Volcanology: Types of Volcanoes and Their Characteristics, Study notes of Art

Download Volcanology: Types of Volcanoes and Their Characteristics and more Study notes Art in PDF only on Docsity! The Science Behind Volcanoes A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, volcanic ash and gases to escape from the magma chamber below the surface. Volcanoes are generally found where tectonic plates are diverging or converging. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by convergent tectonic plates coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the Earth's crust in the interiors of plates, e.g., in the East African Rift, the Wells Gray-Clearwater volcanic field and the Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "Plate hypothesis" volcanism. Volcanism away from plate boundaries has also been explained as mantle plumes. These so- called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle boundary, 3,000 km deep in the Earth. Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. Volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere. Historically, so-called volcanic winters have caused catastrophic famines. 4 Types of Volcanoes 1.) Shield Volcano (largest volcanoes)  Profile: large size and gentle slope, resembles a warriors shield  Lava: highly fluid lava eruptions, travels far and spreads quickly and thinly  Viscosity: low viscosity magma  Silica Content: 50%  Rock Type: basalt, high levels of sodium, potassium and aluminum  Examples: Hawaiian Islands: Mt. Kilaeua, Mauna Loa, Galapagos Islands http://en.wikipedia.org/wiki/Shield_volcano 2.) Stratovolcanoes (most common type, some are also composite volcanoes)  Profile: steep profiles and slopes, and periodic explosive eruptions  Lava: thick, viscous lava and rock rubble Mauna Loa, Hawaii  Viscosity: intermediate viscosity  Silica Content: 60-64%  Rock Type: andesite  Examples: Mount St. Helens, Mount Fuji, Krakatoa & Vesuvius—destroying town of Pompeii and Herclaneum in 79 AD http://en.wikipedia.org/wiki/Stratovolcano 3.) Cinder Cones  Profile: steep conical hill made of tephra (pyroclastic debris), bowl-shaped crater at summit, common on flanks of shield and stratovolcanoes  Lava: first explosive eruption, then quiet, oozy lava with small amounts of gas  Viscosity: intermediate-high viscosity  Silica Content: 63-68%  Rock Type: dacite, andecite  Examples: Lava Butte, Oregon; Mount Fox, Australia http://en.wikipedia.org/wiki/Cinder_cone 4.) Lava Domes  Profile: rough, circular mound-shaped protrusion (a structural element in many stratovolcanoes)  Lava: slow extrusion, extremely thick viscous lava, does not flow far from the vent Mt. Fuji, Japan Cinder Cone at Little Lake, California Texture: Lava at Mount Rainier is not as fluid as lava at the volcanoes on Hawai'i, where lava flows sometimes resemble hot molasses, nor is it as viscous as lava at Mount St. Helens. Tephra: fragmental material produced by a volcanic eruption regardless of composition, fragment size or emplacement mechanism. Also referred to as pyroclasms (airborne), and pyroclastic flows (on ground) and rocks. Tephra can stay in the stratosphere for days to weeks following an eruption. It can also reflect light and heat from the sun back into the atmosphere. Tephra mixed with precipitation can also be acidic and cause acidic rain and snowfall. Tephra is made up of ash (fragments of pulverized rock, minerals and volcanic glass), volcanic blocks (a mass of molten rock), and lapilli (little broken up pieces of molten or semi-molten lava ejected from eruption). Other Types of Volcanic Rock If a rhyolite lava flow cools quickly, it can quickly freeze into a black glassy substance called obsidian. When filled with bubbles of gas, and usually with explosive eruptions, the same lava will form pumice. If the same lave is allowed to cool slowly…it will form a light-colored, uniformly solid rock called rhyolite. Pumice most commonly forms with rhyolite lava flows, though it has formed from dacite and andacite flows as well. Pumice is so lightweight, it will float on water Obsidian has been used for centuries in many countries for things such as weapons and art. Utah Volcanoes 1.) Sheild Volcanoes: Cedar Hill, Box Elder County (1,150,000 years old) Sheild volcanoes started to erupt about 12 million years ago after plate motions and resulting crustal forces changed. Compressional forces had eased and the crust started to stretch between the Wasatch Rang in Utah and the Sierra Nevada Range in California. This extension created splintered zones in the Earth’s crust where magma rose to the surface creating shield volcanoes and cinder cones. 2.) Stratovolcano: Mount Belknap, Tushar Mountains, Paiute County & Monroe Peak on the Sevier Plateau. Stratovolcanoes erupted in western Utah between 40-25 million years ago. At this time Utah was closer to a continental-oceanic plate boundary, where the oceanic plate was subducting undearneath the North American continental plate. Now active volcanoes are located in the Cascade Range of Washington, Oregon and California. 3.) Cinder Cone: Diamond Cinder Cone, Washington County (27K years old) 4.) Santa Clara, North of St. George, Dormant The Santa Clara volcanic field is volcanic area north of St. George in SW Utah, which has been active since abaout 4 million years ago. It contains numerous cinder cones and lava flows. The Santa Clara lava flow was erupted from 2 young cider cones above Snow Canyon about 10-20,000 years ago and is one of the youngest lava flows in the Colorado Plateau/Basin and Range region. The almost unvegetated lava flow extends 16 km to the south down Snow Canyon, excavated through rocks of the colorful Navajo Sandstone. 5.) Kolob Volcano, Zion National Park, Extinct (probably) Kolob is a volcanic field in Zion National Park, Utah. It contains a chain of cinder cones and lava flows, the youngest one being the cinder cones in Diamond Valley. Other famous features of the area include the Kolob Canyons, Kolob Plateau, and Kolob Arch. 6.) Markagunt Plateau Volcano, Dixie National Forest, Dormant The Markagunt Plateau volcanic field, located east of Cedar Breaks National Monument in SW Utah, is a group of cinder cones and lava vents on Markagunt Plateau. The youngest cinder cones are located near Panguitch Lake in the north and Navajo Lake in the south. Volcanic activity on the eastern Markagunt Plateau began about 5 million years ago and has been continuing up to the last eruption, which occurred only about 1,000 years ago. The date was obtained by dendrochronology, i.e. by counting the growth rings and thus, the age, of the oldest trees on the flow. A common maximum age of 900 years for the oldest present trees (big gnarled junipers (/. scapularium)) was found, which suggests the age of the flow being only about 1000 years old, if the first trees appeared to grow 100 years after the flow was emplaced. Eruptions in the Markagunt Plateau field have produced basaltic flows at Miller Knoll, Cooper Knoll, and Henry Peaks, Duck Creek, at Bowers Flat, in Black Rock and in the upper Rock Creek valleys. The oldest episodes of volcanic activity produced silica-rich trachytic, andesitic and rhyolitic lavas, and were followed by extensive basaltic lavas occuring in 2 different ages. Several lines of NE-SW-trending cinder