the way rocks deform structural geology Deformation of Rocks Sagami bay lithophaga bivalves Rock destroyers secrete acids Make hole bigger as they grow Live right in between high and low tide Fossil show us where sea levels were at one time 5 m row of holes No one living there anymore 1923 large earthquake rocks sagami lifted up 5 meters Plate tetonics and mountain moving Fold bent rocks originally deposited flat line A Maps a representation of Earth s surface I Introduction 4 things Scale Tells you the distance along the ground North arrow know where you are relative to earth s surface key know what symbols are title know what the map is referring to USGS United States Geologic Survey that covers 7 5 min latutiude and longitude Quadrangle Ratio one unit on the map is equal to x units of the same size on the ground Ex 1 inch on the map 24 000 inches on Earth Or after converting 1 inch 2000 ft Bar scale indicated by a line or bar with distances marked in miles feet or km Contour Lines elevation is indicated by contour lines A contour line is a line on a map connecting points of equal elevation Contour interval the elevation difference from one line to another The contour interval is usually printed on the topographic map Contour line on a map connecting points of elevation a topographic map b aerial photo Maptech 3D view Formation lithologic unit from over and underlying units and is mappable Mappable more than 10 units Dipping Sedimentary beds Orientation of deformed rocks we need some way to describe the distribution of geologic structures Strike bearing of a line define by the intersection of a bedding plane and the horizontal Dip acute angle between a bedding plane and the horizontal measured perpendicular to strike Compression a force that squeezes together or shortens a rock caused by stress Stress forces acting on a rock Tension stretching the body and tending to pull it apart Shear a force that pushes two sides of a body in opposite directions Plate boundary that tension would dominate divergent mid ocean ridge Plate boundary compression dominate convergent subduction zone Strain any change in the original shape or size of an object in response to stress acting on the object Elastic deformation a change in shape of an object under stress that disappears when the stress is removed Rocks are elastic Brittle deformation rupture the cracking and fracturing of an object under stress Permanent change Usually occurs along subplanar surfaces that separate zones of coherent material Plastic deformation smooth continous plastic deformation under increasing force Occurs by the slippage of atoms or small groups of atoms past each other in the deforming material Bends the rocks Factors that affect deformation Temperature Pressure Rock type Strain rate fast or slow strain The variation of these factors determines if a rock will fault or fold brittle occurs at shallow depths when rock is cold plastic occurs at greater depths when rocks are warmer Confining Pressure flowing plastic deformation Fold terminology fold a bend in rocks limb refers to the two sides of a fold fold axis a line drawn down the points of maximum curvature of each layer axial plane an imaginary surface that divides a fold symmetrically 2 types of folds Anticline a fold of rocks where the beds dip away from the center oldest rocks are exposed in the center Syncline a fold of rocks where bends dip towards the center youngest rocks are exposed in the middle Anticlines and Synclines normally get a bunch of them Symmetrical Asymmetrical and Overturned Folds Fold Terminology Plunging fold domes and basins Joint break in the rocks no movement or little movement under stress all the time and crack periodically Fault a break in a rock along which motion has occurred hanging wall footwall displacement 2 Faults Strike slip faults dip slip faults move up and down motion of the fault blocks parallel to the dip direction a Normal fault a fault in which the hanging wall has moved down relative to the footwall b Reverse fault the hanging wall Caused by compression takes place at the subduction zone c Thrust fault very low angle reverse fault older beds over younger beds Oblique slip faults Strike Slip Faults motion of the fault blocks parallel to the strike direction a left lateral strike slip fault thrust fault style of reverse fault Volcanoes Krakatoa Indonesia 1883 erupted Phreatic Eruption water is getting tied up with the plumbing system of the volcano water expands steam forms eruption occurs Erupted with 100 million tons of TNT 10 times the atomic bomb dropped on Hiroshima Effects leveled the island wiped an island off face of the earth loudest sound in recorded history heard 2 000 miles away in Australia Tsunami huge long period waves killed 36 000 people Volcanic ash fell over 700 000 km So much ash got up into the stratosphere 13 of sun s light was blocked out Lowered global temp for several years about 1 or 2 degrees Volcano mountanious accumulation of material geomorphic future Caldera huge crater at top of volcano 1 km in diameter Volcanic Neck sometimes sides erode away and vent is exposed May 1990 Eruption of Kileau Hawaii II Material Pyroclastic Eruption Arenal Volcano Costa Rica What comes out Lava slow moving Gases 70 percent water vapor 15 percent carbon dioxide 5 percent nitrogen 5 percent sulfur 5 percent other stuff Lake Nyos in a crater of a volcano 1986 Lake turned over and gasses escaped killed 1700 people Trying to vent out gasses at the bottom Pyroclastic piece of rock that com flying out Old vent pumice volcanic ash Ash rock material less than 2mm Tambora 1815 to east of Java largest eruption in recorded history 10x bigger then Krakatoa 150km cubed blown out material landing on surface Created eruption column Over 40km of ash in atmosphere up to stratosphere 1816 The Year Without Sun Snow in June in New England Crop failures widespread 10 000 people die no summer Toba 1800 km across 10x as large as crater lake 10x as big as Tambora about 740 000 years ago 800km cubed Super Volcanoes Yellowstone Caldera geisers with geothermal energy Toba may end civilization as we know it if it happened today III Volcanic Activity Magma Viscosity viscosity is resistance to flow Viscosity is a function of temperature Hotter Magma less viscious and vise versa and dissolved gasses gasses increase fluidity Aa Lava block form means it was out longer Pahoehoe Lava ropey form means it just came out of the ground Laki Fissue