2 Volcanoes and Plate Tectonics Volcano - a weak spot in the crust where molten material, or magma, comes to the surface.Magma – molten mixture of rock forming substances, water and gases beneath the mantleLava - Magma that reaches the surface
3 Volcano FormationAlong Tectonic Plate BoundariesAbove a hot spot when magma erupts through the crust and reaches the surface.
4 Ring of Fire - Major Volcanic Belt surrounding the Pacific Ocean Tectonic Plate Boundaries
5 Volcanoes along spreading boundaries or colliding boundaries Island arcs – where 2 oceanic plates collide -
6 Hot Spot Volcanoes – https://www. youtube. com/watch
7 Volcanic EruptionsVolcano AnatomyMagma Chamber -magma collected inside a volcano pocketPipe - a long tube that connects the magma chamber to Earth's surface.Vent - an opening through which the magma leaves the volcanoCrater - a bowl-shaped area around a volcano's central vent.Lava Flow – an area covered by lava as it flows out of the vent
8 As magma rises toward the surface, the dissolved gas begins to expand as pressure decreases and this exerts an enormous upward force on the magma.When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent.
9 Kinds of Volcanic Eruptions QuietExplosiveType depends onMagma’s silica contentThin and runny/ thick and sticky magmaGas contentSilica – material found in magma that is formed from oxygen and silicon
10 Quiet Eruptions Low silica magma Magma is thin, runny, flows easily Gases bubble gentlyOozes quietly from the vent and flowsHawaiian Islands formed from quiet eruptions
11 Quiet eruptions produce two different types of lava – Pahoehoe –Hot, fast moving, thin and runnyLooks like rope like coilsAa –Cooler, slow moving, thickerthan pahoehoe.Forms jagged lava chunks
12 Explosive EruptionsHigh silica magmaThick and sticky
13 Lava has different size particles - Volcanic ash – fine, rocky,(speck of dust or flour)b. Cinders – pebble sizedc. Bombs – size of a baseball toa car
14 Pyroclastic FlowPyroclastic Flow -an explosive fast-moving current of hot gas and rock (1800 0F/6500c) hurls out ash, cinders, and bombs.
15 Rocks formed during explosive eruptions – Obsidian – lava cools quickly, smooth surfacePumice – fast cooling lava with bubbles trapped in, leaving spaces
16 Mt. St. Helen’s EruptionMay 18, 1980 eruption triggered 5.1 earthquake57 People killed7,000 big game animals, 12 million Chinook and Coho salmon, and millions of birds and small mammals are believed to have died$1.1 billion in property damages for timber loss, etc.
17 Mt Vesuvius & Pompeii, Italy Erupted in 79 AD, approximately 20,000 people were killed in this eruptionPompeii is buried & is covered in a pyroclastic flow of cinders, ash, and mud around 20 feet high.
18 Active, Dormant or Extinct? active volcano - is one that is erupting or has shown signs that it may erupt in the near future.Mt. Shasta (1700s) and Lassen Peak (1915, 1921) in CAdormant volcano is not active now but may become active in the future.extinct volcano is unlikely to erupt again
19 Landforms from Lava and Ash Shield VolcanoesCinder ConeComposite VolcanoesLava Plateaus
20 Shield Volcanoes Composed mainly of runny lava flows Wide, gently sloping mountainsLargest volcanoes in the worldAn example: Hawaiian IslandsGentle slopes & domed shaped
21 Cinder Cone Volcanoes Made mostly of cinders and other rock particle Little or no lava flowsFormed from explosive type volcanoes (high silica)Narrow base and steep sidesExample: Black Butte in Northern Calif.
22 Composite VolcanoesTall, cone shaped mountains. Built up of alternating layers of ash and lavaExamples: Mt. Vesuvius in Italy, Mt St. Helens, Mt Shasta, Mt Lassen
23 Lava Plateaus Soils from Lava and Ash Layers of thin, runny lava flow and solidify on top of earlier layers. Columbia Plateau in Washington, Idaho, and OregonSoils from Lava and AshVolcanic ash releases potassium and phosphorous that plants need. Volcanic soil is fertile.
24 Volcanic Landforms: Calderas Huge hole left by the collapse of a volcanic mountainAn enormous eruption may empty a volcano's main vent and magma chamber. With nothing to support it, the top of the mountain collapses inward.Yellowstone in Wyoming, Crater Lake in OregonYellowstone Caldera is huge!!34 miles x 45 MilesWhole caldera is slowly rising causing lake to tilt & run toward southeast
25 Landforms from MagmaVolcanic Neck - magma hardens in a volcano's pipe. The softer rock around the pipe wears away, exposing the hard rock of the volcanic neck.
26 A sill forms when magma squeezes between horizontal layers of rock and hardens.
27 Dike – a vertical column of cooled magma that forms when magma intrudes (forces itself) across rock layers and hardens.
28 Sills and dikes are intrusions – an intrusion is always younger than the rock around it.
29 Batholith -a large body of magma cools inside the crust, a mass of rock