Transcript Volcanic
Volcanic Landforms Processes and Hazards Volcanic Landforms 1. 2. 3. 4. Intrusive Igneous Forms Extrusive – Basalt Landforms Extrusive – Composite volcanoes Extrusive – Rhyolite landforms 1. Intrusive Igneous Forms Magma solidified at great depth (so mineral sizes are large) Plutons (individual magma chambers) Batholiths (merged magma chambers) Pluton seen because of glacial erosion, Chile Brandberg, Western Namibia Intrusive igneous rocks are often more resistant to erosion, so they are topographic highs Plutons (individual magma chambers) Large Batholiths (merged magma chambers) Laccolith (bubble up strata) Small Dikes – vertical magma cutting through Sill – horizontal magma inserted between Dike, Spanish Peaks, Colorado more resistant than surrounding sediment, so stand out Dike, Picture Gorge Volcanic Neck. Dike Over time, the less resistant rock (i.e., pyroclasts and less consolidated lava flows) comprising the flank of the volcano is eroded away leaving the resistant neck exposed in relief. Shiprock (Tse bi Dahi, Rock With Wings), New Mexico is the classic example of a volcanic neck (base of composite volcano, so deep that is intrusive rock) Classroom Resource Tse bi Dahi “Rock With Wings” Shiprock Volcanic Neck 2. Extrusive – Basalt Landforms • • • • Basalt Flow Flood Basalts Cinder Cone Shield Volcano Shield & Cinder Cone – from basalt eruptions Later: Composite volcano Basalt flows will travel great distances and slope angles will reflect low viscosity. Classroom Resources Recent Hawaii Eruptions (NPS) A year of pahoehoe Spatter Cone Classroom Resources Etna Tourist Office No Lives Lost Different Textures, Same Basalt Rock Pahoehoe a’a Lava Tubes – so fluid that inside keeps moving & creates caves Classroom Resource Lava tube breakout Lava Tube, Hawaii near Flagstaff, AZ Mt St. Helens, OR Buries old topography Flood Basalt, Southern Utah Flood Basalt Flood Basalt, Oregon Cinder Cones SP Crater, AZ Cinder drops out (like hour glass) Cinder Cone Developing Largest drop out first Classroom Resource Cinder Cone Bombs Largest Clasts: Volcanic Bombs Crater: depression at top formed by force of eruption Owens Valley, Calif Very common in Arizona: especially S.F. Volcanic Field Sunset Crater, AZ Shield Volcanoes Isabela Island, Galapagos Hawaii built from Shield Volcanoes Weight of new lava has depressed the crust around Hawai’i Moat ~ 5000 m Below Sea Level Mauna Loa: note gentle profile from fluid basalt flows Mauna Kea Often have Summit Caldera – from collapse as lava flows away 3. Extrusive – Composite Volcanoes Mt Ararat, Armenia Composite Volcano, Oregon Sit above Subduction Zones Fuji Egmont Extraordinarily Dangerous from Nova from Nova from Nova Future Disaster: Popocatepetl, next to Mexico City & Puebla Composite Volcano Online Animations Volcanic Hazards http://serc.carleton.edu/NAGTWorkshops/vis ualization/collections/volcano.html Classroom Resources Nuee Ardente (also called glowing avalanche, pyroclastic flow) Set to music (www.mvo.ms) Soufriere, Montserrat Nuee Ardente (Glowing Avalanche or pyroclastic flow) Mt. Vesuvius Pompeii, Italy Volcanic Ash Debris Avalanche Mt St. Helens Before Eruption Classroom Resource Lahaar, Mt St. Helens Fly Over Mt Mazama (could be Rainier) Caldera – from collapse after lava has “evacuated” from magma chamber Crater Lake Mt Hood (my bet to go next) Mount Pinatubo Classroom Resources Colorado has no active volcanoes! 4. Extrusive – Rhyolite Landforms Small Eruptions: Rhyolite Domes, Mt Elden Rhyolite so viscous has trouble flowing, so piles up in dome shape Many Rhyolite Domes near Mono Lake, Calif Mammoth Lakes, still active evidence: carbon dioxide Classroom Resources After major eruption of composite volcano, will often start to rebuild with rhyolite domes Arizona has many rhyolite caldera super eruptions (17-27 myr ago) Superstition Mtns Chiricahua Mtns Toba – almost did us in