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VOLCANOES

VOLCANOES. Types of Volcanoes & Volcanic Landforms. TYPES OF VOLCANOES. There are three basic types of volcanoes: Shield Volcano Cinder Cone Composite Cone (Stratovolcano). This diagram shows the relative sizes of the three types of volcanoes. Types of Volcanoes. Shield Volcano

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VOLCANOES

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  1. VOLCANOES Types of Volcanoes & Volcanic Landforms

  2. TYPES OF VOLCANOES • There are three basic types of volcanoes: • Shield Volcano • Cinder Cone • Composite Cone (Stratovolcano) This diagram shows the relative sizes of the three types of volcanoes

  3. Types of Volcanoes • Shield Volcano • Large broad domes • Mostly basaltic lava • Shallow slopes • Very little pyroclastics • Examples are Mona Loa & Kilauea on Hawaii • Mona Loa is over 4000m above sea level & 9000m total from sea floor to summit Top: With a Pahoehoe lava flow in the foreground, Mona Loa is shown towering in the background Bottom: Active Kilauea crater is the summit of shield volcano

  4. Types of Volcanoes • Cinder Cone • Small individual peaks reaching maximum height of 300 m • Made up of ejected pyroclastics • Steep, high angle slopes • Very little lava erupted • Examples are Sunset Crater (AZ), Mt. Capulin (NM), & Mt. Paracutin (Mexico) • Cinder cones usually have a very short life span & form in clusters Top: Sunset Crater, AZ Right: The summit of Mt. Capulin can be reached by car Left: Diagram showing a typical cinder cone

  5. Types of Volcanoes • Composite Volcano (Stratovolcano) • Large symmetrical mountainous cones • Made of alternating lava and pyroclastics High angle slopes ~ 35°, can reach heights of 3000 m • Some examples are Mt. Fuji, Mt. St. Helens, Mt. Pinatubo, Mt. Shasta, Mt. Rainer, Mt. Vesuvius, & Mt. Etna • These are the dangerous, explosive, “Ring of Fire” volcanoes Top: Pinatubo explodes in 1991 Right: Mt. Shasta is the most southern volcano in the Cascade range Left: Mt. Rainer of the Cascades looms over nearby Seattle

  6. Examples of U.S. Composite Cones • The entire Cascade Range in the Pacific Northwest is made up of a dozen active strato-volcanoes • These volcanoes are explosive because of the type of magma that erupts out of them • The subducting oceanic Juan de Fuca plate has a high amount of water dissolved in it • It melts and rises up through the continental crust and becomes more granitic (thicker, higher gas content, more viscous, etc…) • That change gives the magma the potential to be very explosive

  7. Compare the three again • Cinder cones are the smallest and are made of pyroclastic eruptions • Shield volcanoes are the largest and are made of lava flows • Composite volcanoes are the most dangerous and are made up of both lava flows and pyroclastic eruptions

  8. Types of Volcanoes • All volcanoes can be characterized into one of three groups: • Active – the volcano has erupted in recent times and is expected to erupt again • Dormant – the volcano has erupted in historical times and there is evidence that it may erupt again • Extinct – the volcano has not erupted in historical times and there is no evidence that it will ever erupt again All volcanoes have a life cycle, and some will live much longer than others depending upon the energy contained within the magma Once the magma source beneath the cone has been completely depleted, the volcano will be come extinct

  9. Extra-Terrestrial Volcanism Left: Olympus Mons is the massive shield volcano on Mars which reaches a height of 27km; compare Mt. Everest at a height of 8.8km Right: IO is Jupiter’s innermost moon which has dozens of active volcanoes ejecting hot gases into its atmosphere • Earth is not the only planet in our solar system with volcanoes • Both Mars and Venus have large extinct volcanoes • The Jovian moon IO, is the only other planetary body to have active volcanism

  10. Volcanic Destruction • Nuee Ardente • This is the other name for a pyroclastic flow • A cloud of superheated gas, ash, and dust reaching speeds of 200 km/hr • Races down mountain with temps. exceeding 300°C • Large nuee ardentes may travel up to 100 km or more and will incinerate everything in its path Top: A nuee ardente roars down the slope of this Columbian volcano Bottom: Click on the picture to see a nuee ardente on an island arc volcano

  11. More Death & Destruction • Lahar • A large mudflow that washes away and buries anything in its wake • Triggered by an eruption that melts the ice and snow found the summit of a volcano • Very dangerous and quite unstoppable Top: The awesome force of lahars is evident by the burying of this car Bottom: Click window to see video of a mini-lahar; note the muddy consistency of the water

  12. VOLCANIC LANDFORMS • Caldera - a large crater (1 km or more across) formed when a volcano erupts, & collapses in on itself • Examples are: • Crater Lake, OR. • Pinatubo Caldera • Kilauea Caldera Top: Diagram depicts the formation of Crater Lake Right: Arial photo shows the 6 km wide Caldera of Crater Lake, OR Left: The remnant of Mt. Pinatubo

  13. More Volcanic Landforms • Volcanic Plug (neck) • When an extinct volcano erodes and leaves behind the solidified magma chamber • It is the ancient crystallized core of a volcano Shiprock in NW New Mexico is a very famous example of a volcanic plug Notice the long ridge that extends from the ancient heart; this is an igneous dike

  14. More Volcanic Landforms • Fissure Eruptions • When very low viscosity lava pours from long narrow cracks in the crust it will form extensive rivers and seas of lava • These are made from basaltic, non-explosive lavas, and can flow for 10s – 100s of km • Examples of what we call flood basalts can be found in the Pacific NW

  15. More Volcanic Landforms • Pyroclastic Flow Deposits – when a nuee ardente completes its fiery destruction, the fragments leave a very distinct deposit Top: a pyroclastic flow deposit of large block and bomb sized particles Bottom: Note the bedding planes from the fine ash

  16. Volcanoes can come in three varieties: shield volcano, cinder cone, & composite volcano Examples of Cinder cones: Sunset Crater, Mt. Capulin, and Mt. Paracutin Examples of Shield volcanoes: Mona Loa, Kilauea, and Olympus Mons (Mars) Examples of Composite volcanoes: Mt. St. Helens, Mt. Rainer, Mt. Shasta, Mt. Vesuvius, Mt. Fuji, Mt. Pinatubo, and Krakatau Volcanoes can be classified as either active, dormant, or extinct Most death and destruction from volcanic eruptions does not come lava, but from pyroclastic flows and lahars Volcanic landforms take on four basic types: Caldera craters Volcanic plugs Flood basalt deposits Pyroclastic flow deposits To Review:

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