1. Earth’s Creators and Destroyers
Volcanoes:
Earth’s Creators and Destroyers

2. Where DO Volcanoes occur?
most frequently at plate boundaries
•some occur in the interior of plates at areas called hot spots
•the largest number of volcanoes occur on the ocean floor along spreading ridges
•over 80% of those on land occur at edges of continents, or subduction zones, where one plate dives, or subducts, under another plate

5. How the Earth was Made:Hawaii 11:20 -

6. WHY do volcanoes occur?
temperatures in the mantle are hot enough to melt rock into magma
•less dense than the solid rock around it, magma rises and some of it collects in magma chambers
•as the magma rises, pressure decreases allowing trapped gasses to expand and propel the magma through openings in the Earth’s surface causing an eruption
•erupted magma is called lava

8. eruptions are described as explosive or quiet (loosely flowing)
How DO Volcanoes Erupt ?
eruptions are described as explosive or quiet (loosely flowing)
•how explosive an eruption is depends on the 1)temperature, 2)magma’s chemical composition (silica) and 3)gas content (mostly water vapor), which affect the magma’s stickiness, or viscosity

9. if magma is fluid = gases can escape rapidly and lava flows
if magma is viscous = gases can not escape and pressure builds inside the magma until the gases escape, sometimes violently

10. Other Types of Eruptions
Hot springs and geysers are examples of when groundwater gets heated by the magma Geothermal energy – very useful, clean, energy source

11. Volcano Terms
A vent is an opening through which eruptions take place •A crater is a basin like depression over a vent, at the summit of a volcano •A caldera is a depression larger than the original crater (>1 km. diameter) that forms when the summit is blown off, or when the volcano collapses into the empty magma chamber.

16. Landforms made from LAVA AND ASH
Slow buildup of thin layers of lava – results in mountains with sides that are not steep (quiet eruptions)

17. Cinder Cone LAVA/ash cont.
an explosive eruption’s pyroclastic flow may collect around the vent and produce mountains that have a sharp incline to their slope

18. Composite Volcano – (stratovolcano)
LAVA/ASH cont.
Composite Volcano – (stratovolcano)
Types of eruptions vary therefore this landform is a hybrid of the shield and cinder cone – high elevation and similar cone shape
like a parfait, the layers flip flop between lava and pyroclastic flow

19. ADD FISSURE VOLCANO (Iceland video)
LAVA/ASH
Lava plateau
openings in the crust seep lava (composition classified as quiet lava) – covers large surface area because of its properties – if active for long period of time, can create plateaus
ADD FISSURE VOLCANO (Iceland video)

20. Landforms Made from magma
Volcanic necks – when magma solidifies in the tube within the volcano (pipe) and the outer layers of the volcano erode away Dikes – solidified magma that runs perpendicular to the rock layers Sills – solidified magma that runs parallel to the rock layers

21. MAGMA cont.
Batholith –
upside down bowl shaped mountains formed when magma chambers solidify and layers above and around erode away

22. MAGMA cont.
Dome mountains – similar to batholith except smaller amounts of magma collected underground – forces upper rock layer s to deform and eventually weathers away

38. Monitoring and Predicting Eruptions
Volcanic activity is monitored using several observations:
• land deformation (tiltmeters and laser-ranging devices)
• ash clouds
• tremors measured by seismic data
water volume in crater and overall temperature

39. http://www. youtube. com/watch. v=hmMlspNoZMs http://www. youtube