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Social Studies :Grade 6 Unit two Lesson 1 (Earthquakes) The Earth consists of these layers : inner core, outer core, mantle and crust. The lithosphere which consists of the crust and the upper mantle , is where the earth’s tectonic plates are found. The lithosphere is the name of the place where an earthquake occurs on the surface of the earth. -The tectonic plates are constantly shifting , but when the plates move against each other , they can build up tension and pressure, which cause earthquakes . -When the tectonic plates move against each other causing an earthquake, they leave cracks on the earth’s surface which are called faults. A fault may move horizontally or vertically or both at the same time. Epicenter is the point on the Earth's surface that is directly above the focus (the point of origin) of an earthquake ,and underneath is called the hypocenter. When an earthquake happens, the energy released and radiates out from where the earthquake originated . *The ripples of energy are called seismic waves. Scientists use an instrument called seismograph to measure the size of the earthquake and how powerful it was. Lesson 2 (Volcanoes) A volcano is a vent in the Earth’s crust that releases some of the following volcanic matter :lava ,ash, gases and pyroclastic flow. *Types of volcanoes: 1-Shield Volcanoes: are the largest volcanoes in the world. They are made up of basalt, a generally dark volcanic lava that is made up of silica and rich in iron and magnesium. Shield Volcanoes do not explode like Strato Volcanoes. 2-Strato Volcanoes: are the most common type of volcano on Earth. They are made up of half lava and half pyroclastic material. This combination creates a much more thick and sluggish lava than basalt. It makes more gases causing the volcanic vents to get blocked ,which is why Strato Volcanoes have more explosive eruptions than others. These volcanoes are prone to mudslides , landslides and avalanches. 3-Cinder Cones: are uncommon and formed only by what is called a Strombolian eruption. * Types of Volcanic eruption: 1-An Icelandic eruption: is the least explosive volcanic eruption. 2-Hawaiian eruption : is very similar to Icelandic eruptions. 3-Strombolian eruptions: very little or no lava comes out of it. 4-Vulcanian eruptions: are bigger than Strombolian, these eruptions create Strato volcanoes. 5-Pelean eruptions. 6-A Plinian eruptions.