Review Terms Test 3 Strike Dip Stress Strain o bearing of a line defined by the intersection of a bedding plane and the horizontal o acute angle between a bedding plane and the horizontal measured perpendicular to strike o Any outside force applied to a formation o the amount of deformation an object experiences compared to its original size and shape Compression o Stress that acts to shorten an object o Stress that acts to lengthen an object Tension Shear o Stress that acts parallel to a surface Factors of Deformation o Temperature o Pressure o Strain rate o Rock type o The variation of these factors determines if a rock will fault or fold o A change in shape of an object under stress that disappears when the Elastic deformation stress is removed o Rocks are elastic Brittle deformation o The cracking and fracturing of an object under stress o Permanent change o Usually occurs along subplanar surfaces that separate zones of coherent material o occurs at shallow depths when rock is cold Plastic deformation o Smooth continuous plastic deformation under increasing force o Occurs by the slippage of atoms or small groups of atoms past each other in the deforming material o occurs at greater depths when rock is warmer o An equal all sided pressure such as lithostatic pressure produced by overlying rocks in the crust of the earth Confining pressure Fold Hinge o a bend in rocks Axial Plane Limb o a line drawn down the points of maximum curvature of each layer o an imaginary surface that divides a fold symmetrically o refers to the two sides of a fold Symmetrical Fold o Axial Plane is vertical Asymmetrical Fold o Beds in on limb dip more steeply than those in the other o Both limbs in same direction but one limb has been tilted beyond Overturned Folds vertical Syncline o a fold of rocks where beds dip toward the center o youngest rocks are exposed in middle o U shape valley o a fold of rocks where the beds dip away from the center o oldest rocks are exposed in the center o n shape peak o a break in rock with no movement o A break in the rock along which motion has occurred Anticline Joint Fault Dip slip fault Foot wall o inclined fractures where the blocks have mostly shifted vertically o the rocks on the lower side of a vertical fault o The rocks on the top side of a vertical fault o A dip slip fault in which tension cause a rock to pull apart o A dip slip fault in which compression pushes rocks together o low angle reverse fault o Motion of the fault blocks through shear parallel to the strike Hanging wall Normal fault Reverse fault Thrust fault Strike slip fault direction Volcano o An opening in the earth s crust through which molten lava ash and gases are ejected Phreatic eruption o occurs when magma heats ground or surface water The extreme temperature of the magma causes near instantaneous evaporation to steam resulting in an explosion of steam water ash rock and volcanic bombs o The pipeline in the center of the volcano that connects to the magma Crater Vent o The opening at the top of a volcano chamber beneath Caldera Volcanic neck o A crater greater than 1km large o a column of solidified lava or igneous rock formed in a volcanic vent especially when exposed by erosion Lava Volatiles Pyroclastics o Molten rock that is spewed from a volcano o volatile components of magma mostly water vapor and carbon dioxide that affect the appearance and explosivity of volcanoes o a fluidized mixture of solid to semi solid fragments and hot expanding gases that flows down the flank of a volcanic edifice o the massive clouds that flow out of volcanoes Volcanic ash o tiny fragments of jagged rock minerals and volcanic glass o Unlike the soft ash created by burning wood volcanic ash is hard abrasive and does not dissolve in water o A type of lava found in Hawaii that does not have a lot of volatiles so it cools in a chunky shape o A type of lava found in Hawaii that has more volatiles so it cools very Aa Pahoehoe smooth Viscosity o the ability of a substance to resist flow o the more silica a lava has the more viscous it is Basalt lava 50 silica Andesite lava 50 silica Rhyolite lava 70 silica Flood basalts from a fissure o a very extensive lava flow of basaltic composition that has issued o often to be found as part of a series of such flows one on top of another forming a plateau Shield volcano o Low viscosity lava flows Low silica magma Basalt o Gently sloping flanks between 2 and 10 degrees o Tend to be very large Mauna Loa Cinder Cone o one of five volcanoes that form the Island of Hawaii o the largest subaerial volcano in both mass and volume and has historically been considered the largest volcano on Earth o Formed of pyroclastics o Steep sides 30 degrees o Relatively small o Rapid growth o Short duration of activity Composite or Stratovolcano o What are thought of as typical volcanoes o Alternating pyroclastic layers and lava flows o Slopes intermediate in steepness o Intermittent eruptions over long time span o Mostly andesite o Distribution Circum Pacific Belt Ring of Fire Mediterranean Belt Mt St Helens o Composite volcano in Washington o March it started to steam o April it started to tremor o Mid april north side started to bulge o May 18 magnitude 5 eruptions blow out of the side of the mountain Lahar o A volcanic mudflow o A mixture of water and pyroclastic material in a concrete like slurry capable of moving up to 100 km hour Erupting column eruption o consists of hot volcanic ash emitted during an explosive volcanic o The combination of the gas thrust region convection region and umbrella regions o Divided by the fragmentation surface Gas thrust region o At the base of the plume material is forced upwards out of the vent by the pressure of expanding gas mainly steam o The gas expands because the pressure of rock above it rapidly reduces as it approaches the surface o typically reaches to only one or two kilometres above the vent o covers most of the height of the plume o The gas thrust region is very turbulent and surrounding air becomes mixed into it and heated o The air expands reducing its density and rising Convective region o The rising air carries the solid and liquid material from the eruption entrained in it upwards Umbrella region o The area in the stratosphere where the temperature of the plume reaches the same temperature as the air o At this point the plume stops rising except for the momentum it already has Pyroclastic flow Earthquake o Mixture of hot gases ash and