough surface with jagged chunks

EXPLOSIVE ERUPTIONS  Thick sticky magma clogs up the volcano pipe like a cork in a bottle  Trapped gases build pressure until they explode into fragments of lava  Volcanic ash – fine rocky particles  Cinders – pebble-sized particles  Bombs – larger particles of lava from baseball to car-sized

 Pyroclastic Flow: occurs when an explosive eruption hurls out ash, cinders, bombs, and gases

LANDFORMS FROM LAVA & ASH  Shield Volcanoes – wide, gently sloping mountain made up of thin layers of lava that pour out and harden on top of previous layers  Cinder Cone Volcanoes – a steep, cone-shaped mountain made up of ash, cinders, and bombs piled up from explosions of thick magma

LANDFORMS FROM LAVA & ASH  Composite Volcanoes – tall, cone-shaped mountains with alternating layers of lava and ash from alternating quiet and explosive eruptions  Lava Plateaus – high, level areas of lava that floods and area and cools

LANDFORMS FROM LAVA & ASH  Calderas – a huge collapse of a volcanic mountain after an enormous eruption empties the magma chamber beneath the volcano; appears like a crater, but much larger