Download Mantle Plumes and Hot

Yellowstone NP: Volcanoes and Geysers
• Yellowstone is at
the ‘tip’ of the
Snake River Plane
• Teton NP is just to
the South
• Notice also the
Columbia River
Plateau
• Using Yellowstone, we will review mantle plumes (hot spots) and
discuss: mantle melting, magmatic-volcanic systems, Geologic
history of Yellowstone and Hydrothermal systems such as geysers
and hot springs.
Mantle Plumes and Hot-Spots
• Mantle Plume = anomalously hot
mantle rising from depth
• Rising plume melts to produce
volcanoes on the surface (= a hot spot)
– A hot-spot track results from the
lithosphere moving over the plume
Draw decompressive melting
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Magmatic-Volcanic System
• Extrusive or Volcanic
system
– Volcano,
– lava (magma extruded
on the surface),
– and ash or pyroclastic
material
• Intrusive or magmatic
system
– Magma chamber stores
magma (mixture of
liquid and crystals)
– Fed with melt from the
mantle
– Rocks from this system
cool deep in earth
(slowly) and grow
• Hypabyssal Rocks = shallow intrusive rocks.
large crystals
Dikes and sills
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Volcano Locations and Tectonic Setting
•MOR system: 65,000 km long, erupts > 10 km3 of lava per year
•Subduction zones: ‘Typical’ shape, Hazardous, Historic: Tambora (1815),
Krakatau (1883), Vesuvius (79 AD Pompeii), Mt St Helens (1980) , Pinatubo (1991), Montserrat
•Intraplate: Hot-spots or plumes, few in number
Shield Volcanoes
•Size: 10s - 100s km diameter, 1-10 km high (HUGE)
•Shape: circular, oval, and ‘linear’
•Composed of layers of lava
•Tectonic Setting: Divergent (MOR & Rifts) and intraplate
•Largest volcanoes on Earth and in Solar System
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Examples of Shield Volcanoes
Examples of Shield Volcanoes
Mauna Kea
Mauna Loa
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Shield Eruptions: gentle fissure eruptions
Krafla Iceland
Hawaii
Shield Eruptions: gentle fissure eruptions
Hawaii
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Stratovolcanoes
•Size: 1-10 km diameter, < 5 km tall
•Shape: Classic conical shape (Think Fuji)
•Composed of ash with interlayered lava
•Tectonic setting: Subduction zones
•Hazardous volcanoes
Example Stratovolcanoes
Shasta
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Cinder Cones
Sunset Craters
•Small: <km diameter, 100s m tall
•Composed of cinders and blocks ejected from vent
Relative Sizes
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Caldera Collapse
• Inflated magma chamber
lifts and cracks the
overlying crust.
• Magma erupts out this ringfissure system
• Decompression of the
magma chamber causes
gasses to exsolve (bubbles)
pushing more magma out
the fissures.
• Roof collapse pushes even
more magma out.
• These are huge eruptions!
• 100s to 1000s km3 of
magma
Geologic History of Yellowstone area
• Basement is old
Precambrian metamorphic
rocks similar to Yavapai
province
• Covered with thick
Paleozoic and Mesozoic
sediments from repeated
transgressions and
regressions.
– >9000’ total
– Must have been a stable
basin to collect so much
sediment.
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Geologic History of Yellowstone area
• Laramide Orogeny uplifted portions of the area
– Small basins filled with sediment from uplifted regions
• Absaroka Volcanic Supergroup
– Derived from volcanoes east of Yellowstone area
– Covered Yellowstone area in ~10,000’ of basalt and
ash (some dikes too).
~ 5 Ma Basin and Range extension of North America
• This raised
Yellowstone area and
the Tetons
• Lowered Jackson Hole
• Continues today
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Volcanic History of Yellowstone
• Columbia River Flood Basalts ~20 to 15 Ma
• Snake River Plane = track of Yellowstone Hotspot.
• Arrives at Yellowstone ~2 Ma
Island Park Caldera
• 2 Ma Collapse produced
the Island Park Caldera
– 30x50 Mi
– Erupted the Huckleberry
Ridge Tuff
• Smaller 1.3 Ma event
erupted the Mesa Falls
Tuff
• At 1.2 Ma the system
shifted to Yellowstone
Caldera
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Huge 0.63 Ma event at Yellowstone Caldera
• Catastrophic eruption of
>1000 km3 of magma
– Covered mid-continent of
NA with ash (Lava Creek
Tuff)
– Caldera = 45 x 25 x0.5
miles
• Resurgent domes (two) in
Yellowstone Caldera
indicates future activity.
Hydrothermal Activity at Yellowstone:
Geysers and Hot Springs
Mammoth Hot Spring
Castle Geyser
• Groundwater flows through the
rocks and is heated by magma
chamber.
• Chemically weathers the rocks it
flows through and precipitates
minerals on the surface.
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Hot Springs: Paint Pots & Mud Pots
• Paint Pot:
Chemotrophic
Archeobacteria living
in the boiling hot
water give it color.
• Mud Pots = spring
water mixes with
volcanic clays
(bentonite)
Geyser = eruption of hot spring
• Water flows into and fills
a conduit/cavern system
• Groundwater Heated with
heat from the magma
chamber
• Deep in the conduit, water
is under pressure (high
boiling point)
• Shallow water eventually
boils and evacuates the
conduit
• This releases pressure on
the deep portions of the
conduit and they FLASH
to steam (eruption).
Old Faithful
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Old Faithful
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