VOLCANOES AND VOLCANISM PRODUCTS OF VOLCANISM PYROCLASTIC FLOWS Can have large amounts expelled by volcanoes. Particles are generally large. Gravity tends.

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).

VOLCANOES AND VOLCANISM

PRODUCTS OF VOLCANISM

PYROCLASTIC FLOWSNUÉE ARDENTE

Mt. Pelee,Martinique, 1908

VOLCANOES AND VOLCANISM

PRODUCTS OF VOLCANISM

PYROCLASTIC FLOWSMaterial in nuée ardente may not cool completely

before deposition.Soft material fuses with other particles.Forms solidified tephra.Called WELDED TUFF.

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.

VOLCANOES AND VOLCANISM

PRODUCTS OF VOLCANISM

LAHAR

Mt. Pinatubo, Philippines, 1991

ActiveDormant

Acid rainH2O + SO2 H2SO4 + O2

Climate Influences Dust blocks sunlight.

SO2 reflects and absorb radiation.

1815 - “The Year Without Summer”Eruption of Mt. Tambora, Indonesia

Produced 60-80 mi3 of tephra.

VOLCANOES AND VOLCANISM

PRODUCTS OF VOLCANISM

SECONDARY VOLCANIC AFFECTS

VOLCANOES AND VOLCANISM

PRODUCTS OF VOLCANISM

SECONDARY VOLCANIC AFFECTS

Giant seawavesTSUNAMI are produced by submarine

volcanic eruptions and earthquakes.

VOLCANOES AND VOLCANISM

ERUPTIVE STYLES AND LANDFORMS

Two major features of all volcanoes.

1. VOLCANIC CONE - mountain or hill formed fromsuccessive eruptions.

2. VOLCANIC CRATER - steep-walled bowl-shapeddepression surrounding the vent from which volcanic material escapes.

VOLCANIC CRATER

VOLCANIC CONE

VOLCANOES AND VOLCANISM

Mount Ngauruhoe, NZ

Valley of Fires NationalRecreation Area, NM

VOLCANOES AND VOLCANISM

EFFUSIVE ERUPTIONS

Quiet non-explosive events.Produce basaltic lavas.Small amounts of pyroclastic material is produced.

CENTRAL-VENT ERUPTIONS

VOLCANOES AND VOLCANISM

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 LoaMauna Kea

VOLCANOES AND VOLCANISM

SHIELD VOLCANO

Mauna Loa, HI

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 escapeelsewhere producing a FLANK ERUPTION.

Kilauea on the flank of Mauna Loa, Hawaii.

VOLCANOES AND VOLCANISM

CAULDERA

Kilauea Caldera

VOLCANOES AND VOLCANISM

Kilauea, Hawaii

Flank Volcano

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.

VOLCANOES AND VOLCANISM

Columbia River Plateau lavas, WA.

Deccan Traps, India