1. OBJECTIVES: Types of Magma Anatomy of a Volcano Types of Volcanoes

2. Viscosity: Resistance of a liquid to flow
There are 3 types of magma. They range from very runny (low viscosity) to very sticky (high viscosity).

3. Anatomy of a Volcano Lava erupts through an opening called a vent.
Over time, the cooled & solidified lava forms a mountain known as a volcano.
At the top of the volcano, there is a bowl-shaped depression that can vary in size:
Crater: Smaller in size
Caldera: Larger in size.
Over 1 km in size
Forms when top of volcano collapses into the magma chamber.

4. Lava vs Magma
Magma – molten rocks located within the interior of the Earth
Lava – molten rocks located on the surface/exterior of the Earth

5. Caldera
Crater

6. Anatomy of a Volcano
Volcanic fragments thrown into the air during eruptions are called tephra.
Can be newly cooled & hardened lava, crystallized mineral grains, or pieces of volcanic cone.
Categorized based on size.
Dust Size: Small
Volcanic Bombs: Large, rounded tephra.
Volcanic Blocks: Large, angular tephra.

7. Anatomy of a Volcano
Pyroclastic flow are clouds of gas, ash, & other tephra down a slope at incredible speeds.
A.K.A. Rapidly moving volcanic material!
Can cause death & tremendous damage!

8. Composite (Stratovolcano)
Types of Volcanoes
Shield
Cinder-Cone
Composite (Stratovolcano)

9. Shield Volcano Gently sloping sides Nearly circular base
Forms when layers of basaltic lava accumulate during non-explosive eruptions
Low viscosity magma: Basaltic Magma
Ex. Hawaiian Islands

10. Cinder-Cone Volcano
Forms when material ejected high into the air falls and piles up around the vent.
Usually has steep sides
Generally small in height
Has more silica than shield and large volumes of gases
Explosions are more severe than shields: Andesitic Magma

11. Composite Volcanoes
Forms when layers of volcanic fragments alternate with lava.
Large amounts of silica and gas: Rhyolitic magma.
Much larger than cinder-cone.
Violently explosive: Harmful to humans & environment
Ex. Mt. Saint Helens

12. Where Do Volcanoes Occur?
Most occur at plate boundaries
80% along convergent
15%along divergent
5% occur far from plate boundaries.

13. Convergent Volcanism Circum-Pacific Belt A.K.A. “Ring of Fire”
Volcanoes of the Western U.S., Japan, Philippines, & Indonesia
Ex. Mt. Saint Helens
Mediterranean Belt
Volcanoes of Italy
Mt. Vesuvius

14. Ring of Fire

15. Divergent Volcanism Most occur along ocean ridges.
Plates are pulling apart and magma wells up into the gap, producing volcanoes and lava flows.

16. Hot Spots
The volcanoes that are formed far from plate boundaries are formed because of hot spots.
Hot Spots: areas of intense magma temperatures.
As a plate moves over a hot spot, the temperatures melt the crust and the new magma rises to form volcanoes.
When this happens, you get a string of volcanoes
Ex. Hawaiian Islands