Download Typical shield volcano Mauna Loa, Hawaii

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Igneous Forms
• Intrusive
• Extrusive
Types of volcanoes
• Shield volcano
– Broad, slightly domed-shaped
– Produced by mild eruptions of large volumes of lava
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Types of volcanoes
• Shield volcano
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Broad, slightly domed-shaped
Produced by mild eruptions of large volumes of lava
primarily basaltic
Example: Mauna Loa on Hawaii
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Typical shield volcano
Mauna Loa, Hawaii
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Where?
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Types of volcanoes
– Cinder cone
–ejected lava fragments
–Steep slope angle
–small
–occur in groups
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Diagram of Cinder Cone
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Types of volcanoes
Sunset Crater – a cinder cone near Flagstaff, Arizona
– Composite volcano (Stratovolcano)
– Large, classic-shaped volcano
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Distribution of some of the world’
world’s major volcanoes
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Types of volcanoes
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– Composite volcano (Stratovolcano)
– Large, classic-shaped volcano
– Most located adjacent to the Pacific Ocean
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Types of volcanoes
– Composite volcano (Stratovolcano)
– Large, classic-shaped volcano
– Most located adjacent to the Pacific Ocean
– Interbedded lava flows and layers of pyroclastic debris
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A composite (strato
(strato)) volcano
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Mt. St. Helens – a typical composite volcano
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Mt. St. Helens following the eruption
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Mt. St. Helens following the 1980 eruption
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Diagram of the eruption of Mt. St.Helens
St. Pierre as it appeared shortly after the eruption of Mt.
Pelee,
Pelee, Martinique
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Relationships among magma types / appearances and volcanic eruption
/ landform types
A size comparison of the three types of volcanoes
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Composite volcanoes
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– Most violent type
– Often produce a nueé ardente.
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Composite volcanoes
– Most violent type
– Often produce a nueé ardente. Fiery pyroclastic flow of
hot gases infused with ash and other debris
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Composite volcanoes
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– Most violent type
– Often produce a nueé ardente. Fiery pyroclastic flow of
hot gases infused with ash and other debris
– May produce a lahar, a volcanic mudflow
A nueé
nueé ardente on Mt. St. Helens
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Fissure eruptions and lava plateaus
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Basaltic Fissure Eruption – Fig. 4.25
Lava flows - picture
Columnar jointing of lava flow
Columnar jointing of lava flow - picture
Columnar jointing – Giants Causeway, Ireland, Fig. 4.31
Columnar jointing of basalt
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Other volcanic landforms
• Lava Domes
• Volcanic pipes and necks
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Lava Domes
example: inside Mt. St. Helens
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Formation of a volcanic neck
Shiprock, NM – a volcanic neck
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Devils Tower, Wyoming:
A Volcanic Neck
Photo by NDSU Geology Major, Julia Karst-Gray
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Intrusive igneous structures
Plutons
• Most magma is emplaced at depth
• An solidified underground igneous body = a pluton
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Classification of plutons
• Pluton orientation with respect to the host (surrounding) rock
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Classification of plutons
• Pluton orientation with respect to the host (surrounding) rock
– Discordant – cuts across pre-existing units
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Classification of plutons
• Pluton orientation with respect to the host (surrounding) rock
– Discordant – cuts across pre-existing units
– Concordant – parallel to pre-existing units
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Plutonic igneous activity
• Types of intrusive igneous features
• Dike – a tabular, discordant pluton
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-example: near Duluth, Minnesota
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Dike near Duluth Minnesota
Plutonic igneous activity
• Types of intrusive igneous features
• Sill – a tabular, concordant pluton
• - example in Ontario
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Diagram showing formation of igneous landforms
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A sill in the Salt River Canyon, Arizona
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Batholiths
Largest intrusive body
–Surface exposure > 100 km2 (smaller bodies =
stocks)
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Batholiths
Largest intrusive body
–Surface exposure > 100 km2 (smaller bodies =
stocks)
–Usually felsic; form the cores of mountains
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Batholiths of western North America
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Plastic deformation of country rock at margins of
intrusion – brittle deformation at higher levels
Erosion to expose intrusive rocks – Fig. 4.28
Uplift and erosion – Fig. 4.28
Picture of exposed batholith
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Sierra Nevada Batholith, California
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Interaction of magma with country rock:
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fracturing, dislodging of country rock = stoping
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Inclusions of country rock=
xenoliths
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Xenolith in granite near Mount Rushmore, South Dakota
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