1. Introduction to Volcanos
Do not adjust your monitor.

2. Introduction to Volcanos: Outline
Sources of Magma/Lava
Three main sources
Features of Magma/Lava
Mafic, Felsic, Other Components
Effects on Eruptions
Typical Volcanos
Five Representative Kinds

3. Sources of Magma/Lava Convergent Boundaries Divergent Boundaries
IF / ONLY IF OCEANIC CRUST IS SUBDUCTING
Divergent Boundaries
Thinned crust, mantle forms magma
Mantle “Hotspots”
Lava regardless of plate boundaries

4. Sources of Magma/Lava: Convergent Boundaries
Must be subducting oceanic crust
Water encourages rock melt
Does NOT WORK
at continent-continent

5. Sources of Magma/Lava: Divergent Boundaries
Spreading boundaries thin out the crust
Can be cont.-cont. or ocean-ocean
Takes pressure off the mantle
Mantle material melts making magma
Can form new oceanic crust
Can also ERUPT!
Barton beats boredom beneath big blue boundary boxes!

6. Sources of Magma/Lava: Hotspots
Hot liquid mantle rises in a single spot, while plates move over it
Can happen in the middle of a plate!
Competing theories as to why this happens
Ex: Hawai’i chain

7. Getting to Know Your Lava: What to Look For
Is it mafic? (Think dark basalt.)
It will be runny, flows easily
Is it felsic? (Think white rhyolite or pumice.)
It will be VISCOUS, will not easily flow
Can get backed up, build pressure, and explode
Are there complicating factors?
Sea water, glacier, extra dissolved gases

8. Getting to Know Your Lava: How Composition Affects Eruption
Basaltic Lava (Low Viscosity)
Watch:
Typical magma/lava of “hotspots” and some rifts
Rhyolitic Lava (High Viscosity), Presence of Gas
Watch: (Start at about 2:45)
This is an extreme example (“Plinian” eruption)
First vid is Kilauea in Hawai’i, hotspot
Second vid is Vesuvius in Italy, ocean-continent convergence, similar eruption type killed people at Pompeii in 79 CE

9. Some Typical Volcanos Shield Volcano Cinder Cone
Stratovolcano (a.k.a. Composite)
Lava Dome
Caldera

10. Shield Volcano Example – Sierra Grande, NM
Notice very gradual slope, large size
Photo by Joel Barton

11. Shield Volcano Example – Sierra Grande, NM
Notice very gradual slope, large size
Photo by Joel Barton

12. Shield Volcano Example – Mauna Kea, HI
Resembles an ancient shield

13. Cinder Cone Example – Capulin, NM
Exposed scoria in the foreground
Photo by Joel Barton

14. Cinder Cone Example – Capulin, NM
Significantly smaller than Sierra Grande, e.g.
Photo by Joel Barton

15. Cinder Cone Example – Layers of Scoria and Ash, Capulin, NM
Pyroclastic rock – on the boundary of sedimentary and igneous
Photo by Joel Barton

16. Stratovolcano/Composite Basics
Many LAYERS of different erupted material, hence “strato-”

17. Stratovolcano/Composite Example – Mount St. Helens, WA
Left side – day before eruption in 1980
Right side – two years after eruption, notice lava dome in middle

18. Lava Dome Example – Close-up of Mount St. Helens, WA
535 feet high and almost ¼ mile wide, seen from ½ mile away
1 year after 1980 eruption

19. Caldera Basics
Very large, very violent
“Drawing” by Joel Barton

20. Caldera Example – Valle Grande, NM
The entire valley is the caldera crater, and the hills are the rim.
Photo by Joel Barton

21. Caldera Example – Valle Grande, NM
The entire valley is the caldera crater, and the hills are the rim.
Photo by Joel Barton

22. Introduction to Volcanos: Check Yourself
What will the source of the magma help determine?
Why will different lavas erupt differently?
How is the lava/eruption related to the final shape of the volcano?