PowerPoint PresentationQuestions to ponderThe relationship of Volcanism to Plate TectonicsMost of earth’s volcanism occurs at mid ocean ridgesSlide 5Hot SpotsHawaiian Hot spotSlide 8Yellowstone Hot spotHot spots around the globeSlide 11Slide 12Slide 13Slide 14Central vent volcanoes1. Shield volcanoesShield volcanoesSlide 182. Cinder conesSlide 20Slide 213. Composite cones (also called stratovolcanoes)Slide 23Slide 24Slide 25Which is potentially larger: a shield or composite cone?4. Volcanic DomesSlide 28Slide 29Lava dome forms in the crater of Mount St. Helens5. CalderasCrater Lake, ORMorphology of various volcanoes Shape provides clues towards the type of volcanoVolcanic hazardsLavaGasesAshTambora, Indonesia 1815Pyroclastic flows (Nuee Ardentes)Pyroclastic flow Mayon Volcano, Philippines 1984.Slide 41Mt. Pelee, Martinique1902 (Caribbean)Lahars (mudflows)LaharsSlide 45Slide 46Slide 47Slide 48Explosivity of volcanoesSlide 50Mount St. Helens, 1980Slide 52Slide 53Slide 54Slide 55Slide 56TsunamisKrakatau 1883 (Krakatoa)Slide 59“Supervolcanoes”Slide 61Slide 62Slide 63Slide 64Slide 65Lecture 10Types of Volcanoes & Volcanic EruptionsQuestions to ponder•What is the relationship between volcanoes and plate tecontics•How does magma composition control the type of volcano, its explosivity and other hazards?•How are central vent volcanoes classified? How does the volcanic material influence cone shape/tyle?•Why are “supervolcanoes” such a major concern? Where are some of these located?The relationship of Volcanism to Plate Tectonics•Volcanoes associated with–Divergent Zones•Mid ocean ridges•Some continental rifts–Convergent Zones•Oceanic to oceanic subduction•Oceanic to continental subduction–Hot spots or Mantle plumesMost of earth’s volcanism occurs at mid ocean ridgesDivergent ZonesHot Spots•Not related to Plate Boundaries•Stationary mantle plumes melt crust of plate that slowly drifts over the plumeHawaiian Hot spotHawaiian Hot spotThis is yet another way we know that lithospheric plates moveWe can also calculate the relative rates of plate movement byDividing the age of rocks by their distance from the Hot SpotYellowstone Hot spotHot spots around the globeVolcanoes can be divided into two broad categories:•Fissure eruptions–Lava and/or pyroclastic material flow outward from a large cracks or “fissures”–Flood basalts and basalt plateaus are the result•Pyroclastic floods can occur, too•Volcanic “cones”–Lava and pyroclastic material emanates from a central vent–Generally build conical peaks–Several varieties of volcanic cones, the type dependent upon the material producedFissure eruptionsFissuresFissuresFlood basaltsActive fissuresPyroclastic flows(ash sheet deposits)Central vent volcanoes•Many different landforms as a result of the magma composition, explosivity, etc.•The morphology (shape) of a volcano can tell you much about the hazards and materials•Types of central vent volcanoes:–Shield Cones–Cinder Cones–Composite Cones–Domes–Calderas and “Supervolcanoes”1. Shield volcanoes•Gentle, broad, flat volcanoes•Can be the largest volcanoes•Built from lava flows•Result of lava viscosity•Basalt (low viscosity)•Little magma mixing or differentiation•Example:–HawaiiShield volcanoes2. Cinder cones•Small, steep-sided cones–Smaller parasitic cinder cones sometimes develop in close proximity to other volcanic forms•Viscous lava approaches surface•Lower pressures cause sudden release of gases•Pyroclastic material is rapidly ejected which falls around vent to build the cone•Example: Paricutin, MXCinder cone in HawaiiParicutin, MX3. Composite cones(also called stratovolcanoes)•Large steep-sided cones•Alternating layers of lava and pyroclastic material•Common volcanic form along subduction zones•Produces “stratified” layers•Often a result of viscous lava–Intermediate composition–Can be explosive–Produce pyroclastic flowsMt Baker, WAMt Baker, WAMt. Jefferson, ORMt. Jefferson, ORMt Rainier, WAMt Rainier, WAWhich is potentially larger: a shield or composite cone?4. Volcanic Domes•Extremely viscous lava (Felsic to Intermediate) builds smaller, bulbous forms•Often a component of other volcanoes–Especially common in composite volcanoes•Can be very explosiveLava dome forms in the crater of Mount St. Helens5. Calderas•Large depressions left after explosive eruptions•Calderas can be found around the globeWater will frequently infill the resulting crater to form a lakeCrater Lake, ORMorphology of various volcanoesShape provides clues towards the type of volcanoThe morphology is a result of the type of materials which built the structureVolcanic hazards•Lava – discussed last time–Usually not a direct hazard to life but can destroy property•Gases - discussed last time–Toxic clouds have caused deaths–Environmental effects•Ash- discussed last time–Threats to aircraft, vehicles, agriculture, buildings, climate•Pyroclastic flows–Immediate hazard to those downslope•Lahars (Mudflows)–Immediate and long term hazard to people downslope•Explosivity–Can be directly hazardous; a function of magnitude•Tsunamis–Can affect people far from source•Long term effects….–Climate; creation of landmass; changes in topography and streamsLavaGasesGases produce acid rain,and also toxic clouds of CO2As well as other compoundsAsh•Effect depends upon the volume of material ejected but can be potentially produce a large impact on a global scaleAsh and aerosols in upper atmosphere from Mount PinatuboAsh and aerosols in upper atmosphere from Mount PinatuboProduced vibrant sunsets and resulted in minor global T decreaseProduced vibrant sunsets and resulted in minor global T decreaseTambora, Indonesia 1815•100 km3 of ejected tephra blanketed communities in a several hundred km radius•Over 80,000 died as a result of post-eruption starvation•Ash cloud dropped global temperatures by about 3˚C and resulted in “the year without summer” for Europe and North America in 1816`Pyroclastic flows(Nuee Ardentes)•Hot glowing cloud (1000 + degrees C) of pyroclastic material that can move at velocities of 100 mph!•Generally follows topography•Very hazardous to those living downslope!•Destroys everything in it’s path•Can even travel across water!Pyroclastic flowMayon Volcano, Philippines 1984.Eminent danger you CANNOT outrun!Mt. Pinatubo, Phillipines,