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Home , Shield volcano, Volcano

1 Igneous Forms • Intrusive • Extrusive 2 Types of volcanoes • Shield – Broad, slightly domed-shaped – Produced by mild eruptions of large volumes of

3 Types of volcanoes • – Broad, slightly domed-shaped – Produced by mild eruptions of large volumes of lava – primarily basaltic – Example: on

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7 Typical shield volcano 8 Mauna Loa, Hawaii 9 Where? 10 Types of volcanoes – –ejected lava fragments –Steep slope angle –small –occur in groups 11 Diagram of Cinder Cone 12 – a cinder cone near Flagstaff, 13 Types of volcanoes –Composite volcano () – 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

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 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, 23 Relationships among types / appearances and volcanic eruption / 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 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 , a volcanic mudflow 28 A nueé ardente on Mt. St. Helens 29 Fissure eruptions and lava

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 36 Other volcanic • 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 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 • – a tabular, discordant pluton

3 -example: near Duluth,

48 Dike near Duluth Minnesota 49 Plutonic igneous activity • Types of intrusive igneous features • – a tabular, concordant pluton • - example in Ontario 50 Diagram showing formation of igneous landforms 51 A sill in the Salt River Canyon, Arizona 52 Largest intrusive body –Surface exposure > 100 km2 (smaller bodies = stocks)

53 Batholiths Largest intrusive body –Surface exposure > 100 km2 (smaller bodies = stocks)

–Usually ; form the cores of

54 Batholiths of western 55 Plastic deformation of 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 59 Sierra Nevada Batholith, 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

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