Transcript Volcanoes
Section 6.1 • Vocabulary to know: • • • • • • • • • • • • • • • • • • • Volcano Quiet eruptions Explosive eruptions Crater Central vent Dike Lava Pipe Magma chamber Magma Aa Pahoehoe Pillow lava Blocky lava Pyroclastic Volcanic bombs Lapilli Volcanic ash Volcanic blocks What is a Volcano? • Volcano–a mountain that forms when magma (As well as volcanic gases) reaches the surface How do volcanoes form? Magma reaches Explosive the surface eruption. Boiling through a vent mud and ash are hurled into the air Hot lava then flows out through the vent. The lava cools and hardens The process keeps on repeating itself making the volcano grow larger Types of Eruptions • Quiet (Non explosive) eruptions– Have very hot, low silica, low viscosity magma • Explosive eruptions– High amounts of water – High silica, and high viscosity magma • Clogs a volcanic pipe… • Enormous pressure builds up… • Steam gets trapped… • Volcano explodes!!! Non explosive volcanic eruptions • 4 different types of lava: Aa- forms brittle crust…crust gets torn into little pieces as lava flows underneath Pahoehoe- flows very slowly…like wax dripping from a candle Pillow lava- forms when eruptions occur underwater Blocky lava- cool and stiff. Doesn’t travel far from the erupting vent of the volcano Volcano Structure 1. Crater• bowl shaped pit at top of central vent 2. Central vent• magma escapes to the surface 3. Dike• leads to side vent 4. Lava• magma that has reached the surface 5. Pipe• narrow vertical channel 6. Magma chamber• pocket where magma collects Explosive volcanic eruptions • Produce pyroclastic material– Forms when magma explodes from a volcano and solidifies in the air – 4 types: Volcanic blocksVolcanic bombs•Large blobs of magma that harden in the air Lapilli•Pebble-like bits of magma that harden before they hit the ground Volcanic ash•Majority of pyroclastic material •Solid pieces of rock erupted from volcano What are pyroclastic flows? • Pyroclastic flow– Very dangerous – produced when enormous amounts of hot ash, dust, and gases are ejected from volcano – can race downhill at speeds of more than 200 km/h – temperature at the center can exceed 700°C Section 6.2 • Vocabulary to know: • Shield volcano • Cinder cone volcano • Composite volcano Shapes of Volcanoes • Shield volcano: – Broad – Gently sloping • Eruptions: – Hot, flowing basaltic lava. – Travels a long way before it solidifies Mount Kilauea (Shield Volcano) • Located in Hawaii • Presently the most active volcano on the planet • Can be walked up to because of its non-violent explosions Shapes of Volcanoes • Cinder cone volcano: – Small – Steep sides • Form from: – Ash and cinders that are ejected into the air and fall back onto the volcano Shapes of Volcanoes • Composite volcano: – Tall – Steep sides • Built up from viscous lava, ash, and volcanic bombs • Eruptions: – High silica – High viscosity Mount St. Helens • Composite volcano • Erupted on May 18, 1980 • Killed over 55 people • Blast removed 1000 ft off the top of the volcano • The explosion could be heard as far away as Canada • Notice the trees… Krakatau • Composite volcano • Erupted on August 26, 1883 in Indonesia • Explosions were heard 2200 miles away in Australia • Ash was propelled 50 miles into the air – This ash blocked the sunlight for 2 ½ days • Created a tsunami 120 feet tall • Killed 36,000 people Mount Vesuvius • Composite volcano • Erupted in Pompeii in 79 AD • 10 feet of ash piled on top of the buildings after the explosion • Considered to be one of the most dangerous volcanoes in the world – 3,000,000 people live close to it Mount Pinatubo • Erupted in 1991 • A 7.7 Richter scale earthquake caused the volcanic eruption • Scientists predicted the eruption, and the residents were evacuated • Caused the entire world’s temperatures to drop by 1 degree Section 6.3 • Vocabulary to know • • • • • Plate boundary Ring of fire Divergent boundary Convergent boundary Hot spot Most Volcanoes Occur at Plate Boundaries Ring of Fire • Mostly found along the edge of the Pacific plate • Contains nearly 75% of the worlds active volcanoes found on land Divergent Boundary • Magma escapes to the surface as the plates move apart – Magma rises to fill the gap between the two separating plates – Mid ocean Ridge Convergent Boundary • Oceanic plate is subducted into the mantle… • This causes melting… • Magma forms and rises to the surface… • Volcano created!!! • Why does the magma rise? – It’s less dense than the rocks around it. Hot Spot • Hot spot stays in one place… • Plates move over the top of it… • Over time, a chain of volcanoes is formed!!! • Is Kauai an active volcano? Iceland • Above sea level because there is a hot spot that works with the mid ocean ridge • What rocks would be the oldest? • What would happen to a house built on the mid ocean ridge?