1. Volcanoes What is a Volcanism & volcano? Nature & origin of volcano
Causes of volcanism
Products of volcanism
types of Volcanoes
Benefits

2. What is a volcanism & volcano ?
A volcano is an opening, or rupture, in the surface or crust of the Earth or a planetary mass object, which allows hot lava, volcanic ash and gases to escape from the magma chamber below the surface.

3. Where do volcanoes erupt?
A) In the middle of the earth’s plates, hotspots.
B) Near the edges of the earth’s plates.
C) Subduction and rift zones.

4. Volcanoes result from magma rising off the melting subducted plate.

5. Oceanic Ridge Volcanoes.

6. Nature & origin of volcano
Active volcano
Dormant volcano
Extinct volcano

7. Active volcano
Currently erupting
Recently erupted
10,000 years

8. Dormant volcano Not erupted recently but in future
Increasing earth temp.

9. Extinct volcano Erupted long time ago Unlikely to erupt again
Massive erosion

10. Causes of volcanism
Gas in volcanic magma
Magma viscosity

11. Why do volcanoes erupt?
Hot, melted rock (magma) deep within the earth becomes lighter as it heats up. Because it is lighter than solid rock it rises until it pushes to the surface of the earth. A volcanic eruption occurs!

12. Gas & magma viscosity 1% to 9% Decrease in pressure
Increase in Viscosity
Felsic (silica & low cooling temp)
Mefic (low viscosity & high temp)
High viscosity & more pressure

13. Products of volcanism Types of lava Basaltic lava Andesite lava
Rhyolitic lava

14. Basaltic lava Low viscosity & temp. Pahoehoe(high speed & thin sheet )
Aa( cooler material inside & hot material outside)
Scoria & columnar jointing (shrinkage )
Lava tubes

15. Pahoehoe: Lava with a ropelike surface texture due to partial cooling as the lava flowed. Relatively hot, low viscosity lava.

16. Aa: Blocky, rough lava flow
Aa: Blocky, rough lava flow. Due to high viscosity lava that flowed pushing chunks of solid and semi-solid blocks.

17. Lava tube: A tube formed by cooling and solidifying of the lava walls while fluid lava continued to flow inside.

18. Andesite lava
Intermediate flow
Near to vent
Scoria but less sheets

19. Rhyolitic lava High viscosity Mostly Cools with earth
Explosive at earth
Pumice

20. Pyroclasts & tephra Fire fragments Cooling in air
Volcanic dust (1000th of milimeter ),volcanic ash (less than 2 mm)
Cinders (2 to 64mm)
Volcani boomb (more than 64mm)
Volcanic tuff (cemented)

21. Ash: tephra that is finer than 2 mm in diameter.

22. Lapilli: from 2 mm to 64 mm in diameter.
Blocks: hard fragments greater than 64 mm in diameter.

23. Bombs: soft, partially melted fragments greater than 64 mm in diameter.

24. Volcanic mud flows Mixing with water (lahar )
Finest ash to 100 ton boulders
Near ice &High speeds

25. Landforms Volcanic cone & crater
Effusive eruption (quiet ,non explosive eruptions)
Caldera (a depression )
Fissuries eruptions
Subaqueous eruptions (quiet & effusive)
Pyroclatic (gass rich,explosives)
Volcanic dome (felsic material)
Culminating eruption (highly explosive ,caldera)
Ash flow eruptions

26. Types of volcnos
Shield volcano
Composite
Cinder cone

27. Shield volcanoes: dominated by lava flows.
Muana Loa Volcano – the world’s largest volcano.

28. Typical slopes approximately 15 degrees.
Lava flows downslope, away from a central vent or a series of vents. Low viscosity lava forms fountains of lava flowing from vents near the volcano summit. The lava flows easily down the gentle slopes….reaching the ocean during some eruptions.
USGS

29. Cinder cones: dominated by pyroclastics.
Forms an isolated conical mound of tephra.
Photograph by J.P. Lockwood on 1 December 1975

30. Internally constructed entirely of layers of pyroclastic deposits (blocks, bombs, lapilli). Typical angles: 30 to 40 degrees
Slopes are steep, at angle of repose.
Angle of repose: the natural maximum angle that a pile of loose, unconsolidated material will form.

31. Stratovolcanoes: mixture of lavas and pyroclastics.

32. Steep slopes, at angle of repose or greater.
Stratovolcanoes
© Noemi Emmelheinz 2001
Volcanoes that alternate between periods of lava flows (constructive phase) and periods of explosive eruptions (destructive phase).
Commonly called “composite volcanoes” because they are made up of both lava and pyroclastic deposits.
Steep slopes, at angle of repose or greater.

33. Benefits of volcanoes Eruption of gases Information of interor
Equilibrium
Geothermal heat