PRODUCTS OF VOLCANISM

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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 gt150 km/hr (90 mi/hr).
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PRODUCTS OF VOLCANISM
PYROCLASTIC FLOWS
NUÉE ARDENTE
Mt. Pelee, Martinique, 1908
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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.
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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.
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PRODUCTS OF VOLCANISM
LAHAR
Mt. Pinatubo, Philippines, 1991
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Active
Dormant
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PRODUCTS OF VOLCANISM
SECONDARY VOLCANIC AFFECTS
Acid rain H2O 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.
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PRODUCTS OF VOLCANISM
SECONDARY VOLCANIC AFFECTS
Giant seawaves TSUNAMI are produced by
submarine volcanic eruptions and earthquakes.
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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.
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VOLCANIC CONE
Mount Ngauruhoe, NZ
VOLCANIC CRATER
Valley of Fires National Recreation Area, NM
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EFFUSIVE ERUPTIONS
Quiet non-explosive events. Produce basaltic
lavas. Small amounts of pyroclastic material is
produced.
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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
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SHIELD VOLCANO
Mauna Loa, HI
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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.
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CAULDERA
Kilauea Caldera
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Kilauea, Hawaii
Flank Volcano
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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.
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Columbia River Plateau lavas, WA.
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Deccan Traps, India