De_Chem_1.6_Volcanoes

DE_Chem_1.6
Volcanoes

occurs when solid, hot material rises to Earth’s surface. As the pressure decreases, the rock material expands, and this lowers its melting point. This allows the rock to melt at a shallow depth in Earth’s interior, forming magma.

​

​Decompression Melting

​Lower pressure means lower temperature needed to melt rock into magma

​​Explosive: Decompression

Carbon dioxide goes from liquid to gas

​​Decompression

occurs when water or carbon dioxide is introduced to the rock material in the upper mantle. These materials lower the melting point of the rock material (similar to the way that salt lowers the melting point of ice). This causes the mantle rocks to melt at a shallow depth in Earth’s interior, producing a pool of magma.

​Flux Melting

Copper Pipe/Plumbing

Soldering w/ flux

Copper Pipe/Plumbing

Soldering w/ flux

Lowers the melting point

flux=contamination

Dropdown

Decompression melting is when rock melts at a​

Select answer

melting point due to a ​decrease in pressure as it nears Earth's surface.

Dropdown

Flux melting​

Select answer

the melting point of rock due to contaminants such as water and carbon dioxide mixing with the rock as it nears Earth's surface.

DE_Chem_1.6.2

-Hot-spots

​Non-boundary

-Divergent
-Convergent

​At boundaries

Where do volcanos form?

Most Common; less explosive

DivergentBoundary
Volcanos

Convergent Boundary Vocanos

​Occur at locations other than plate boundaries

Hot Spots

More explosive

-Hawaii is an example.
-A tectonic plate moves over the hotspot, creating a chain of volcanos
-These usually are in the middle of tectonic plates

​

​Hot Spots

Rich in Silica and sedimentary contaminants, including water
Usually at convergent boundaries

Explosive Volcanos

Usually at divergent boundaries

Non-Explosive Volcanos

Volcano grows from ocean floor but doesn't rise above the surface.

Sea Mounts

An oceanic volcanoe that has weathered/eroded down to sea level...corral grows and lagoons form.

​​Atolls

Dropdown

This type of volcano is not explosive because its magma has a ​

Select answer

silica content.

Dropdown

This volcano is explosive, containing a ​

Select answer

amount of silica in its magma.

DE_Chem_1.6.3

​Ultra-Mafic Magma	​Mafic Magma	Intermediate	​Felsic Magma
-​composed primarily of mafic minerals i.e. olivine -Most magma originates in the mantle, so most starts as ultra-mafic	​-rich in iron, magnesium, silicon and calcium	-Extrusive Rock includes andesite	​-rich in silica, aluminum and sodium

Changing from Ultra-Mafic to Mafic lava to Felsic Lava

​

​Magmatic Differentiation

​​Molten Glass is very viscous. It has a high silica content. Just like magma!

​​Everyday examples of viscous materials...SEE how they RESIST FLOW.

​​What does bread and lava rock have in common?

Multiple Choice

What type of gas makes holes both in bread and lava rock?

• Sulfur

• Oxygen

• Carbon Dioxide

Open Ended

Why do some types of lava rock have holes in it?

DE_Chem_1.6.4

​Basaltic Lava; low viscosity

​​Pahoehoe

Basaltic; jagged; high gas content = low density, high viscosity

​​aa lava

comes from Intermediate Magma

​​Blocky Lava

Reorder

Reorder the following lavas from least silica to most silica content

• Ultra-Mafic

• Mafic

• Intermediate

• Felsic

1

2

3

4

• 1
• 2
• 3
• 4

Intermediate Magma

Lassen National Park, CA

​Blocky Lava

Multiple Select

Which of these is an example of Tephra?

• pumice

• Lapilli

• Volcanic Bomb

• volcanic ash

​Tephra; <2mm in diameter

​​Ash/Dust

​Tephra; 2-64mm in diameter

​​Lapilli

Tephra; >64mm in diameter

​​Volcanic Block/Bombs

​Tephra; very low density due to trapped gas bubbles inside

​​Pumice

Cross Section

​​Shield Volcano

​Gentle Slopes due to multiple basaltic lava flows

​​Mauna Kea, Hawaii

​​Mt. Shasta, CA

​Lava doesn't flow far b/c very viscous; layers of lava and pyroclastic material;

​​Composite Volcano aka Stratovolcano

​​View from the top
Cinder Cone

​​Lassen National Park, CA

Match

Match volcanoes to their characteristics.

Shield Volcano;mafic/basaltic lava;broad

Composite Volcano; intermediate lava

Cinder Volcano; lava rich in gas; small

• Shield Volcano;mafic/basaltic lava;broad

• Composite Volcano; intermediate lava

• Cinder Volcano; lava rich in gas; small

​Caldera
Crater Lake, Oregon Summer 2025

​​Fissure Eruption