1. Chapter 7
Sections 3 & 4
volcanoes

2. Volcanic Eruptions
As magma heats up it becomes LESS dense and flows upwards.
If there is an opening in the crust, it will reach the earth’s surface – a volcano is born!

3. Inside a volcano

5. ERUPTIONS
As magma rises the pressure surrounding it decreases. (It is not as deep anymore) This allows gases in and around the magma to expand. These expanding gases push the magma out of the volcano.
Eruptions can spew out
Ash – fine dust specks
Cinders – pebble-sized particles
Bombs – baseball to car sized
pieces!

6. CINDERS
ASH
BOMBS!

7. 2 types of eruptions
QUIET: magma low in silica; magma flows easily, gases bubble out slowly and gently.
EXPLOSIVE: magma high in silica; thick/sticky; doesn’t always flow out of the crater; can plug it like a cork; gases get trapped and build up pressure until they “explode”.
PYROCLASTIC FLOW: when the volcano hurls out a mixture of hot gases, ash, cinders, and bombs.

8. QUIET
EXPLOSIVE

9. SCARY PYROCLASTIC FLOW!
Mt. Pinatubo
Philippines
1991 eruption

10. More pyroclastic flows

11. Edge of a pyroclastic flow

12. Pyroclastic flows cause tremendous damage!

13. Volcano Hazards Fire Ash can bury towns Landslides Mudslides
Flooding (melted snow)

14. Stages of Volcanic Activity
Volcanoes are classified
as:
ACTIVE – a live volcano that is erupting or will in the near future
DORMANT – “sleeping” may erupt again
EXTINCT – a dead volcano; unlikely to ever erupt again.

15. TYPES OF VOLCANOES
Wide, gently sloping, usually form at a hot spot, lava pours out gently
Lava has high viscosity, steep, cone shaped hill, more explosive eruptions
Combination of both; sometimes gently flowing lava, sometimes explosive, alternating layers of ash/cinders & lava

16. Click for the video clip!

17. Other volcanic landforms
Lava plateau – lava flows out of several long cracks in an area and eventually over hundreds of years build up to form a plateau

18. Calderas
Caldera – huge hole left by the collapse of volcano

19. Soils from Lava & Ash
When hardened lava erodes and forms soil, phosphorous, potassium and other important minerals are released. These make the soil very fertile.

20. Dikes and Sills
When magma forces itself across rock layers it hardens into a DIKE. When magma squeezes between horizontal layers of rock it forms a SILL.

22. Dikes & Sills in New Zealand

23. Volcanic Necks
Forms when magma hardens in the volcano’s pipe and the softer rock surrounding it erodes away.

24. Batholiths & Dome Mountains
Batholith: large rock masses form the core of many mtn ranges; formed when a large body of magma cools inside the crust.
Dome Mountain: smaller bodies of hardened magma

25. Sierra Batholith (Yosemite Nat’l Park)
Batholiths
Sierra Batholith (Yosemite Nat’l Park)

26. Dome Mountains

27. Geothermal Activity Geo – means “earth” Therme – means “heat”
Geothermal is heat produced by the Earth (actually magma!)
Hot springs & Geysers are types of geothermal activity found in volcanic areas.

28. In ARKANSAS
In IDAHO
Hot Springs

29. GEYSERS (New Zealand)