2. VOLCANOES AND VOLCANISM
PRODUCTS OF VOLCANISM
PYROCLASTIC FLOWS
Can have large amounts expelled by volcanoes.
Particles are generally large.
Gravity tends to pull the pyroclastic material downhill.
PYROCLASTIC FLOW or NUÉE ARDENTE.
Trapped air and magmatic gases keep material
suspended.
Very low friction, velocities >150 km/hr (90 mi/hr).

3. VOLCANOES AND VOLCANISM
PRODUCTS OF VOLCANISM
PYROCLASTIC FLOWS
NUÉE ARDENTE
Mt. Pelee,
Martinique, 1908

5. VOLCANOES AND VOLCANISM
PRODUCTS OF VOLCANISM
PYROCLASTIC FLOWS
Material in nuée ardente may not cool completely
before deposition.
Soft material fuses with other particles.
Forms solidified tephra.
Called WELDED TUFF.

6. VOLCANOES AND VOLCANISM
PRODUCTS OF VOLCANISM
VOLCANIC MUDFLOWS
Pyroclastic material mixes with water.
Flows downhill as a LAHAR.
Generally happens where abundant, loose, moist soil
occurs.
Tropical regions provide this setting.
Helps if volcano is snow-capped or covered with
glaciers.
Ash and dust may actually enhance the potential for
rain.

8. VOLCANOES AND VOLCANISM
PRODUCTS OF VOLCANISM
LAHAR
Mt. Pinatubo, Philippines, 1991

9. Dormant
Active

10. VOLCANOES AND VOLCANISM
PRODUCTS OF VOLCANISM
SECONDARY VOLCANIC AFFECTS
Acid rain
H2O + SO2 H2SO4 + O2
Climate Influences
Dust blocks sunlight.
SO2 reflects and absorb radiation.
“The Year Without Summer”
Eruption of Mt. Tambora, Indonesia
Produced mi3 of tephra.

11. VOLCANOES AND VOLCANISM
PRODUCTS OF VOLCANISM
SECONDARY VOLCANIC AFFECTS
Giant seawaves
TSUNAMI are produced by submarine
volcanic eruptions and earthquakes.

12. VOLCANOES AND VOLCANISM
ERUPTIVE STYLES AND LANDFORMS
Two major features of all volcanoes.
1. VOLCANIC CONE - mountain or hill formed from
successive eruptions.
2. VOLCANIC CRATER - steep-walled bowl-shaped
depression surrounding the vent from which
volcanic material escapes.

13. VOLCANOES AND VOLCANISM
VOLCANIC CONE
Mount Ngauruhoe, NZ
VOLCANIC CRATER
Valley of Fires National
Recreation Area, NM

14. VOLCANOES AND VOLCANISM
EFFUSIVE ERUPTIONS
Quiet non-explosive events.
Produce basaltic lavas.
Small amounts of pyroclastic material is produced.

15. VOLCANOES AND VOLCANISM
CENTRAL-VENT ERUPTIONS
Basaltic lava flows from one vent.
Flows out evenly in all directions.
Produces a low, broad volcanic cone.
Termed a SHIELD VOLCANO.
Gentle slope with a broad summit.
Found in Hawaii: Mauna Loa
Mauna Kea

16. VOLCANOES AND VOLCANISM
SHIELD VOLCANO
Mauna Loa, HI

17. VOLCANOES AND VOLCANISM
Lava may accumulate in the crater of the volcano.
Crater fills to capacity and flows over the edge.
Summit may then collapse into the evacuated area.
Produces a CALDERA.
CALDERA are typically big.
Collapse may close the vent causing lava to escape
elsewhere producing a FLANK ERUPTION.
Kilauea on the flank of Mauna Loa, Hawaii.

18. VOLCANOES AND VOLCANISM
CAULDERA
Kilauea Caldera

19. VOLCANOES AND VOLCANISM
Kilauea, Hawaii
Flank Volcano

20. VOLCANOES AND VOLCANISM
FISSURE ERUPTIONS ON LAND
Series of linear fractures or fissures.
Produces FLOOD BASALTS.
Lava spreads out in thick layers.
Thick layers are called LAVA PLATEAUS.

21. VOLCANOES AND VOLCANISM
Columbia River Plateau lavas, WA.

22. Deccan Traps, India