1 (No Transcript) 2 Volcanoes Volcanologists - have classified volcanoes into groups based on the shape of the volcano the materials they are built of and the way the volcano erupts.
Types 1. Composite Volcanoes (also called strato volcanoes)
2. Shield Volcanoes (also called shields)
3. Cinder Cones
4. Spatter Cones and
5. Complex Volcanoes (also called compound volcanoes).
3 (No Transcript) 4 Lets take a look at each type and describe them. 1. Composite Volcanoes (also called strato volcanoes) - are formed by alternating layers of lava and rock fragments. This is the reason they are called composite. - Strato-volcanoes often form impressive snow-capped peaks which are often exceeding 2500m in height 1000km2 in surface and 400km3 in volume. - Between eruptions they are often so quiet they seem extinct. - Composite volcanoes usually erupt in an explosive way. This is usually caused by viscous magma. - When very viscous magma rises to the surface it usually clogs the craterpipe and gas in the craterpipe gets locked up. - Therefore the pressure will increase resulting in an explosive eruption. 5 Composite Volcanoes (also called strato volcanoes) 6 Although strato-volcanoes are usually large and conical we can distinguish different shapes of them concave (like Agua) pyramidal (like Stromboli) convex-concave (like Vesuvius) helmet-shaped (like Mount Rainier) collapse caldera (like Graciosa) nested (like El Piton in Teide) multiple summits (like Shasta) elongated along a fissure (like Hekla). 7 Strato-volcanoes are constructed along subduction zones. Examples of composite volcanoes include Mount Hood Mount Rainier Mount Shasta Mount Fugi Mount Mayon and Vesuvius. 8 Shield volcanoes 9 Shield volcanoes Shield volcanoes are huge in size. They are built by many layers of runny lava flows. Lava spills out of a central vent or group of vents. A broad shaped gently sloping cone is formed. This is caused by the very fluid basaltic lava which cant be piled up into steep mounds. 10 Shield volcanoes may be produced by hot spots which lay far away from the edges of tectonic plates. Shields also occur along the mid-oceanic ridge where sea-floor spreading is in progress and along subduction related volcanic arcs. The eruptions of shield volcanoes are characterized by low- explosivity lava-fountaining that forms cinder cones and spatter cones at the vent. Famous shield volcanoes can be found for example in Hawaii (e.g. Mauna Loa and Kilauea). Mauna Loa This volcano is the largest one on earth. It began to form millions of years ago. The summit crater called Mokuaweoweo has walls that rise to 180 meters! Mauna Loa emits lava around very 4 years. - It is an active shield Volcano 4170 meters tall 11 (No Transcript) 12 Cinder cone A cinder cone is a steep conical hill formed above a vent. Cinder cones are among the most common volcanic landforms found in the world. They arent famous as their eruptions usually dont cause any loss of life. Cinder cones are chiefly formed by Strombolian eruptions. The cones usually grow up in groups and they often occur on the flanks of strato volcanoes and shield volcanoes. Strombolian - when the magma is viscous the locked up gas will escape intermittently when rising to the surface. Often this results in blocks and bombs which will fall on the surrounding environment 13 (No Transcript) 14 Cinder cone The cones usually grow up in groups and they often occur on the flanks of strato volcanoes and shield volcanoes. Cinder cones are built from lava fragments called cinders. The lava fragments are ejected from a single vent and accumulate around the vent when they fall back to earth. Cinder cones grow rapidly and soon approach their maximum size. They rarely exceed 250m in height and 500m in diameter. 15 A Few Volcanic Definitions to get you started aa (pronounced ah-ah) Hawaiian word used to describe a lava flow whose surface is broken into rough angular fragments composed of broken lava blocks called clinkers. A caldera is a volcanic feature formed by the collapse of a volcano into itself making it a large special form of volcanic crater. The word caldera comes from a Spanish word meaning cauldron. In volcanology a lava dome is mound-shaped growth resulting from the eruption of high-silica lava (usually rhyolite and/or dacite) from a volcano 16 A lahar is a type of mudflow composed of pyroclastic material and water that flows down from a volcano typically along a river valley. The term lahar originated in Indonesia. Pahoehoe (Hawaiian English from Hawaiian meaning smooth unbroken lava) is basaltic lava that has a smooth billowy or ropy surface. A pahoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. 17 Pillow lava is the rock type typically formed when lava emerges from an underwater volcanic vent or a lava flow enters the ocean. The viscous lava gains a solid crust immediately upon contact with the water and this crust cracks and oozes additional large blobs or pillows as more lava emerges from the advancing flow. 18 Pyroclastic rocks or tephra are deposits comprising the entire range of fragmental products deposited directly by explosive or effusive (formed by a nonexplosive outpouring of lava) volcanic eruptions Three modes of transport can be distinguished pyroclastic flow pyroclastic surge and pyroclastic fall A spatter cone is formed of molten lava ejected from a vent somewhat like taffy. 19 Basalt Plateau extensive continental deposits of basaltic volcanic rock. Complex volcano means the system of those volcanoes is not simple. Caldera complexes for instance have often got a large caldera with many subsidiary vents and deposits some of which could be considered volcanoes in their own right. A volcano that consists of a complex of two or more vents is reckoned as a compound or complex volcano. 20 More Questions from text book (paper cover 4th ed.) 1) Where do you find pillow lava and describe what it looks like 2) What is the difference between aa lava and pahoehoe lava 3) What is Volcanism 4) What are mountains 5) Why are volcanoes with lava domes considered very dangerous 6) How are calderas formed 7) How are pyroclastic sheet deposits formed 8) How do geologists evaluate/monitor volcanoes 9) Can we predict an eruption And if so how
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