Chapter 17 VOLCANOES Volcanoes Volcanoes vents in the

Chapter 17 VOLCANOES

Volcanoes �Volcanoes - vents in the Earth’s surface where magma and gas arise. �Lava – Magma on top of the Earth’s surface.

What is inside a volcano? �Magma Chamber- the body of molten rock that feeds the volcano. �Vent – an opening at the surface of the Earth through which volcanic material passes.

What makes up Magma? �The make-up (composition) of the magma affects how violent an eruption is. �Lots of Water and Magma = Explosive. - When magma quickly moves to the surface, the water turns to gas. The gas expands quickly. �Magma and Silica = Explosive. - it is very thick and it clogs the vents, which builds pressure.

What Erupts from a volcano? �Lava �Pyroclastic material – hard magma

Types of Lava �Aa – fast pouring lava that forms a brittle, jagged crust.

Types of Lava �Pahoehoe- slowly flowing lava that has a glassy surface with rounded wrinkles.

Types of Lava �Pillow lava – forms when lava erupts underwater.

Types of Lava �Blocky lava – forms near the vents and looks like jumbled heaps of sharp-edged chunks.

Types of Pyroclastic Material �Volcanic bomb – large blobs of magma that harden in the air.

Types of Pyroclastic Material �Volcanic blocks– solid rock.

Types of Pyroclastic Material �Lapilli- means “little stones. ” Bits of hardened magma.

Types of Pyroclastic Material �Volcanic ash – forms when gases expand rapidly. (The most common type. )

Pyroclastic Flows � These are produced when enormous amounts of hot ash, dust, and gases are ejected from a volcano. � This cloud can move more than 124 mph � The temperature can be more than 1, 292 degrees F.

Types of volcanoes �Shield volcanoes – made of layers and layers of lava. Spread out over a large area. Sides are not steep

Types of volcanoes �Cinder Cone Volcanoes – made of pyroclastic material. Have steeps sides.

Types of volcanoes �Composite Volcanoes - Most common type. Made from alternating layers of pyroclastic material and lava. Broad bases and steep sides.

Volcanic Landforms �Craters – a funnel-shaped pit near the top of the central vent of a volcano.

Volcanic Landforms �Caldera – a large, semicircular depression that forms when the magma chamber below a volcano partially empties and causes the ground below to sink.

Volcanic Landforms �Lava Plateau – wide flat areas of land that result from lava that spread out over a large area.

Where Volcanoes Form �Most form near tectonic plate boundaries. �Magma is able to form and move up to the Earth’s surface. �Some form over “hot spots; ” areas that have a lot of magma under them, but are not near a plate boundary.

Chapter Review �Page 470 -471 �Don’t write the questions. �Do not do #17