Volcanoes Environmental Geology, Mr. Paul Lowrey Stacey Singleton, Cassandra Combs, Dwight Stephenson, Matt Smithyman EMPACTS Project, Spring 2017 Northwest Arkansas Community College, Bentonville, AR 72712
Volcanoes A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
How and where are volcanoes formed? Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle. Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging.
Types of Volcanoes Cinder Cone Composite Shield Lava Domes
Cinder Cone These are the simplest type of volcano. They occur when particles and blobs of lava are ejected from a volcanic vent. The lava is blown violently into the air, and the pieces rain down around the vent. Over time, this builds up a circular or oval-shaped cone, with a bowl-shaped crater at the top. Cinder cone volcanoes rarely grow larger than about 1,000 feet above their surroundings.
Composite Composite volcanoes, or stratovolcanoes make up some of the world s most memorable mountains: Mount Rainier, Mount Fuji, and Mount Cotopaxi. These volcanoes have a conduit system inside them that channels magma from deep within the Earth to the surface. They can have clusters of vents, with lava breaking through walls, or issuing from fissures on the sides of the mountain. With all this material coming out, they can grow thousands of meters tall. As we ve seen with the famous Mount Saint Helens, composite volcanoes can explode violently.
Shield These are large, broad volcanoes that look like shields from above. The lava that pours out of shield volcanoes is thin, so it can travel for great distances down the shallow slopes of the volcano. These volcanos build up slowly over time, with hundreds of eruptions, creating many layers. They re not likely to explode catastrophically. Perhaps the best known shield volcanoes are the ones that make up the Hawaiian Islands.
Lava Dome Volcanic or lava domes are created by small masses of lava which are too thick to flow very far. Unlike shield volcanoes, with low-viscosity lava, the magma from volcanic domes just pile up over and around the vent. The dome grows by expansion of the lava within, and the mountain forms from material spilling off the sides of the growing dome. Lava domes can explode violently, releasing a huge amount of hot rock and ash.
Signs of a volcanic eruption Small earthquakes near a volcano Inflation Swelling Increased emission of heat and gas from vents
Lava Lava is the molten rock expelled by a volcano during an eruption. The resulting rock after solidification and cooling is also called lava. The molten rock is formed in the interior of some planets and some of their satellites. The source of the heat that melts the rock within the earth is geothermal energy. When first erupted from a volcanic vent, lava is a liquid usually at temperatures from 1,292 to 2,192 F.
Tephra (Ash) Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size or emplacement mechanism.
Pyroclastic Flow A dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at great speed.
Lahar A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. Lahars are extremely destructive. They can flow at speeds of 22 mph or more, be 460 ft deep, and will destroy any structures in their path.
Volcanic Gas Volcanic gases include a variety of substances given off by active volcanoes (sometimes dormant/sleepy ones too). These include gases trapped in cavities/holes in volcanic rocks, dissolved or separated gases in magma and lava, or gases being released directly from lava or indirectly through groundwater heated by volcanic action. Sources of volcanic gases on Earth Ancient and recycled elements from the Earth's mantle Absorbing elements from the Earth's crust Groundwater and the Earth's atmosphere
Dangerous Effects Volcanic eruptions can cause earthquakes, flash floods, mud slides, and rock falls. Lava can travel very far and burn, bury, or damage anything in its path, including people, houses, and trees. The large amount of dust and ash can cause roofs to fall, makes it hard to breathe, and can block out the sun. Volcanoes can also cause big earthquakes and tsunamis.
Stay out of the area defined as a restricted zone by government officials How to stay safe around volcanoes Be prepared for the hazards that can accompany volcanoes Make evacuation plans Develop an emergency communication plan Have disaster supplies on hand Follow the evacuation order issued by authorities Avoid areas downwind and river valleys downstream of the volcano Protect yourself from ash