VOLCANOES

By Mr. D

What is a volcano?

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?

Types of Volcanoes

Shield Volcanoa) Built from layers of

lavab) Non-explosive

eruptionsc) Not very steep, but

can be big

Types of Volcanoes

Cinder Cone Volcano

a) Built from pyroclastic material

b) Moderately explosive, short eruptions

c) Small in size, steep slopes

Types of Volcanoes

Composite Volcanoes(Stratovolcanoes)

a) Most common typeb) Explosive eruptions

and lava flowc) Built from

pyroclastic material AND lava

Types of Eruptions

Hawaiian TypeCharacteristics

1. Gentle runny type2. Very low silica3. Flows like warm

honey or maple syrup

Types of Eruptions

Strombolian Type

Characteristics

1. Lava slightly thicker than Hawaiian type

2. Some silica3. Flows like cake batter

Types of Eruptions

Vulcanian Type

Characteristics

1. Thicker than Strombolian2. Trapped gasses explode

sending solid rock, smoke, and thick pyroclastic lava up into the air

3. High silica4. Lava like peanut butter

Types of Eruptions

Pelean and Plinian

Characteristics

1. Thickest Lava2. Violent explosions3. Very high silica4. Sends rock, lava, gases

and ash into the air. The ash may travel long distances, even blocking the sunlight.

Divergent plate boundaries

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

Convergent plate boundaries

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

Hotspots are formed by mantle plumes

The plume may come from deep inside the earth making it very hot

Hotspots make islands, like Hawaii

The End

Tomorrow we will look at some different volcanic rocks and minerals

After that we will watch a film about volcanoes