VOLCANOES

VOLCANOES

Volcano Features• Magma chamber: contains the hot, liquid

magma• Vents: holes in the crust where the magma

rises to the surface• Crater: a funnel shaped pit at the top of a

volcano’s central vent• Caldera: a large, circular depression caused

by the roof of a volcano collapsing

Volcano features

Volcano features

What Causes Volcanoes?

• Scientists use models based on rock samples to “see” what is going on deep inside the Earth

• Volcanoes result from the buildup of rock around a vent

What Causes Volcanoes?

• Magma forms below the Earth’s surface in the lower crust and part of the upper mantle

• The temperature of the mantle is hot enough to melt any rock, but why doesn’t the mantle melt?

• The weight of the rock above the mantle creates a lot of pressure. This pressure keeps the mantle tightly packed so it remains a solid.

• A decrease in pressure causes magma to form

What causes volcanoes?

• Magma rises toward the surface of the Earth because it is less dense than the surrounding rock

• What is density?• Density is how much stuff can fit in a certain

space or how compact something is. Remember our density demo with water and the different examples?

Where Do Volcanoes form?

• The Ring of Fire!https://www.youtube.com/watch?v=IfAcAxX81tk

Where do volcanoes form?

• A lot of volcanoes lie directly on tectonic plate boundaries

• The plate boundaries surrounding the pacific Ocean have so many volcanoes (Ring of Fire)

• Volcanoes form at the plate boundaries because this is where the plates collide or separate from one another. It is easier for magma to travel up through the crust.

Tectonic Plate Separation

• When 2 tectonic plates separate and move away from each other it is a divergent boundary

• As they separate a deep crack called a rift forms

• Mantle rises to fill the gap, pressure decreases, and the mantle rock melts to become magma

• Magma continues to rise up through the rift to create new crust

• Usually occurs at the ocean floor

Tectonic Plate Collision

• When 2 tectonic plates collide it is a convergent boundary

• Usually occurs where a continental and oceanic plate collide

• The oceanic plate is more dense and moves below the continental crust. The movement of one plate under another is called subduction.

• As the oceanic crust moves deeper into the mantle, it gets hotter and pressure increases. Water in the oceanic crust is released and mixes with the mantle rock so it has a lower melting point.

How volcanoes are formed

Hot SPots• Volcanoes can also form at hot spots. For

example, the Hawaiian islands.• Hot spots are places on the Earth’s surface

that are directly above columns of rising magma called mantle plumes

• A hot spot creates a long chain of volcanoes

Volcanic eruptions• There are 2 types of volcanic eruptions:1) Non-explosive2) Explosive• Scientists compare the amount of water and

silica in magma to decide if a volcanic eruption is non-explosive, explosive, or in between

Non-Explosive Eruptions

• Lava is magma that flows onto the Earth’s surface

• Lava flows are rivers of red-hot lava• Some of the largest mountains on Earth were

created by repeated lava flows over many years

Explosive Eruptions• Clouds of hot debris and gas shoot out from

the volcano at very high speeds• Molten is blown into many pieces that harden

in the air• Many tons of solid rock can also be blasted

away

Predicting Volcanic Eruptions

• Extinct volcanoes have not erupted in the past and will never erupt again

• Dormant volcanoes are not currently erupting, but have erupted at some time in the past

• Active volcanoes are in the process of erupting or show signs of erupting in the near future

Predicting Volcanic Eruptions

• Volcanoes can be predicted by measuring:1) Small quakes2) Slope3) Volcanic gases4) Temperature from orbit

Small quakes• Active volcanoes produce small earthquakes

as the magma moves up to the surface and causes the surrounding rock to move

• The number and intensity of the small earthquakes increases right before an eruption and can be measured with a seismograph

Slope• Measurements of a volcano’s slope provide

clues to predict eruptions• Bugles may form as magma pushes against

the inside of the volcano• A tiltmeter is used to detect small changes in

the angle of the slope

Volcanic Gases• Measurements of the gases coming out of

volcano can help predict eruptions• The amount of certain gases is used to predict

eruptions. A change in the amount of gases means things are changing in the volcano.

Temperature from orbit

• Satellite images can help predict eruptions• These images record infrared radiation (IR) to

measure changes in temperature over time• Analyzing the images allows scientists to

decide if the volcanic site is getter hotter as magma pushes closer to the surface

What Erupts from a volcano?

• Magma erupts either as lava or pyroclastic material• Lava is produced by non-explosive eruptions. There

are different types of lava based on its consistency. What is consistency?

• Pyroclastic material are rock fragments crated by explosive volcanic eruptions.

• Pyroclastic material is formed:• when magma explodes from a volcano and becomes a

solid in the air• when rock is shattered by powerful eruptions

Pyroclastic material• There are 4 types of pyroclastic material:1) Volcanic bombs2) Volcanic blocks3) Lapilli4) Volcanic ash

Pyroclastic Material• Volcanic bombs are large blobs of magma

that harden in the air

• Volcanic blocks are the largest pieces of pyroclastic material and are solid rock blasted out of the volcano

Pyroclastic material• Lapilli means “little stones” and are pebble-

like bits of magma that become solid before they hit the ground

• Volcanic ash forms when the gases in magma expand very fast and the walls of the gas bubbles explode into tiny glass-like pieces

Types of Volcanoes• There are 3 types of volcanoes:1) Shield2) Cinder cone3) Composite

Shield Volcano• Built of layers of lava from repeated non-

explosive eruptions• Has gentle sloping sides• Spread out over a wide area

Cinder cone volcano

• Small volcanic cones made of pyroclastic material

• Has steep slopes• Spread out over a narrow area• Erupt only for a short time and occur in

groups on the sides of shield and composite volcanoes

Composite volcano• Also called stratovolcanoes• Most common type of volcano• Form by explosive eruptions of pyroclastic

materials followed by non-explosive eruption of lava

• The combination of both types of eruptions creates alternating layers of pyroclastic material and lava

Volcano activityFor the rest of the period you will build your own volcano in lab groups. You will need:• Oak tag and markers• Empty water bottle• Food coloringWhen you are ready, ask the teacher for:• Vinegar• Baking soda