By Mr. D

 A volcano is a mountain that forms when magma reaches the surface of the Earth.  Magma rises because it is less dense than the solid rock around it.

What’s inside a volcano? Magma Chamber- molten rock that feeds a volcano Vents- cracks in the crust What is the difference between magma and lava?

 Shield Volcano a) Built from layers of lava b) Non-explosive eruptions c) Not very steep, but can be big

 Cinder Cone Volcano a) Built from pyroclastic material b) Moderately explosive, short eruptions c) Small in size, steep slopes

CComposite Volcanoes (Stratovolcanoes) a) Most common type b) Explosive eruptions and lava flow c) Built from pyroclastic material AND lava

 Hawaiian Type Characteristics 1. Gentle runny type 2. Very low silica 3. Flows like warm honey or maple syrup

 Strombolian Type Characteristics 1. Lava slightly thicker than Hawaiian type 2. Some silica 3. Flows like cake batter

 Vulcanian Type Characteristics 1. Thicker than Strombolian 2. Trapped gasses explode sending solid rock, smoke, and thick pyroclastic lava up into the air 3. High silica 4. Lava like peanut butter

 Pelean and Plinian Characteristics 1. Thickest Lava 2. Violent explosions 3. Very high silica 4. Sends rock, lava, gases and ash into the air. The ash may travel long distances, even blocking the sunlight.

 two tectonic plates diverge from one another.  The crust is very thin at mid-oceanic ridges due to the pull of the tectonic plates  The release of pressure due to the thinning of the crust leads to adiabatic expansion, and the partial melting of the mantle causing volcanism and creating new oceanic crust

 Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide  Water gets pushed in the mix, lowering the melting temperature of the overlying mantle wedge, creating magma  Even though the magma is high in silica, thus has the consistency of peanut butter, it may reach the surface causing a volcano

 Hotspots are formed by mantle plumes  The plume may come from deep inside the earth making it very hot  Hotspots make islands, like Hawaii

 Tomorrow we will look at some different volcanic rocks and minerals  After that we will watch a film about volcanoes