Lecture 08 09 29 2013 Phreatomagmatic Eruptions interruption between lava and water There wil be gas but it will be steam from flash heating of water Explosions with steam Explosions are localized to the contact Diamond head Oahu ring of pyrocastic debris Crater is very wide Fairly small volcanoe w very large crater Hard to erode o Called a tuff ring produced by accumulation of debris from phrea explosions Very prominent around the coast Lava and water o If enough pressure forms pillow basalts o If close to surface forms phreatic eruptions steam explosions o Product is tuff ring seashore or maars on land interaction w o Can form new islands anak Krakatau formed by phrea ground water followed by strombolian o Surtsey Eruption 1963 In Iceland Continued volcanic activity under water on the side of the island and eventually makes a cone Can be quiet underwater forming pillow basalts but the activity can become explosives Eventually the island will have no longer interaction w water and the eruption changes stlye and becomes mafic lava flow o Anak krakatau 1927 Phrea activity Was not as intense as surtsey As a result erosion from the ocean has erased the island Has pyrocastic debris but still growing The son of Krakatau 1883 was a caldera collapse Earthquake Legends Middle east o Biblical earthquakes Biggest and most controversial caused the fall of the walls of Jericho circle the city 7 times Jerusalem Saul battling the philistines India Asia o The world turtle Widespreak myth in india china and native americans says the world rests of for elephants on top of a turtle balanced on a cobra The earth is the lower shell of a turtle with the sky the heaveens as the upper shell and atmosphere inside earthquake happens when everyone moves o Namazu japan mythical catfish Under the isles of japan When the fish tries to escape that s the earthquake Native American myth o Mexican vaqueros California indian god made a rip in the ground so he can come back and forth and stir up mischief association between earthquakes and actual break in the ground talk about the fault o Gabriellano Indians southern California beautufil land with lakes and rivers with turtles One day the turtles argue and they swim away from each other After the san fransisco earthquake in 1906 they make the actually scientific discovery of the separation of the land responsible for earthquakes Fenris norse o Giant wolf associated with faults also o Not many earthquakes here so why a myth There were 1000 years ago So must be a really ancient legend Greeks rocks associated with it o Large earthqyuake tsunami because of Poseidon Archeology Evidence Ground disturbance o Folding landslides Fallen columns Collapsed walls Displaced arches Fires Earthquake victims Hippos Israel Jokahlups subglacial very dangerous eruptions for punctured glacier Lecture 09 Faults 09 29 2013 Earthquakes happen on faults Layers of stone do not continue on other side rocks have moved Offset fundamental characteristic of a fault different levels of against each other layer San andreas fault in CA very big fault o Appears as a long crack through the earth Different rock types on both types but hard to see what types of rocks Sometimes faults do not get to the surface but pushes rocks above other rocks This is the san Gabriel mountains Fault truncates layers could be easy to erode seem like notches fault scarp fault slides down the earth this is how mountains form active fault offsets stream channels happens instead of mountains 3 different movements of faults and all form scarping o reverse banding of layers that are both the tip o stripe slip make cracks or mud volcanos along fault o normal only one that gets exposed on the earth faults are noticed bc of the differences in rock composition what is a force Force is a push or a pull Newtons law a force imparts momentum induces acceleration of a mass As mass accelerates its velocity increases Will it deform What is a stress Force per area What happens if same amount of force is applied to two wooden pillars od different thickness Stress induces strain In object and object will DEFORM As stress increases object deforms Stress induces strain Faults are response in the earth to different stresses Different streses types o Confining pressure comes from every direction Comes from weight of the rocks o Differential stress different directions Forms a fault No other ones Force some part of a rock to move in respect to other parts o Fluids inside rocks and contract effects of stress and pressure How rocks respond to force and stress o Displacement breaks and faults o Rotation layer of rock tilts up o Strain push rocks up No fault formed As you increase stress in rocks change in behavior of material o Small stress little or no deformation Brittle deformation local Happens at surface Ductile distributed equally around the rock Happens in lower layers of the earth The transition between brittle and ductile happens between 15 20 km depth In the continental crust we have earthquakes because of A fault is a crack in the surface of the earth A fault can be a plane It is somewhere inside the earth o Two terms important strike and dip of fault plane Strike like a dip but water intersects the fault plane itself The line between the water and rock points a certain direction It is the direction that that line is pointing to A number of degrees counter clockwise Means line that intersects water and fault points towards north 20 degrees Dip tells if it is steep or not If you have water running down it will be straight down and it gives us the direction of the dip If the water runs north or south the dip runs east to west A low dip angle is almost horizontal 90 degrees is vertical Different types of behaviors for strikes and dips that transition Fault Classification o Strike slip fault rocks move horizontally Left lateral and right o Dip slip fault normal faults and reverse faults Normal hanging wall is moving down Reverse fault hanging wall is o Oblique slip difficult near the surface but happens in depth of lateral faults moving up the earth Reverse faults do not always break through to the surface At the tip of the fault You may be able to fold the layers Relationship between folding and faulting Big bend fault seems to be bending and as the pacific plate moves north material gets jammed against the bend Riddled w thrust faults San andreas fault is an example Tectonic Environment Plate motions o Move apart divergent and can be