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Typical Shield Volcano Mauna Loa, Hawaii

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Typical Shield Volcano Mauna Loa, Hawaii 1 Igneous Forms • Intrusive • Extrusive 2 Types of volcanoes • Shield volcano – Broad, slightly domed-shaped – Produced by mild eruptions of large volumes of lava 3 Types of volcanoes • Shield volcano – Broad, slightly domed-shaped – Produced by mild eruptions of large volumes of lava – primarily basaltic – Example: Mauna Loa on Hawaii 4 5 6 7 Typical shield volcano 8 Mauna Loa, Hawaii 9 Where? 10 Types of volcanoes – Cinder cone –ejected lava fragments –Steep slope angle –small –occur in groups 11 Diagram of Cinder Cone 12 Sunset Crater – a cinder cone near Flagstaff, Arizona 13 Types of volcanoes –Composite volcano (Stratovolcano) – Large, classic-shaped volcano 14 Distribution of some of the world’s major volcanoes 15 Types of volcanoes 1 –Composite volcano (Stratovolcano) – Large, classic-shaped volcano – Most located adjacent to the Pacific Ocean 16 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 17 A composite (strato) volcano 18 Mt. St. Helens – a typical composite volcano 19 Mt. St. Helens following the eruption 20 Mt. St. Helens following the 1980 eruption 21 Diagram of the eruption of Mt. St.Helens 22 St. Pierre as it appeared shortly after the eruption of Mt. Pelee, Martinique 23 Relationships among magma types / appearances and volcanic eruption / landform types 24 A size comparison of the three types of volcanoes 25 Composite volcanoes –Most violent type –Often produce a nueé ardente. 26 Composite volcanoes –Most violent type –Often produce a nueé ardente. Fiery pyroclastic flow of hot gases infused with ash and other debris 27 Composite volcanoes –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 28 A nueé ardente on Mt. St. Helens 29 Fissure eruptions and lava plateaus 2 30 Basaltic Fissure Eruption – Fig. 4.25 31 Lava flows - picture 32 Columnar jointing of lava flow 33 Columnar jointing of lava flow - picture 34 Columnar jointing – Giants Causeway, Ireland, Fig. 4.31 35 Columnar jointing of basalt 36 Other volcanic landforms • Lava Domes • Volcanic pipes and necks 37 Lava Domes example: inside Mt. St. Helens 38 Formation of a volcanic neck 39 Shiprock, NM – a volcanic neck 40 41 Devils Tower, Wyoming: A Volcanic Neck Photo by NDSU Geology Major, Julia Karst-Gray 42 Intrusive igneous structures 43 Plutons • Most magma is emplaced at depth • An solidified underground igneous body = a pluton 44 Classification of plutons • Pluton orientation with respect to the host (surrounding) rock 45 Classification of plutons • Pluton orientation with respect to the host (surrounding) rock – Discordant – cuts across pre-existing units 46 Classification of plutons • Pluton orientation with respect to the host (surrounding) rock – Discordant – cuts across pre-existing units – Concordant – parallel to pre-existing units 47 Plutonic igneous activity • Types of intrusive igneous features • Dike – a tabular, discordant pluton 3 -example: near Duluth, Minnesota 48 Dike near Duluth Minnesota 49 Plutonic igneous activity • Types of intrusive igneous features • Sill – a tabular, concordant pluton • - example in Ontario 50 Diagram showing formation of igneous landforms 51 A sill in the Salt River Canyon, Arizona 52 Batholiths Largest intrusive body –Surface exposure > 100 km2 (smaller bodies = stocks) 53 Batholiths Largest intrusive body –Surface exposure > 100 km2 (smaller bodies = stocks) –Usually felsic; form the cores of mountains 54 Batholiths of western North America 55 Plastic deformation of country rock at margins of intrusion – brittle deformation at higher levels 56 Erosion to expose intrusive rocks – Fig. 4.28 57 Uplift and erosion – Fig. 4.28 58 Picture of exposed batholith 59 Sierra Nevada Batholith, California 60 Interaction of magma with country rock: fracturing, dislodging of country rock = stoping 4 Inclusions of country rock= xenoliths 61 Xenolith in granite near Mount Rushmore, South Dakota 5.
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