![Page 1: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/1.jpg)
Earth Science, Earth Science, 12e12e
Volcanoes and Other Volcanoes and Other Igneous ActivityIgneous Activity
Chapter 9Chapter 9
![Page 2: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/2.jpg)
Volcanic eruptions Volcanic eruptions
Factors that determine the violence of an eruption • Composition of the magma • Temperature of the magma• Dissolved gases in the magma
Viscosity of magma • Viscosity is a measure of a material’s
resistance to flow
![Page 3: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/3.jpg)
Volcanic eruptions Volcanic eruptions
Viscosity of magma • Factors affecting viscosity
• Temperature (hotter magmas are less viscous) • Composition (silica content)
• High silica – high viscosity (e.g., rhyolitic lava)
• Low silica – more fluid (e.g., basaltic lava)• Dissolved gases (volatiles)
• Mainly water vapor and carbon dioxide • Gases expand near the surface
![Page 4: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/4.jpg)
Volcanic eruptions Volcanic eruptions
Viscosity of magma • Factors affecting viscosity
• Dissolved gases (volatiles) • Provide the force to extrude lava • Violence of an eruption is related to how
easily gases escape from magma • Easy escape from fluid magma • Viscous magma produces a more violent
eruption
![Page 5: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/5.jpg)
Materials associated with Materials associated with volcanic eruptions volcanic eruptions
Lava flows • Basaltic lavas are more fluid• Types of lava
• Pahoehoe lava (resembles braids in ropes) • Aa lava (rough, jagged blocks)
Gases • One to five percent of magma by weight• Mainly water vapor and carbon dioxide
![Page 6: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/6.jpg)
A pahoehoe lava flowA pahoehoe lava flow
Figure 9.7 B
![Page 7: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/7.jpg)
A typical aa flowA typical aa flow
Figure 9.7 A
![Page 8: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/8.jpg)
Materials associated with Materials associated with volcanic eruptions volcanic eruptions
Pyroclastic materials • “Fire fragments” • Types of pyroclastic material
• Ash and dust – fine, glassy fragments • Pumice – from “frothy” lava • Lapilli – “walnut” size • Cinders – “pea-sized” • Particles larger than lapilli
• Blocks – hardened lava • Bombs – ejected as hot lava
![Page 9: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/9.jpg)
Volcanic bombs on Volcanic bombs on Kilauea volcano in HawaiiKilauea volcano in Hawaii
Figure 9.9
![Page 10: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/10.jpg)
Volcanoes Volcanoes
General features • Conduit, or pipe, carries gas-rich magma to
the surface • Vent, the surface opening (connected to
the magma chamber via a pipe) • Crater
• Steep-walled depression at the summit • Caldera (a summit depression greater than 1
km diameter)
![Page 11: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/11.jpg)
Volcanoes Volcanoes General features
• Parasitic cones • Fumaroles
Types of volcanoes • Shield volcano
• Broad, slightly domed • Primarily made of basaltic (fluid) lava • Generally large size • e.g., Mauna Loa in Hawaii
![Page 12: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/12.jpg)
Shield volcanoShield volcano
Figure 9.12
![Page 13: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/13.jpg)
Volcanoes Volcanoes
Types of volcanoes • Cinder cone
• Built from ejected lava fragments • Steep slope angle • Rather small size • Frequently occur in groups
![Page 14: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/14.jpg)
A cinder cone near A cinder cone near Flagstaff, ArizonaFlagstaff, Arizona
Figure 9.15
![Page 15: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/15.jpg)
Volcanoes Volcanoes
Types of volcanoes • Composite cone (or stratovolcano)
• Most are adjacent to the Pacific Ocean (e.g., Mt. Rainier)
• Large size • Interbedded lavas and pyroclastics • Most violent type of activity
![Page 16: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/16.jpg)
Composite volcano Composite volcano
Figure 9.10
![Page 17: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/17.jpg)
Mount St. Helens – a typical Mount St. Helens – a typical composite volcanocomposite volcano
![Page 18: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/18.jpg)
Mount St. Helens following Mount St. Helens following the 1980 eruptionthe 1980 eruption
![Page 19: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/19.jpg)
A size comparison of the A size comparison of the three types of volcanoesthree types of volcanoes
Figure 9.13
![Page 20: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/20.jpg)
Volcanoes Volcanoes
Types of volcanoes • Composite cone (or stratovolcano)
• Often produce nuée ardente • Fiery pyroclastic flow made of hot gases
infused with ash • Flows down sides of a volcano at speeds up
to 200 km (125 miles) per hour• May produce a lahar – volcanic mudflow
![Page 21: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/21.jpg)
A nuA nuééee ardente on ardente on Mount St. HelensMount St. Helens
Figure 9.18
![Page 22: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/22.jpg)
A lahar along the Toutle A lahar along the Toutle River near Mount St. HelensRiver near Mount St. Helens
Figure 9.20
![Page 23: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/23.jpg)
Other volcanic landforms Other volcanic landforms
Calderas • Steep-walled depression at the summit • Formed by collapse • Nearly circular • Size exceeds 1 kilometer in diameter
Fissure eruptions and lava plateaus • Fluid basaltic lava extruded from crustal
fractures called fissures • e.g., Columbia Plateau
![Page 24: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/24.jpg)
Crater Lake, Crater Lake, Oregon, is a Oregon, is a
good example good example of a calderaof a caldera
Figure 9.21
![Page 25: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/25.jpg)
The Columbia River basaltsThe Columbia River basalts
Figure 9.22
![Page 26: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/26.jpg)
Other volcanic landforms Other volcanic landforms
Volcanic pipes and necks • Pipes are short conduits that connect a
magma chamber to the surface • Volcanic necks (e.g., Ship Rock, New
Mexico) are resistant vents left standing after erosion has removed the volcanic cone
![Page 27: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/27.jpg)
Formation of a Formation of a volcanic neckvolcanic neck
Figure 9.24
![Page 28: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/28.jpg)
Intrusive igneous activity Intrusive igneous activity
Most magma is emplaced at depthAn underground igneous body is called
a plutonPlutons are classified according to
• Shape• Tabular (sheetlike)• Massive
![Page 29: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/29.jpg)
Intrusive igneous activity Intrusive igneous activity
Plutons are classified according to • Orientation with respect to the host
(surrounding) rock • Discordant – cuts across existing structures • Concordant – parallel to features such as
sedimentary strata
![Page 30: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/30.jpg)
Intrusive igneous activity Intrusive igneous activity
Types of igneous intrusive features • Dike, a tabular, discordant pluton • Sill, a tabular, concordant pluton
• e.g., Palisades Sill, NY • Resemble buried lava flows • May exhibit columnar joints
• Laccolith • Similar to a sill
![Page 31: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/31.jpg)
Intrusive igneous structuresIntrusive igneous structures exposed by erosion exposed by erosion
Figure 9.25 B
![Page 32: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/32.jpg)
A sill in the Salt River A sill in the Salt River Canyon, Arizona Canyon, Arizona
Figure 9.27
![Page 33: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/33.jpg)
Intrusive igneous activity Intrusive igneous activity
Types of igneous intrusive features • Laccolith
• Lens-shaped mass • Arches overlying strata upward
• Batholith• Largest intrusive body • Often occur in groups • Surface exposure 100+ square kilometers
(smaller bodies are termed stocks) • Frequently form the cores of mountains
![Page 34: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/34.jpg)
A batholith exposed A batholith exposed by erosionby erosion
Figure 9.25 C
![Page 35: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/35.jpg)
Origin of magma Origin of magma
Magma originates when essentially solid rock, located in the crust and upper mantle, melts
Factors that influence the generation of magma from solid rock • Role of heat
• Earth’s natural temperature increases with depth (geothermal gradient) is not sufficient to melt rock at the lower crust and upper mantle
![Page 36: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/36.jpg)
Origin of magma Origin of magma
Factors that influence the generation of magma from solid rock • Role of heat
• Additional heat is generated by • Friction in subduction zones• Crustal rocks heated during subduction • Rising, hot mantle rocks
![Page 37: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/37.jpg)
Origin of magma Origin of magma
Factors that influence the generation of magma from solid rock • Role of pressure
• Increase in confining pressure causes an increase in melting temperature
• Drop in confining pressure can cause decompression melting
• Lowers the melting temperature • Occurs when rock ascends
![Page 38: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/38.jpg)
Origin of magma Origin of magma
Factors that influence the generation of magma from solid rock • Role of volatiles
• Primarily water• Cause rock to melt at a lower temperature • Play an important role in subducting ocean
plates
![Page 39: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/39.jpg)
Origin of magma Origin of magma
Factors that influence the generation of magma from solid rock • Partial melting
• Igneous rocks are mixtures of minerals • Melting occurs over a range of temperatures • Produces a magma with a higher silica content
than the original rock
![Page 40: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/40.jpg)
Plate tectonics and Plate tectonics and igneous activity igneous activity
Global distribution of igneous activity is not random • Most volcanoes are located on the margins
of the ocean basins (intermediate, andesitic composition)
• Second group is confined to the deep ocean basins (basaltic lavas)
• Third group includes those found in the interiors of continents
![Page 41: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/41.jpg)
Locations of some of Locations of some of Earth’s major volcanoesEarth’s major volcanoes
Figure 9.33
![Page 42: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/42.jpg)
Plate tectonics and Plate tectonics and igneous activity igneous activity
Plate motions provide the mechanism by which mantle rocks melt to form magma • Convergent plate boundaries
• Descending plate partially melts • Magma slowly rises upward • Rising magma can form
• Volcanic island arcs in an ocean (Aleutian Islands)
• Continental volcanic arcs (Andes Mountains)
![Page 43: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/43.jpg)
Plate tectonics and Plate tectonics and igneous activity igneous activity
Plate motions provide the mechanism by which mantle rocks melt to form magma • Divergent plate boundaries
• The greatest volume of volcanic rock is produced along the oceanic ridge system
• Lithosphere pulls apart • Less pressure on underlying rocks • Partial melting occurs• Large quantities of fluid basaltic magma are
produced
![Page 44: Earth Science, 12e Volcanoes and Other Igneous Activity Chapter 9](https://reader036.vdocuments.net/reader036/viewer/2022081506/56649d1e5503460f949f1ec3/html5/thumbnails/44.jpg)
Plate tectonics and Plate tectonics and igneous activity igneous activity
Plate motions provide the mechanism by which mantle rocks melt to form magma • Intraplate igneous activity
• Activity within a rigid plate • Plumes of hot mantle material rise• Form localized volcanic regions called hot spots • Examples include the Hawaiian Islands and the
Columbia River Plateau in the northwestern United States