1. Volcanoes

2. Magma
Is a mixture of molten rock, suspended mineral grains and dissolved gasses
Formed when temperatures become high enough to melt rock
Most rocks begin to melt around
1472 degrees F to 2192 degrees F
800 degrees C to 1200 degrees F

3. Magma Where the lithosphere and asthenosphere meet, it gets this hot
It is at the flexible plastic-like layer of the lithosphere.

8. Shield, Cinder and Composite
Types of Volcanoes
Shield, Cinder and Composite

9. Shield Volcano

11. Shield Volcanoes Low viscosity lava flows Low silica magma (mafic)
Basalt – 2 types:
pahoehoe-having a smooth or billowy surface.
A’a’-most common appearance type of lava flows that cool down forming fragmented, rough, sometimes spiny

12. Shield Volcanoes Gently sloping sides (known as flanks)
Tend to be very large
Circular at the base
Spatter cone is a minor feature

16. Cinder Cone Volcano

18. Cinder Cone Steep sides (flanks) Large amounts of silica = thick lava
More water, silica and gasses than Shield Volcanoes
Because more gasses = more explosive
Thick lava gets stuck in the caldera
When the pressure builds, it pops the cork and explodes
Material ejected high into the sky
Short duration – Once it explodes, then it’s over

21. Composite Volcano

23. Composite Form when runny lava escapes through a fissure and flows out
Tall cone-shaped mountains that are typically steeply-sided, symmetrical cones of large dimensions
The essential feature of a composite volcano is a conduit system through which magma from a reservoir deep in the earth's crust rises to the surface.
Erupt in different ways at different times.

24. Composite
Most composite volcanoes have a crater at the summit which contains a central vent or a clustered group of vents.
Lava either flow through breaks in the crater wall or from fissures on the flanks of the cone.
Some composite volcanoes occur in chains. There are many composite volcano chains on earth, notably around the Pacific Rim, known as the "Rim of Fire”

29. Mt. St. Helens

30. Mt St. Helens - Before

31. Mt St. Helens – After

33. Before

34. After

39. Mt. St. Helens - Before

40. Mt. St. Helens - After