GEOS 212 1st Edition Exam 1 Study Guide Lectures 1 10 The questions will take advantage of content from slides or videos or maps or diagrams we have seen used in class or HW simple velocity calculations no measuring required content from HW 1 3 Lecture 1 Ocean basins Characteristics of layers in Earth crust mantle lithosphere asthenosphere diagram CRUST part of chemical layering MANTLE part of chemical layering LITHOSPHERE Strong solid Plates crust plus uppermost mantle ASTHENOSPHERE Weak but NOT MOLTEN Rest of mantle and core Diagram Thicknesses of continental crust and oceanic crust CONTINENTAL 30km OCEANIC 7km Lecture 2 Spreading Center factory for making oceanic crust profile view diagram Height of the spreading center is 2km above surrounding sea floor Divergent boundaries are the longest about 28 000 miles mountain range on Earth Subduction zones how removes oceanic crust and creates continental crust Continents collide convergent boundary The friction of the two continents pressing against each other eventually breaks One plate dives or subducts under the other down into the athenosphere where is melts into magma which will eventually resurface at a spreading center somewhere to create new crust Subduction zone profile view know diagram How magma forms Is heated and melted in the athenosphere where it then rises to the surface to flow from volcanoes and form new crust Lecture 3 II History of spreading in South Atlantic North Atlantic Eastern Pacific Labrador Sea and Indian Ocean All continents used to be together in one mass Pangea We can look at the oldest sea floors near mid ocean ridges to estimate time two continents diverged Oldest sea floor 140mya anything older we must estimate with other methods III Rates of spreading rate is distance time usually km my or cm yr i Distance total length between continents ii Time age of oldest sea floor The edge of the continent is usually not sea level but the edge of the continental shelf measure from there for calculations IV Pacific Plate also has chain of islands from hot spot Hawaii Connection between mantle plume hot spot island chain i Plate moves over hot spot youngest island largest eventually re submerges as it ages and moves away from hot spot Rate of motion calculation distance time usually km my or cm yr V Subduction zones in continental and oceanic settings Oceanic crusts can subduct under either oceanic OR continental crust Continental crust never subducts under Subduction zones are deepest portions of ocean Trench Large earthquakes generally occur here VI Plate tectonics is The most efficient way for the earth to lose heat that s the simple reason that plates move VII Early idea was that conveyor belt convection drives plate but it has problems Problems o 1 Cells like to have sides of same dimensions o 2 Upper and Lower mantle at least partially isolated o 3 Would predict larger plates would go faster no correlation o 4 Spreading centers and all plate boundaries move with respect to each other o 5 Hard to explain sudden changes in plate motion VIII Some people now believe that plates slide away from ridges and toward subduction zones IX World Tour of subduction zones HW review Lecture 4 Volcanoes 1500 could erupt 20 erupting most of the time VOLCANOES Occur in four tectonic settings o o o o Spreading centers Hot Spots Subduction Zones Continents Pulling Apart Two main types of volcanoes o Shield Volcanoes o On oceanic crust o Not steep sides o Basalt high iron very hot o Not explosive o Not Hazardous o Lava flows runny o Strato Volcanoes o o o o o o On continental crust Steep sides Andesite lower iron cooler stif Explosive Hazardous Lava flows ash cinders pyroclastic flows Diagrams of Shield Strato Volcanoes Videos of shield volcano eruptions o o o o history o of volcanoes below sea surface 80 Importance of Kilauea Most ACTIVE largest on Temperature of lava 2 000 degrees Key to forecasting eruptions Eruption Nature of magma Hot runny NOT very explosive o Nature of basalt color texture Black smooth igneous earth o What else comes from volcanoes besides magma Magma Lava Andesite Basalt Ash Cinders o Pyroclastic flow made up of rock ash gases o Nature of andesite ash color texture Porous heterogeneous gray pockets of minerals o How many potentially active volcanoes 1 500 o How many people live at risk from volcanoes MANY ex san andres fault California Cascade volcanoes in Oregon Washington Stratos for by subduction Eruption history of the Cascade volcanoes Cascade volcanoes are some of the most dangerous due to their eruptive history and potential for future eruptions Caldera eruptions Yellowstone sits on top of four overlapping calderas explosive eruptions have occurred in and near the Yellowstone caldera Lecture 5 Review of volcanoes 1500 could erupt dormant 20 erupting today Shield volcanoes versus stratovolcanoes hazards Strato very hazardous explosive Shield Barely hazardous and not explosive prediction Strato less predictable erratic Shield relatively predictable consistant setting Strato Subduction zones Shield Hot spots Transform fault 3rd type of plate boundary Two types of plates just slide past each other not creating or destroying plate Friction builds up and break causing jump and earthquake Atlantic example San Andres fault Pacific example Haiti edge of Caribbean plate San Andreas fault transform fault North America Pacific plate boundary Animations of earthquake process stick build up stress then slip Earthquakes along San Andreas fault 922 earthquakes along fault in last week Many too small too report Magnitude threshold for detection MAGNITUDE 3 Sizes magnitudes of earthquakes 3 not detectable 2 5 5 5 6 1 7 0 8 0 to to to to or 5 4 6 0 6 9 7 9 greater Often felt but only causes minor damage Slight damage to buildings and other structures May cause a lot of damage in very populated areas Major earthquake Serious damage Great earthquake Can totally destroy communities near the epicenter Earthquake history along San Andreas fault 1857 Los Angeles roughly 8 3 occur on bendy part of fault 1898 quake in CA most famous in US history Global Earthquakes Sumatra Japan earthquake tsunami Global map of earthquakes with pattern of size and depths 30 000 500 100 20 One every 5 to 10 years Perspectives on big earthquakes earthquakes don t kill people buildings do Lecture 6 o o o o o o Global pattern of earthquakes last 20 years Plate tectonics helps understand modern world o 200Ma PANGEA oldest age of sea floor