Chapter 18 Volcanic Activity
Lesson 5 Volcanoes: The Basics
Think About It… What happens when you shake a can of soda and then open it?
Focus Question… How does the composition of magma affect its explosiveness?
http://www.pbs.org/wgbh/nova/volcanocity/anat-08.html • What is magma? • A mixture of molten rock, suspended mineral grains, and dissolved gases deep beneath Earth’s surface Nyiragongo Volcano East African Rift Valley
http://www.ncgeology.com/Eno_interactive_webs/Geologic_Principles_igneous%20rocks.htmlhttp://www.ncgeology.com/Eno_interactive_webs/Geologic_Principles_igneous%20rocks.html 2. Types of Magma: Basaltic… • Gas Content • 1 – 2 % • Silica Content • 50% • Viscosity • low • Explosiveness • least • Origin/Location of Magma/Lava • oceanic/continental crust • Example • Mt. Kilauea in Hawaii Mt. Kilauea A Hot Spot Volcano
Types of Magma: Andesitic… • Gas Content • 3 - 4 % • Silica Content • 60% • Viscosity • intermediate • Explosiveness • intermediate • Origin/Location of Magma/Lava • continental margins • Examples… • Mt. St. Helens and Mt. Rainier (Washington) • http://vulcan.wr.usgs.gov/Volcanoes/MSH/Images/july_22_images.html
Types of Magma: Rhyolitic (Granitic) Yellowstone Volcano • Gas Content • 4 - 6 % • Silica Content • 70% • Viscosity • high • Explosiveness • greatest • Origin or Location of Magma/Lava • continental crust • Example • Yellowstone Supervolcano in Wyoming
http://www.hbci.com/~wenonah/history/img/krakatoa.jpg Types of Magma… 3. The higher the silica content… • the higher the viscosity (resistance to flowing)… • the greater the explosiveness! Krakatoa – Highly viscous and explosive!
http://romanmythology.wikia.com/wiki/Pluto Intrusive Activity… • What is a pluton? • An intrusive igneous rock body Pluto – god of the underworld http://earthsci.org/mineral/rockmin/chart/iroccur.gif
http://www.yosemiteriversideinn.com/ Batholiths 2. A batholith is the largest of plutons common in the interiors of major mountain chains. Yosemite – Part of the Sierra Nevada Batholith
Intrusive Activity… 3. Where did all the magma come from? • Scientists hypothesize that… • At subduction zones, a plate subducts, • melts, • cools into a pluton. http://herramientaslinker.com.ar/convergent-boundary-subduction&page=7
http://www.smate.wwu.edu/teched/geology/vo-eruption2.html Volcanoes… • What is lava? • molten rock that has reached Earth’s surface • What is a volcano? • A mountain or opening in Earth’s crust from which lava erupts Paricutin in Mexico, 1943
3. The Anatomy of a Volcano… • Vent – the opening in the crust through which lava erupts • Crater – bowl-shaped depression around the vent • Caldera – larger depressions around a vent where the volcano has collapsed into the magma chamber d. Magma chamber – area under the volcano which holds the magma
Slides of Crater, Caldera… • Crater Lake • Yellowstone Caldera
4. Label the Volcano… http://rbaadvisors.com/what-are-the-main-features-of-a-volcano&page=3
Types of Volcanoes… http://www.cnn.com/2014/10/28/us/hawaii-volcano/index.html IN THE NEWS… • Type of Volcano • Shield • How It Forms • Basaltic lava builds up (Quiet eruptions) • Description • Wide with gently-sloping sides • Example • Kilauea in Hawaii (hot spot) • Iceland (divergent) http://www.discoverhawaiitours.com/blog/tag/kilauea/
Types of Volcanoes… • Type of Volcano • Cinder cone • How It Forms • Ejected tephra falls back to earth and piles up (Explosive) • Description • Small but steep • Example • Paricutin in Mexico • Convergent boundary Paricutin, Mexico http://volcano.oregonstate.edu/vwdocs/volc_images/img_paricutin.html
Types of Volcanoes… • Type of Volcano • Composite • How It Forms • Tephra eruptions alternate with lava flows • Description • Large & steep • Example • Krakatoa • Mt. St. Helens • Convergent Mt. St. Helens -Before and After! http://pubs.usgs.gov/fs/2005/3045/images/fig1.jpg
A Composite Volcano… • http://www.pbs.org/wgbh/nova/volcanocity/anat-flash.html
Lesson 6 Volcanoes: Effects on the Lithosphere
Tephra… 1. What is tephra? • Rock fragments thrown into the air during a volcanic eruption Tephra classified by size… • dust ash lapilli bombs blocks 2. A pyroclastic flow is… • an eruption of gas, ash, and other tephra • These types of eruptions can be extremely violent and deadly because… the PC flow moves very fast and is very hot. 3. Ash and dust from a pyroclastic flow blocks sunlight and lowers global temperatures.
Effects of a Volcanic Eruption… Lahars • A lahar is a mixture of mud & debris created when… • heat from an eruption melts snow OR • rain forms around dust or ash in the atmosphere. http://volcanoes.usgs.gov/hazards/lahar/index.php
Earthquakes, Landslides and Tsunamis… • Earthquakes are caused when… Magma breaks rocks as it makes its way to the surface. • Landslides are caused in two ways… … a volcanic earthquake (EQ) or the eruption itself causes land to slide • Tsunamis are caused when… … the volcanic landslide “bulldozes” water ahead of it
Earthquakes, Landslides and Tsunamis… http://volcanoes.usgs.gov/hazards/landslide/index.php http://volcanoes.usgs.gov/Imgs/Jpg/Unzen/MayuyamaSlide_large.jpg
5. Hawaii and Yellowstone… • … are formed at hot spots (very hot places in the mantle/crust) • … away from plate boundaries
6. Kilauea: Effects on Land… Basaltic lava… • burns vegetation and buildings • creates new land (16 acres a year!) http://www.ncgeology.com/Eno_interactive_webs/Geologic_Principles_igneous%20rocks.html
7. Krakatoa: Effects on Land… The eruption of Krakatoa… • Created a caldera when it blew the island apart • Caused a pyroclastic flow and tsunami (1883) http://www.ncgeology.com/Eno_interactive_webs/Geologic_Principles_igneous%20rocks.html
8. Iceland: Effects on Land… Iceland’s volcanoes in the rift valley are causing it to grow bigger – with older rocks on the east and west sides of the island.
Convergent Boundary Volcanoes • Ocean plates subduct under other plates and melt to form magma • Location – the Pacific Ring of Fire, the Mediterranean Belt Mt. Vesuvius and Pompeii Victims http://mrbpielglobal.edublogs.org/files/2010/12/vesuvius_24417-1qnp5rt.jpg
The Ring of Fire… http://pubs.usgs.gov/gip/dynamic/graphics/Fig22.gif
Divergent Boundary Volcanoes • As plates move apart, magma is forced upward into fractures and faults • Location – East Africa Rift Valley, mid-ocean ridges, Iceland
http://rajeshsivananth.files.wordpress.com/2010/07/surtsey.jpghttp://rajeshsivananth.files.wordpress.com/2010/07/surtsey.jpg Divergent Boundary Volcanoes… Iceland Surtsey Volcano
A Plethora of Plutons… Stocks • Stocks are irregularly-shaped plutons similar to batholiths but smaller. http://belmont.sd62.bc.ca/teacher/geology12/photos/volcanoes/plutons.jpg
A Plethora of Plutons… Laccoliths http://facweb.bhc.edu/academics/science/harwoodr/geol101/study/Plutons.htm • Laccoliths are mushroom-shaped plutons with a round top and a flat bottom.
http://facstaff.gpc.edu/~pgore/geology/geo101/plutons.php A Plethora of Plutons… Sills • A sill is a pluton that forms when magma intrudes parallel to layers of rock. The Palisades Sill, NY
A Plethora of Plutons… Dikes http://www.exstrom.com/hbaromega/irondike.html • A dike is a pluton that cuts across preexisting rocks. Iron Dike Intrusion, Ironclads, Colorado