Geography Chapter 2.3
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  • 1.  Tectonic plates are massive, moving pieces of Earth’s lithosphere Plates ride above circulating, heated rock Geographers study plate movements to understand: - how the earth is reshaped  - how earthquakes and volcanoes are formed The largest plates are named after continents: page 37
  • 2.  Plates move in one of four ways: page 38-39 Divergent- by spreading, or moving apart Subduction - diving under another plate Convergent- collision, or crashing together Transform- sliding past each other in a shearing motion
  • 3.  Movement of plates effects surface of the earth Saudi Arabia–Egypt’s plates are spreading apart, widening Red Sea India’s plate is crashing into Asian continent, building up Himalayas
  • 4.  Peru-Chile Trench
  • 5.  Two plates meeting can cause folding, cracking of rock  -Platesmove very slowly  - Causes rocks to become more flexible and fold under pressure
  • 6.  Faults occur when pressure causes rock to fracture, or crack. -Sometimes the rock is not flexible and will crack due to plate movement The crack is called a fault Fault line is place where plates move past each other
  • 7.  As the plates move past each other at a fault, the earth shakes or trembles This movement may become violent, called an earthquake
  • 8.  Seismograph  -Special device used to detect earthquakes -Measures the size of the waves created by an earthquake
  • 9.  Earthquakes release energy in the form of motion, causing: - landslides  - land displacement  - fires (broken gas lines)  - collapsed buildings Richter Scale — numeric scale showing relative strength of earthquake  -Uses info from seismographs to determine the strength of an earthquake  -Has no absolute upper limit  -Major quake measures a 7 or more
  • 10.  Location in the earth where an earthquake begins is called the focus Epicenter — the point directly above focus on the earth’s surface - In most cases, the epicenter is the area that receives the greatest damage Nearly 95% of earthquakes occur at tectonic plate boundaries
  • 11.  Tsunami, a giant ocean wave, begins at epicenter of an earthquake: - travels at up to 450 mph  - waves of 50–100 ft. or higher May travel across wide stretches of the ocean and do damage on distant shores
  • 12.  On March 11, 2011 an 8.9 magnitude earthquake struck Japan. The earthquake and subsequent tsunami has caused vast amounts of damage and the death toll continues to rise. Nearly 16,000 people died as a result.
  • 13.  On December 26th, 2004, an earthquake caused by subduction caused a series of tsunamis along the coasts of the Indian Ocean. Some waves were said to be upwards of 98ft. high. Killing over 230,000 people, the 2004 tsunami is the worst natural disaster in history.
  • 14.  Volcanoes occur where there are cracks in the earth’s surface. Material, such as magma, pours out of the vent. Most volcanoes occur at tectonic plate boundaries
  • 15.  There are several types of eruptions— violent explosions where lava, gases, ash or dust are expelled from the vent in Earth’s crust Lava — magma that has reached the earth’s surface; may create landform
  • 16.  Ring of Fire — zone around rim of Pacific Ocean: - meeting point of eight tectonic plates  - vast majority of the earth’s active volcanoes located here
  • 17.  “Hot spots” are where magma rises to surface from mantle Hot springs, geysers indicate high temperatures in earth’s crust Some volcanic action is useful:  - volcanic ash produces fertile soil - hot springs are tapped for heat, energy