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End Warm-up Name and describe the three types of plate boundaries? Distinguish between continental crust and oceanic crust. This bar timer, will start when anywhere on the slide is clicked. The bar will move from left to right and the word ‘End’ will appear at the end, accompanied by a ‘Deep Gong’ sound. It is possible to change the duration of this timer to any time, by entering the animation settings, and changing the timing for ‘rectangle 3’. Note the time has to be entered as a number of seconds – so if you want 2mins & 30secs – this is entered as 150 (60X2 + 30 = 150). End

Wednesday, January 11, 2017 Warm-up Review Volcanos and Earthquakes Work on Midterm Review Homework: Midterm Exam Review due 1/17

Volcanoes

A Volcano is… An opening in Earth’s crust through which molten rock, gases, and ash erupt. Also, the landform that develops around this opening.

Where Volcanoes Form Most volcanoes occur at: DIVERGENT boundaries, and at CONVERGENT boundaries that have SUBDUCTION. Hot Spots

Volcanoes at Divergent Boundaries Decrease in pressure as plates pull apart lets magma rise. These fissure volcanoes are located at the Mid-Atlantic Ridge and the Great African Rift Valley

Volcanoes at Convergent Boundaries (Subduction) Subduction increases the amount of water in the asthenosphere, which lowers the melting temp. As the denser oceanic crust is pushed lower, it melts into magma. When continental and oceanic plates converge, a volcano forms on land. When 2 oceanic plates converge together, a volcano forms an island. Mount Hood/ Portland

Hot Spots We call these HOT SPOTS. Sometimes, volcanoes occur at places that aren’t plate boundaries. We call these HOT SPOTS. Hot spots are areas where hot magma rises from deep in Earth’s mantle. Magma escapes where the crust is the thinnest or weakest. It starts out solid then it melts when it reaches areas of lower pressure.

Volcanoes that make up Hawaii. Example of Hot Spot Volcanoes that make up Hawaii.

Shield Volcanoes Cinder Cone Volcanoes Composite Volcanoes Types of Volcanoes There are 4 main types of Volcanoes: Shield Volcanoes Cinder Cone Volcanoes Composite Volcanoes Fissure Volcanoes

Shield Volcanoes Shield Volcanoes form from runny lava (low viscosity) that tends to flow long distances before hardening. They generally have quiet eruptions. Volcano has a broad base and gently sloping sides. Volcano has a less explosive eruption than other types because the lava flows more easily Type of magma- Mafic Basalt: black, runny lava Made of layers of lava Example: Mauna Loa, Hawaii

Cinder Cones Form when molten lava is thrown into the air from a vent. As it falls, it breaks into fragments called ash or tephra that harden before hitting the ground. The ash and tephra make a cone-shaped mound. They are smaller than other types. Erupt explosively because magma is thick, which allows pressure to build up. Magma composition: Felsic Rhyolite (light colored)

Example: Krakatau, Indonesia

Cinder Cones New Guinea Iceland

Composite or Stratovolcano Form from alternating eruptions of quiet lava and explosive ash. The layers build up and make a moderate-sized volcano. Most common kind of volcano Made of layers of ash/tephra and lava. Magma composition- Andesite: medium color

Example of Composite/Stratovolocano Mt. Pinatubo-Philippines

Fissure Volcanoes Form in long cracks where plates are pulled apart and near other volcanoes where the crust is weakened. Cinder Cone or Shield Volcanoes may also be nearby.

How does a Caldera Form? A) A Volcano’s pressure starts to build up B) The Volcano releases large amounts of Lava C) As the Lava is released, the pressure decreases and the volcanic mountain begins to collapse, forming a concave shape in the center of the volcano. D) The center of the volcanic mountain may begin to fill with water and form a lake.

Viscosity The hotter the magma or lava, the lower the viscosity. The viscosity of magma and lava depends on both temperature and composition. The hotter the magma or lava, the lower the viscosity. Magmas and lavas high in silica have higher viscosities than magmas and lavas low in silica.

Magma How Magma Forms Magma is a mixture of molten rock, suspended mineral grains, and dissolved gases that fuels all volcanoes. Magma forms when temperatures are between 800°C and 1200°C. Such temperatures exist at the base of the lithosphere and in the asthenosphere.

Magma How Magma Forms Pressure Pressure, which increases with depth, is one factor that determines whether rocks will melt to form magma. As pressure increases, the temperature at which a substance melts also increases. Due to the effects of pressure, most of the rocks in Earth’s lower crust and upper mantle do not melt to form magma.

Magma Types of Magma Basaltic Magma Basaltic magma typically forms when rocks in the upper mantle melt. Most basaltic magma rises relatively rapidly to Earth’s surface and reacts very little with crustal rocks because of its low viscosity. The volcanoes fueled by basaltic magma erupt relatively quietly. Basaltic magma is rich in Iron and Magnesium but low in silica (50%)

Magma Types of Magma Andesitic Magma Andesitic magma is found along continental margins, where oceanic crust is subducted into Earth’s mantle, and is formed from oceanic crust or oceanic sediments. Andesitic magma contains about 60 percent silica, resulting in an intermediate viscosity. The volcanoes it fuels are said to have intermediate eruptions.

Mt. Fuji, Japan Mt. St. Helens, Washington State, USA

Magma Types of Magma Rhyolitic Magma Rhyolitic magma forms when molten material rises and mixes with the overlying silica- and water-rich continental crust. (70%+) Silica content. Rhyolitic magma has high viscosity and fuels very explosive volcanoes.

Earthquakes

Forces Within Earth What is an Earthquake? Earthquakes are natural vibrations of the ground caused by movement in Earth’s crust. In other words: **When the ground shakes**

Forces Within Earth There are 3 kinds of stress acting on rocks: 1. Tension Compression Shear

Forces Within Earth Tension -- is stress that pulls a material apart.

Forces Within Earth Compression -- is stress that decreases the volume of a material. It is the force of squeezing together.

Forces Within Earth Shear -- is stress that causes a material to twist or tear.

Forces Within Earth Each force creates movement in rock along a fault. What is a fault? Faults are cracks or systems of cracks along which movement occurs.

Forces Within Earth There are 3 types of faults: Normal Reverse Strike-slip

Forces Within Earth Normal Faults occur when rocks on one side of the fault drop down as compared to rocks on the other side. Tension force creates normal faults. Occur at divergent plate boundaries. Pulling FOOTWALL

Forces Within Earth Squeezing HEADWALL Reverse Faults occur when rocks on one side of the fault are pushed up and over rocks on the other side Compression force causes reverse faults. Occur at convergent plate boundaries.

Forces Within Earth Strike–Slip Faults -- occur when rocks on opposite sides of the fault move horizontally past each other. Shear force causes strike- slip faults. Occur at transform plate boundaries.

Forces Within Earth Earthquakes create 3 types of seismic waves: Earthquake Waves Earthquakes create 3 types of seismic waves: 1. Primary waves 2. Secondary waves 3. Surface waves

Forces Within Earth Primary waves or P-waves, squeeze and stretch rocks in the same direction as the waves are traveling. P-waves are able to travel through anything (solid,liquid,gas).

Forces Within Earth Secondary waves or S- waves, cause rocks to move at right angles to the direction of wave movement. S-waves are able to travel through solids but not gases or liquids.

Forces Within Earth Surface waves travel along Earth’s surface, moving in two directions as they pass through rock. Surface waves “roll” like a water wave and cause the most destruction.

Forces Within Earth P-waves and S-waves are also called body waves because they pass through and begin in Earth’s interior. The point inside the Earth where the first movement of an earthquake occurs is called the focus. The point on Earth’s surface directly above the focus is called the epicenter.

Forces Within Earth P and S waves begin here