• Worldwide distribution of active volcanos -- map
• Plate tectonic origin of igneous rocks -- igneous environments and relations to plate tectonics
• Plate tectonic origin of basalts
• Distribution of "hot spots" -- map showing present day hot spots over rising mantle plumes
• Low viscosity basalt flow -- river of molten lava
• Lava tube in pahoehoe -- allows efficient flow of molten basalt for long distances
• Pahoehoe burning house -- Hawaii
• Pahoehoe and aa basalt flows -- pahoehoe is more fluid because it's erupted at higher temperatures than the blocky aa
• Vesicular upper part of pahoehoe flow -- flow margins chill quickly and gas bubbles can be preserved
• Pillow basalts -- basalts erupted on the sea floor typically form pod-shaped "pillows"
• Close-up of a basalt pillow
• Origin of plateau basalts -- diagram
• Plateau basalt flows -- Columbia River basalts, exposed in Grand Coulee, WA
• Young plateau basalt flows -- Snake River plain, Idaho
• Fissure eruption -- plateau basalts are erupted from fissures (cracks) in the ground
• Lava fountain -- from fissure eruption of basalt in Hawaii
• Spatter cones -- small basaltic cones created by lava fountains along a fissure. Plateau basalts, Craters of The Moon Natl.Mon., Idaho.
• Feeder dike -- evidence that plateau basalts are erupted from fissures
• Baked contact -- lava flows may bake the materials beneath them a brick-red. The heat causes iron in the underlying materials to oxidize, yielding the color.
• Columnar basalt -- basalt flows may form hexagonal columns as the lava contracts and forms cracks (joints) on cooling
• Origin of shield volcano -- diagram. Typical basalt volcano.
• Shield volcano -- Belknap Cone, Oregon
• Shield volcano -- Newberry Crater, Oregon
• Fissure eruption -- basaltic eruption on on flank of Mauna Loa, Hawaii
• Volcano types -- diagrams of cinder cone, stratovolcano, shield volcano
• Cinder eruption -- Surtsey, Iceland. Basaltic cinder blasted out as lava meets sea water
• Cinder eruption -- nighttime view of eruption of Paracutin, Mexico
• Young cinder cone -- Lava Butte, near Bend, Oregon
• Older cinder cone -- Red Hill, near Bishop, California. Erosion has been at work on the cone and it no longer has sharp outline.
• Cinder cones of various ages -- near Flagstaff, AZ. The younger cinder cones are sharp and fresh, the older ones greatly eroded. Try to arrange the cones from youngest to oldest!
• Subduction zone and volcanic arc -- stratovolcanos are formed from andesite created by the melting of a downgoing oceanic plate
• Stratovolcano -- Mt. Shasta. Classic stratovolcano.
• Deposits on flank of stratovolcano -- shows alternating layers of volcanic ash and lava flows
• Stratovolcano -- Mt. St. Helens. South side, prior to 1980 eruption
• Blocky ash flow -- Mt. St. Helens, pre-1980
• Ash and lava flows -- Mt. St. Helens, pre-1980
• Volcanos in volcanic arc -- the Andes Mtns., Ecuador
• Lahar (volcanic mudflow) -- Formed by hot ash falling on ice and snow on volcano; resulting mudflow travels rapidly down river channels. Nevado del Ruiz, Ecuador
• Lahar deposits -- typical volcanic mudflow deposits
• Mt. St. Helens -- north flank, pre-1980-eruption
• Mt. St. Helens -- north flank, post eruption
• Mt. St. Helens -- diagram of collapse of north side of volcano
• Mt. St. Helens -- north flank collapsing in landslide
• Mt. St. Helens -- blast cloud moving northward
• Mt. St. Helens -- ash eruption after collapse of north side
• Caldera formation -- diagram showing formation of Crater Lake
• Crater lake caldera
• Tephra (ash) deposits at Crater Lake -- from collapse of Mt. Mazama
• Cross-section of rhyolitic plug dome -- diagram
• Rhyolitic plug domes -- the Mono Craters
• Mono Craters domes and obsidian flow
• Obsidian flow -- Steep rugged flow reflect high lava viscosity. North end of Mono Craters.
• Generation of pyroclastic ash flows -- diagram
• Pyroclastic ash flow cloud -- Mt. Pinatubo

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