1. Eruptions

2. Bellringer 1/12/17 Thursday
On a clean sheet of paper, Write 1 statement from each of the following -A, B, C, and D.
A) Rhyolitic Rock (high silica content) –or- Basaltic Rock (low silica content) +
B) Thin magma/lava thickness -or- Thick magma/lava thickness
C) Mild Volcanic Eruptions –or- Very Explosive Eruptions
D) Strato/Composite Volcano –or- Shield Volcano

3. Making Magma Volcanic activity depends on composition of magma
Lava can be thin & runny or thick & lumpy

4. Magma Temperature Most rocks melt between 800-1200 °C
In Crust & Upper Mantle
Pressure
Increase with depth because of weight of rocks
High pressure increases melting temperature

5. Composition of Magma Amount of Gas & Silica
More gases dissolved = increased explosiveness
Dissolved gases = carbon dioxide, water vapor, sulfur oxide, sulfuric acid
Water vapor determines where magma forms
Water vapor decreases melting temperature

6. Composition Viscosity = Resistance to flow (how thick or thin it is)
Temperature & silica content affect viscosity
High viscosity = cool magma/thicker
High silica = thick & sticky
Traps gases, produces explosive eruptions
Low silica = thin & runny/low viscosity
Flow easily, produce quiet, non-explosive eruptions

7. Types of Magma - Basaltic
Less then 50% silica content
Low-viscosity magma/thinner
Gas easily escapes
Quiet/mild eruptions
Shield volcano formed
Ex: Kilauea & Mauna Loa

8. Types of Magma - Andesitic
50-60% silica content
Oceanic-continental subduction zones
Intermediate viscosity/medium thickness
Intermediate explosiveness
Strato/composite volcano produced
Send high volumes of ash & debris
Ex: Colima Volcano in Mexico

9. Types of Magma - Rhyolitic
More than 60% silica content
Magma mixes with water and silica
High viscosity/thick magma
Large volumes of gas trapped
Very explosive
Forms Strato/Composite Volcanoes

10. Explosive Eruptions
If lava is too viscous (thick) to flow, pressure builds up until an explosion
Tephra = pieces of solidified lava or pieces of crust
Classified by size
Ash = smallest tephra, diameter is less then 2 mm
Blocks = largest tephra

11. Ash Can rise into atmosphere
Tiny sulfuric acid droplets remain in stratosphere and block sun’s rays and decrease global temperature

12. Pyroclastic Flows Tephra + gases VERY HOT

13. In-Class Assignment
18.2 Study Guide WKT