Volcanoes A mountain that forms when molten rock, called magma is forced to the Earths surface. A mountain that forms when molten rock, called magma is forced to the Earths surface.

Nonexplosive Eruptions Lava is defined as magma that flows onto the Earths surface. Lava is defined as magma that flows onto the Earths surface. Some lava may be sprayed into the air. Some lava may be sprayed into the air. Low gas content. Low gas content. Pose a greater threat to property than human life. Pose a greater threat to property than human life.

Explosive Eruptions Clouds of hot debris and gases shoot out from the volcano at supersonic speeds. Clouds of hot debris and gases shoot out from the volcano at supersonic speeds. Molten rock is blown into millions of pieces in the air. Molten rock is blown into millions of pieces in the air. Dust size particles may travel for years in the upper atmosphere. Dust size particles may travel for years in the upper atmosphere. Volcanoes shrink after explosion due to the used up magma in the magma chamber. Volcanoes shrink after explosion due to the used up magma in the magma chamber.

Definitions Magma chamber: under the volcano where magma is stored. Magma chamber: under the volcano where magma is stored. Vents: holes in the crust where magma and gas are released. Vents: holes in the crust where magma and gas are released. Plug: mass of solid lava that blocks a volcano’s vent. Plug: mass of solid lava that blocks a volcano’s vent. Geothermal energy: power made from heat within the Earth. Geothermal energy: power made from heat within the Earth. Geyser: fountain of hot water and steam erupting from the ground in a volcanic area. Geyser: fountain of hot water and steam erupting from the ground in a volcanic area.

3 Types of Volcanoes

Cinder Cone Made up of piles of ash and cinders that collect around the opening. Made up of piles of ash and cinders that collect around the opening. Steep sides and narrow base Steep sides and narrow base Very explosive due to thick magma and lots of water vapor trapped inside. Very explosive due to thick magma and lots of water vapor trapped inside. Located in South America. Located in South America.

Shield Cone Forms from easy flowing lava from cracks in the crust. Forms from easy flowing lava from cracks in the crust. Large mountains with gentle slopes. Large mountains with gentle slopes. Not explosive, magma is thin with little gas. Not explosive, magma is thin with little gas. Hawaiian Islands are shield volcanoes Hawaiian Islands are shield volcanoes

Composite Cone Combination of a shield and cinder cone. Combination of a shield and cinder cone. Eruptions can change drastically from easy flowing lava to some of the most explosive and destructive volcanoes. Eruptions can change drastically from easy flowing lava to some of the most explosive and destructive volcanoes. Example: Mt. St. Helens Example: Mt. St. Helens

Magma Water saturated Water saturated If contains lots of water it is more likely to explode. If contains lots of water it is more likely to explode. Compare it to shaking a can of soda then opening it up. Compare it to shaking a can of soda then opening it up. Water saturated magma is found along subduction zones. Water saturated magma is found along subduction zones. Example: Mt. St. Helens Example: Mt. St. Helens

Magma Continued Silica rich Silica rich Causes magma to thicken up. Causes magma to thicken up. Vents plug up Vents plug up Leads to more explosive eruptions. Leads to more explosive eruptions. Less silica equals to easier flowing and thinner lava. Less silica equals to easier flowing and thinner lava.

Types of Lava

1. Blocky Lava - Stiff - Cannot travel far from the erupting vent. - Forms a jumbled heap of sharp edged rocks.

More Lava 2. Pahoehoe Lava - Flows slowly - Looks like dripping wax - also looks like a glassy surface with rounded wrinkles

And more Lava… 3. Aa Lava - Hawaiian Lava - has a jagged surface - stiff lava that flows out quickly and forms a stiff crust -Lava underneath continues to flow, thus tearing the above crust and making it jagged

And more lava… 4. Pillow lava - Forms when lava erupts underwater - Forms rounded lumps

Pyroclastic material Produced when magma explodes from a volcano and solidifies in the air. Produced when magma explodes from a volcano and solidifies in the air. Produced when existing rock is shattered by eruptions. Produced when existing rock is shattered by eruptions. 3 types 3 types

Types of Pyroclastic Material

1. Volcanic bomb - Large blobs of magma that hardens in the air. - Produced from volcanoes with high silica content

More Pyroclastic Material… 2. Lapilli - Latin for Little stones - Pebble size bits of magma that become solid before hitting the ground.

More Pyroclastic Material… 3. Volcanic Ash -Forms when gas in stiff magma expands rapidly and the walls of the gas bubbles explode into tiny glass like shards.

Volcanic Depressions Craters Craters - the depressions that forms on the top of a volcano as a result from an explosion or collapse of material.

More Depressions… Volcanic Caldera Volcanic Caldera - Bigger than a crater, forms when magma chamber that supplied material to a volcanic eruption empties and its roof collapses.

Hot Spot Volcanoes Places on Earth that are directly above columns of rising magma called Mantle Plumes Places on Earth that are directly above columns of rising magma called Mantle Plumes Not located near plate boundaries Not located near plate boundaries Mantle plumes stay in same spot while the tectonic plate moves above it Mantle plumes stay in same spot while the tectonic plate moves above it