Geography Tectonics

• Earthquakes happen when rock masses on either side of a fault are pushed by tectonic forces. Friction causes them to get locked and stress builds up. When the stress exceeds the strength of the fault, the rocks snap or suddenly move to a new position. This sudden movement causes seismic waves to be released resulting in ground shaking.
• Shaking is generally felt most strongly near the epicentre.
• The greater the seismic energy released during an earthquake, the greater the magnitude.
• Stratovolcanoes form when high viscosity magma rises through weak areas in the crust to the earth's surface and erupts explosively as lava, ash and rocks. The ash and rocks settle on the sides of the volcano and are later covered by the lava. Over successive eruptions, a tall volcano consisting of alternating layers of ash and lava develops. As the highly viscous lava travels a shorter distance before cooling and solidifying, the volcano has steep sides and a narrow summit. Etc: Mount Mayon in Philippines.
• Shield volcanoes form when low viscosity magma rises through weak areas in the crust to the earth's surface and erupts effusively. Over successive eruptions, a volcano consisting of layers of lava develops. As the less viscous lava travels a longer distance before cooling and solidifying, the volcano has gently sloping sides with a broad summit. Etc: Kilauea in Hawaii USA
• Pyroclastic flows are hot clouds made of gas, ash and rocks travelling down the slopes of a volcano.
• Lahars are mudflows comprising of volcanic ash and water.
• Tsunami is a series of ocean waves which can be caused by undersea earthquakes, volcanic eruptions and landslides.
• The largest concentration of earthquakes is at the Pacific Ring of Fire.
• Earthquakes occur more commonly along convergent plate boundaries at subduction zones as more stress is built up during subduction.
• Broad belt around the Pacific Ocean where most earthquakes and active volcanoes occur comprises of all 3 types of plate boundaries.

  Convergent: Pacific plate moving towards Philippines plate. (PP)

  Divergent: Pacific plate moving away from Cocos plate. (PC)

  Transform: Pacific plate sliding past North American plate at the San Andreas fault (PNA)
• The tectonic hazards from earthquakes are ground shaking, tsunami, landslides and soil liquefaction.
• Stratovolcano's characteristics is its lava has high viscosity and traps gases which makes it very explosive. Its features are that it has a narrow base and a narrow summit. They are typically found in Convergent Plate Boundaries.
• Shield volcano's characteristics is its lava has low viscosity and does not trap gas which makes it effusive. Its features are that it has a wide base and a broad summit. They are typically found in Divergent Plate Boundaries.
• The benefits from earthquakes are fertile soil, extracting precious minerals and fossil fuels, geothermal energy and tourism activities.
• The hazards caused by volcanic eruptions are tephra, volcanic gases, lava flows, pyroclastic flows, lahars and volcanic landslides.