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Mount St. Helens Before 1980 eruption After 1980 eruption
MEDIA 0600a1_Mount_St_Helens.kmz 0600a2_Pacific_NW.mov 0600a2_Pacific_NW_VE4.scene EXPLANATION Ash from eruption rose 25 km Ash spread across Washington, Idaho, and Montana Lava dome formed in crater after eruption Volcano constantly monitored by USGS 06.00.a During eruption 1
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Observe some characteristics of a volcano Commonly a hill or mountain
Can erupt lava or ash Vent where magma erupted Crater Can be erupted from fissure or depression, so not a hill INSTRUCTIONS TO STUDENTS Observe the photographs to recognize characteristics of a volcano EXPLANATION Not all volcanoes have classic cone shape, but many do 06.01.a 2
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Scoria cone also called cinder cone usually basaltic several hundred meters high Shield volcano gentle slopes usually basaltic with scoria and ash size ranges from a kilometer across to huge mountains NOTES Scoria cone: northern Arizona Shield volcano: Iceland
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Types of Volcanoes: Part 1
Scoria Cone Shield Volcano EXPLANATION Scoria cone also called cinder cone usually basaltic several hundred meters high Shield volcano gentle slopes usually basaltic with scoria and ash size ranges from a kilometer across to huge mountains NOTES Scoria cone: northern Arizona Shield volcano: Iceland 06.01.c 4
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Paracutin eruption of 1943
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Composite volcano Symmetrical mountains Interlayered lava flows, pyroclastic deposits, mudflows Mostly andesite, but also contains felsic and mafic rocks Volcanic dome dome-shaped constructed feature Solidified lava with volcanic ash and rock fragments Very viscous felsic or intermediate magma NOTES Composite volcano: Ecuador Dome: Mount St. Helens, Washington
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Observe these types of eruptions
Lava flow Lava fountain INSTRUCTIONS TO STUDENTS Observe these types of eruptions and discuss what you see with a classmate clow: magma erupts onto surface and flows away Lava fountain: gas propels molten pieces of lava into air Dome: viscous lava piles up around vent Eruption column: volcanic ash, pumice, rock fragments ejected into air Upper two photos are mafic and lower two are felsic (could bring in viscosity) EXERCISE If possible, do this introduction to eruptions by showing ten or so short video clips of different eruptions, with multiple examples of each type. Ask students to determine how many types of eruptions they witnessed and to write a list of the characteristics of each type. Do this before introducing any terms, and follow this exercise up by this slide where terms are introduced. NOTES Lava flow: Kilauea, Hawaii Lava fountain: Kilauea, Hawaii Dome: Mount St. Helens, Washington Eruption column: Augustine volcano, Alaska Dome Eruption column 06.02.a 7
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Observe these types of eruptions and discuss what you see with a classmate
clow: magma erupts onto surface and flows away Lava fountain: gas propels molten pieces of lava into air Dome: viscous lava piles up around vent Eruption column: volcanic ash, pumice, rock fragments ejected into air Upper two photos are mafic and lower two are felsic (could bring in viscosity) NOTES Lava flow: Kilauea, Hawaii Lava fountain: Kilauea, Hawaii Dome: Mount St. Helens, Washington Eruption column: Augustine volcano, Alaska
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How Do Gases Affect Magma?
Released gas propels eruption and forms ash What happens when you open a soda? Under less pressure, gas forms bubbles Opening top releases dissolved gas held in by pressure EXPLANATION Magma, like soda, contains dissolved gases including water, carbon dioxides, and sulfur dioxide As magma rises, pressure decreases and gases come out of solution Dissolved gas held in magma by pressure 06.02.b2 9
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Magma, like soda, contains dissolved gases including water, carbon dioxides, and sulfur dioxide
As magma rises, pressure decreases and gases come out of solution
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Felsic means high in silicon and aluminum
Felsic means high in silicon and aluminum. Felsic magma produces light colored igneous rocks. Volcanic eruptions of felsic magma are explosive! These eruptions produce much ash, rock and cinders. They also produce very hot clouds of ash called pyroclastic flows
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Mafic magmas contain less amounts of silica so less viscous
Mafic means low in silica; high in iron and magnesium Volcanic eruptions of this type are usually gentle with hot lava flowing out.
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Felsic magmas contain high amounts of silica so more viscous
Mafic magmas contain less amounts of silica so less viscous NOTES More viscous: Mount St. Helens, Washington Less viscous: Kilauea, Hawaii
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How Does Viscosity Affect Eruptions?
More viscous: difficult to flow and traps gas 06.02.c EXPLANATION Felsic magmas contain high amounts of silica so more viscous Mafic magmas contain less amounts of silica so less viscous NOTES More viscous: Mount St. Helens, Washington Less viscous: Kilauea, Hawaii Less viscous: flows easier and gas can escape 14
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Scoria Cones and Basalt Flows: Rock Types
Vesicular basalt Nonvesicular basalt EXPLANATION Vesicular basalt gas pockets calls vesicles occur in lava flows and ejected material such as scoria Nonvesicular basalt magma did not contain enough gas to form bubbles either did not start out with gas or degassed somewhere along the way Scoria vesicular basalt or andesite ejected from vent, such as a lava fountain blobs cool and solidify in the air to form cinders NOTES Photograph of eruption: Hawaii Scoria 06.03.a 15
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Features of Lava Flows Lava tubes AA lava Pahoehoe lava EXPLANATION
Lava tubes (Hawaii) surface of lava flow solidifies but interior still moving tube can drain, leaving behind cave AA lava (Hawaii) breaks apart into fragments as it flows Pahoehoe lava (Hawaii) surface forms small folds usually fed by a lava tube AA lava Pahoehoe lava 06.03.a 16
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Lava tubes (Hawaii) surface of lava flow solidifies but interior still moving tube can drain, leaving behind cave AA lava (Hawaii) breaks apart into fragments as it flows Pahoehoe lava (Hawaii) surface forms small folds usually fed by a lava tube
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