SCIENCE G10 QUARTER 1

• Plates


  Sections of the Earth's crust and upper mantle that move around on top of the mantle like rafts
• Lithosphere


  Earth's crust and upper mantle that are broken into sections and move around on top of the mantle
• Plate tectonic theory


  1. Pieces of Earth's lithosphere are in constant motion, driven by convection currents in the mantle

  2. Plates move slowly in different directions

  3. Cause different geologic events like earthquakes and volcanoes
• What makes plates move?

  Convection currents in the mantle move the plates as the core heats the slowly-flowing asthenosphere (elastic/plastic like part)
• Mountain ranges


  • Formed by a variety of geologic processes, but the most significant ones are the result of tectonic plates
• Mountain system / Mountains belt


  A group of mountain ranges with similarity in form, structure, alignment that have risen from the same cause, usually an orogeny
• Mountain chain


  Consists of mountain ranges which differ in size and period of time
• Cordillera


  A community of mountains includes ridges, ranges, mountain chains and mountain systems
• Earth's lithosphere consists of

  • Crust
  • Upper part of mantle
• Crust


  • Made of a variety of solid rocks including sedimentary, metamorphic and igneous
  • Average density = 2.8 grams per cubic centimeter
  • Thickness ranges from 5 to 50km, thickest where there is a relatively young mountain and thinnest along the ocean floor
• Continental crust


  Thicker, less dense, composed of granitic rocks made up of lightweight minerals like quartz and feldspar
• Oceanic crust


  Thinner, denser, composed of basaltic rocks
• Variations in plate thickness are nature's way of partly compensating for the imbalance in the weight and density of the types of crust
• Plates change over time

  1. Plates composed partly or entirely of oceanic lithosphere can sink under another plate, usually a lighter, mostly continent plate

  2. This is happening now off the coast of Oregon & Washington where the small Juan De Fuca Plate is a remnant of the formerly much larger oceanic Farallon plate and will someday be entirely consumed as it continues to sink beneath North America
• 7 major tectonic plates

  • Pacific plate
  • North America plate
  • Eurasian plate
  • Antarctic plate
  • Indo-australian plate
  • South American plate
• Hawaiian islands


  Created by the Pacific plate, which is the world's largest plate at 39,768,522 sq. miles
• Minor plates


  • Juan De Fuca
  • Nazca
  • Scotia
  • Philippine
  • Caribbean
  • Very small plates or sub-plates
• Earthquake


  Stored energy suddenly released through a movement along a fault
• Fault


  Fracture or zone of fractures in rock
• Epicenter


  A point on the surface of the earth directly above the focus
• Focus


  Point within the earth where earthquake waves originate
• Seismic waves


  Waves emanating from the focus that can travel as surface waves or body waves
• Surface waves


  Don't travel through Earth, constrained to travel along surface of the earth from the epicenter
• Body waves


  Travel in all directions from the focus through the body of the earth, including P waves (primary waves) that travel faster and arrive first, and S waves (secondary waves) that lag behind the P waves
• Locating the Epicenter


  1. Requires recorded data from three different seismographs at significantly different locations, using the time it takes for P waves and S waves to travel and arrive at the seismographic stations

  2. Triangulation is the mathematical method for locating the epicenter or focus using three or more data sets from seismic stations
• Seismographs


  Instruments that record the seismic waves and create a seismogram to plot earthquake activity
• Time lag


  The time difference between P waves and S waves arriving at a seismograph station, with P waves traveling at 5.5 km/s and S waves at 3 km/s, a time difference of 2.5 km/s
• Epicenter distance


  1. Can be calculated using a map scale and drafting compass, setting the compass to the appropriate length distance from the location of the epicenter and drawing an arc

  2. Formula: D = Td/8 seconds x 100km, where D is the distance and Td is the time difference of P and S waves arrival
• Convergent Plate Boundaries


  Locations where lithospheric plates are moving towards one another, including oceanic-oceanic, oceanic-continental, and continental-continental convergence
• Subduction


  When one plate is more dense than another, the more dense plate goes underneath the less dense plate
• Subduction


  • Mt. St. Helens, where the Juan De Fuca plate goes under the North American plate
• Oceanic-oceanic convergence


  Where two oceanic plates collide
• Oceanic-continental convergence


  Where the thinner and denser oceanic plate is overridden by the thicker and less dense continental plate, causing the oceanic plate to descend into the mantle
• Collision


  When two plates of the same material and density buckle up and move to higher elevation
• Collision


  • Mt. Everest and the Himalayas, where plates are still colliding and gaining elevation
• Continental-continental convergence


  A powerful collision occurs where two thick continental plates collide, with both having a density much lower than the mantle, presenting subduction and causing extensive folding and faulting of rocks within the colliding plates
• Features of convergent plate boundaries

  • Trenches, varying depth of earthquakes, tsunamis, volcanic island arcs, mountain ranges
• Divergent plate boundaries


  Where two plates move apart
• Divergent plate boundaries on continents

  • Rift valleys, volcanoes, earthquakes, like the Great Rift Valley in Africa
• Divergent plate boundaries in oceans

  • Earthquakes, volcanoes, mid-ocean ridges, like the Mid-Atlantic Ridge in the Atlantic Ocean