Transcript Volcanoes
Volcanoes Ch 8 1 Bill Nye Volcano Video 2 What is a Volcano? A volcano is a weak spot in the crust where molten material, or magma, comes to the surface Magma lava reaching the surface is called 3 Location of Volcanoes 600 active volcanoes worldwide Many more are found beneath oceans Most occur in belts that extend across continents and oceans 4 Burning Ring of Fire A major belt is the “Ring of Fire” which encircles the Pacific Ocean 5 Most volcanoes occur along diverging plate boundaries such as the mid-ocean ridge, or in subduction zones, around edges of oceans 6 7 “Hot Spot” volcanoes form where magma from deep within the mantle melts through the crust like a blow torch – Examples: – Hawaiian Islands – Yellowstone National Park 8 Hawaiian Hot spots Video 9 10 Inside a Volcano All volcanoes have a pocket of magma beneath the surface and one or more cracks through which magma forces its way through Magma pocket is called a magma chamber 11 A pipe is a long tube in the ground that connects the magma chamber to the earth’s surface Molten rock and gas leave the volcano through an opening called a vent 12 A lava flow is the area covered by lava as it pours out of a vent A crater is a bowl-shaped area that may form at the top of a volcano around the central vent 13 14 Types of Volcanic Eruptions The silica content of magma helps to determine whether the volcanic eruption is quiet or explosive Silica is the material formed from the elements silicon and oxygen 15 Silica is one of the most abundant materials in Earth’s crust and mantle The more silica that magma contains, the thicker it is 16 Quiet Eruptions: Magma flows easily; the gas dissolved in the magma bubbles out gently Creates island arcs which are a chain of volcanic islands – Examples: – Hawaii – Iceland 17 Produce two types of lava: Pahoehoe - fast moving, hot lava; Surface looks like a solid mass of wrinkles, billows, and rope-like coils 18 Aa - cooler, slower-moving lava; when hardens, forms a rough surface consisting of jagged lava chunks. Mafic- rich in magnesium and iron; this is the kind of lava flows out of oceanic volcanoes. 19 Explosive Eruptions: Magma is thick and sticky Magma slowly builds up in the volcanoes’ pipe Dissolved gases cannot escape Trapped gasses build up pressure until they explode 20 A pyroclastic flow occurs when an explosive eruption hurls out ash, cinder, bombs, and gasses Another name for this kind of lava is called tephra. 21 Stages of a Volcano Active - is erupting, or has shown signs that it may erupt in the near future Dormant - does not show signs of erupting in the neat future Extinct - unlikely to erupt 22 Types of Volcanoes – Shield Volcano: – Thin layers of lava pour out of a vent and harden on top of previous layers – Example: Hawaiian Islands 23 24 Cinder Cone Volcano: – Form when cinders from a vent, pile up around the vent, forming a steep- coneshaped mountain 25 Composite Volcano Layers of lava alternate with layers of ash, cinders, and bombs 26 Types of volcano music video 27 1. FYI-Super Volcano video 2. Super volcano simulated eruption video 28 Related Volcanic Activities Hot Spring - groundwater heated by a nearby body of magma rises to the surface and collects in a natural pool 29 Geyser - forms when rising hot water and steam become trapped underground in a narrow crack Pressure builds until the mixture suddenly sprays upward, clearing the crack 30 31 Related Volcanic Landforms – Caldera: – A large hole at the top of a volcano formed when the roof of a volcano’s magma chamber collapses 32 Formation of a Caldera 33 – Dike: – A slab of volcanic rock formed when magma forces itself across rock layers – vertical rock formation 34 Sill: A slab of volcanic rock formed when magma squeezes between layers of rock (horizontal rock formation) 35 sill 36 Batholith: A mass of rock formed when a large body of magma cooled inside the crust 37 – Dome Mountains: Rising magma within the crust is blocked by layers of rock Magma forces layers of rock to bend upward into a dome shape Example: Black Hills 38 Dome Mountains 39 Watching Activity Seismometer – is an instrument that detects Earth’s movements. These movements tell if the volcano is about to blow its top. Tiltmeter- measures any change in the slope of an are. This can tell if the land is bulging and ready to blow. 40 Volcanologists Scientists that study volcanoes 41 Mount Vesuvius Erupted in AD79 near the city of Pompeii, Italy 42 Trapped in Time The volcano eruption was deadly Lava, ash, hot gases poured out of the volcano The ashes covered everything For hundreds of years the city remained buried under the ash 43 44 45 Volcanic Rock Obsidian Pumice 46 Pompeii –Last Day http://www.smm.org/pompeii/video/ ?size=medium 47 Vocabulary: Erupts Volcano Magma Lava vent Cinder cone Shield cone Composite cone Volcanologists Island arc Seismometer Tiltmeter Hot spot Calderas Magma chamber Pipe Lava flow crater 48 Questions : What are volcanoes? How are they formed? What are the types of volcanoes? How do volcanoes change the Earth’s surface? Stages of a volcano? What is the ring of fire? What are the differences between quiet eruptions and explosive eruptions? What are the volcanic related landforms? 49