1. Volcanoes
Lab 5

2. Concepts Location of active volcanoes Volcanism
3 categories
Viscosity
5 types of extrusive volcanism
Examples of each
3 types of lava flows
Dangers of volcanic eruptions

3. What do you notice about their locations?

4. Volcanism Definition: the origin and movement of magma
Three categories
Extrusive: magma is expelled onto surface
Intrusive: magma solidifies in the shallow crust near the surface. Can be exposed after weathering.
Plutonic: magma solidifies deep inside the crust.
Viscosity: The ability for lava to flow. Reflective of the amount of silica present in the magma.
LOW silica = LOW viscosity = nonexplosive
HIGH silica = HIGH viscosity = explosive

5. Volcanism Extrusive Examples
Mt. Shasta, CA
Mt. Fuji, Japan

6. Volcanism Intrusive Examples
Right: Stone Mountain, GA
Below: Devil’s Tower, WY

7. Volcanism Plutonic Examples

8. 5 Types of Extrusive Volcanism 1. Shield Volcano
Central vent allows magma from chamber to spill out, slowly building the volcano in layers.
Produces wide, gently sloping mountains
Best example: Hawai’ian volcanoes (right: Mauna Loa)

9. 5 Types of Extrusive Volcanism 2. Composite Volcano
“Stratovolcano”
Central vent allows magma to come up from chamber below
Produces symmetrical, steep-sloped mountains
Most “explosive” type of volcano
Examples: Mt Fuji, Mt Shasta, Mt St Helens

10. 5 Types of Extrusive Volcanism 2
5 Types of Extrusive Volcanism 2. Composite Volcano example: Mt St Helens in 1980

11. 5 Types of Extrusive Volcanism 3. Caldera Volcano
Formed when the upper part of a volcano collapses
The magma chamber below is (partially or completely) emptied after an eruption
The emptied magma chamber can no longer support the weight of the overlying rock
The overlying rock collapses into itself, forming a circular basin
Volcanic activity can continue if there is still magma in the chamber below
Example: Crater Lake, OR

12. 5 Types of Extrusive Volcanism 3
5 Types of Extrusive Volcanism 3. Caldera Volcano example: Crater Lake, OR
Crater Lake was formed after Mt Mazama (a stratovolcano) erupted
and collapsed back in on itself.

13. 5 Types of Extrusive Volcanism 4. Cinder Cones
Smallest mountain formation of all volcanic landform types
Cone-shaped peaks build up from small, solid particles, ejected into air by small volcanic vent
Generally <1,500’ high
Example: Wizard Island

14. 5 Types of Extrusive Volcanism 4
5 Types of Extrusive Volcanism 4. Cinder Cone example: Wizard Island in Crater Lake, OR

15. 5 Types of Extrusive Volcanism 5. Lava Dome
“Plug Dome”
High-silica lava exits from a vent. Due to its high viscosity (doesn’t flow very fast or far), it builds up into a dome.
Effectively “plugs” the main vent. Can still emit ash, gases, and even lava.
Example: Lava Dome in Mt St Helen’s crater.

16. 3 Types of Lava Flows ’A’a Pahoehoe Pillow Lava “Clinky”
Blocky, choppy lava flows that does not flow well over land
Pahoehoe
“Smooth, unbroken lava”
Ropy surface
Pillow Lava
Lava emerges from underwater volcanic vents
Lava cools & crusts when it hits colder water
When crust fractures, lava oozes out and creates billowing pillows

17. ’A’a
Pahoehoe

18. Pillow Lava

19. Dangers of Volcanic Eruptions
Burning Hot Lava
Earthquakes, Landslides and Tsunamis
These are often related – an earthquake might jar some land loose, resulting in a landslide. The earthquake may set off the tsunami. Also, if the landslide falls into the ocean, can trigger a tsunami.
Mudslides (“Lahars”)
Ash Fallout
Pyroclastic Flow (“nuée ardente”)

20. Dangers of Volcanic Eruptions Mudslide (Lahar) examples
Mt. Pinatubo, Philippines
1991 eruption
Mt. St. Helens, WA
1980 eruption

21. Dangers of Volcanic Eruptions Ash fallout example: Mt
Dangers of Volcanic Eruptions Ash fallout example: Mt. Pinatubo, Philippines 1991 eruption

22. Dangers of Volcanic Eruptions Ash fallout example: Mt. St
Dangers of Volcanic Eruptions Ash fallout example: Mt. St. Helens 1980 eruption

23. Dangers of Volcanic Eruptions Pyroclastic flow example: Mt St Helens 1980 eruption
Hot gases, ash, rock that become a “fluid cloud” that move down the side of the volcano. Can travel great distances.
“nuée ardente”: French for “glowing cloud”