\r\n| 0<\/td>\r\n | <100\u00a0m (330\u00a0ft)<\/td>\r\n | 1,000\u00a0m3<\/sup> (35,300\u00a0cu\u00a0ft)<\/td>\r\n| Hawaiian<\/td>\r\n | Continuous<\/td>\r\n | Kilauea<\/td>\r\n<\/tr>\r\n | \r\n| 1<\/td>\r\n | 100\u20131,000\u00a0m (300\u20133,300\u00a0ft)<\/td>\r\n | 10,000\u00a0m3<\/sup> (353,000\u00a0cu\u00a0ft)<\/td>\r\n| Hawaiian\/Strombolian<\/td>\r\n | Fortnightly<\/td>\r\n | Stromboli<\/td>\r\n<\/tr>\r\n | \r\n| 2<\/td>\r\n | 1\u20135\u00a0km (1\u20133\u00a0mi)<\/td>\r\n | 1,000,000\u00a0m3<\/sup> (35,300,000\u00a0cu\u00a0ft)\u2020<\/sup><\/td>\r\n| Strombolian\/Vulcanian<\/td>\r\n | Monthly<\/td>\r\n | Galeras (1992)<\/td>\r\n<\/tr>\r\n | \r\n| 3<\/td>\r\n | 3\u201315\u00a0km (2\u20139\u00a0mi)<\/td>\r\n | 10,000,000\u00a0m3<\/sup> (353,000,000\u00a0cu\u00a0ft)<\/td>\r\n| Vulcanian<\/td>\r\n | 3 monthly<\/td>\r\n | Nevado del Ruiz (1985)<\/td>\r\n<\/tr>\r\n | \r\n| 4<\/td>\r\n | 10\u201325\u00a0km (6\u201316\u00a0mi)<\/td>\r\n | 100,000,000\u00a0m3<\/sup> (0.024\u00a0cu\u00a0mi)<\/td>\r\n| Vulcanian\/Pel\u00e9an<\/td>\r\n | 18 months<\/td>\r\n | Eyjafjallaj\u00f6kull (2010)<\/td>\r\n<\/tr>\r\n | \r\n| 5<\/td>\r\n | >25\u00a0km (16\u00a0mi)<\/td>\r\n | 1\u00a0km3<\/sup> (0.24\u00a0cu\u00a0mi)<\/td>\r\n| Plinian<\/td>\r\n | 10\u201315 years<\/td>\r\n | Mount St. Helens (1980)<\/td>\r\n<\/tr>\r\n | \r\n| 6<\/td>\r\n | >25\u00a0km (16\u00a0mi)<\/td>\r\n | 10\u00a0km3<\/sup> (2\u00a0cu\u00a0mi)<\/td>\r\n| Plinian\/Ultra-Plinian<\/td>\r\n | 50\u2013100 years<\/td>\r\n | Krakatoa (1883)<\/td>\r\n<\/tr>\r\n | \r\n| 7<\/td>\r\n | >25\u00a0km (16\u00a0mi)<\/td>\r\n | 100\u00a0km3<\/sup> (20\u00a0cu\u00a0mi)<\/td>\r\n| Ultra-Plinian<\/td>\r\n | 500\u20131000 years<\/td>\r\n | Tambora (1815)<\/td>\r\n<\/tr>\r\n | \r\n| 8<\/td>\r\n | >25\u00a0km (16\u00a0mi)<\/td>\r\n | 1,000\u00a0km3<\/sup> (200\u00a0cu\u00a0mi)<\/td>\r\n| Supervolcanic<\/td>\r\n | 50,000+ years[footnote]Dosseto, A., Turner, S. P. and Van-Orman, J. A. (editors) (2011). Timescales of Magmatic Processes: From Core to Atmosphere<\/em>. Wiley-Blackwell. See also Rothery, David A. (2010). Volcanoes, Earthquakes and Tsunami<\/em>s. Teach Yourself.[\/footnote]<\/td>\r\n| Lake Toba (74 ka)<\/td>\r\n<\/tr>\r\n | \r\n| <\/span>*<\/b> This is the minimum eruptive volume necessary for the eruption to be considered within the category.\r\n<\/span>**<\/b> Values are a rough estimate. They indicate the frequencies for volcanoes of that magnitude OR HIGHER\r\n<\/span>\u2020<\/b> There is a discontinuity between the 1st and 2nd VEI level; instead of increasing by a magnitude of 10, the value increases by a magnitude of 100 (from 10,000 to 1,000,000).<\/small><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n | | | | | | | | | | |
![\"Mosaic](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06180129\/Lava_forms.jpg\")
Figure 1. Some of the eruptive structures formed during volcanic activity: a Plinian eruption column, Hawaiian pahoehoe flows, and a lava arc from a Strombolian eruption.[\/caption]\r\n\r\nSeveral types of<\/b> volcanic eruptions<\/b>\u2014during which lava, tephra (ash, lapilli, volcanic bombs and blocks), and assorted gases are expelled from a volcanic vent or\u00a0fissure\u2014have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.\r\n\r\nThere are three different types of eruptions. The most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruptions are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity. The third eruptive type is the phreatic eruption, which is driven by the superheating of steam via contact with magma; these eruptive types often exhibit no magmatic release, instead causing the granulation of existing rock.\r\n\r\nWithin these wide-defining eruptive types are several subtypes. The weakest are Hawaiian and submarine, then Strombolian, followed by Vulcanian and Surtseyan. The stronger eruptive types are Pelean eruptions, followed by Plinian eruptions; the strongest eruptions are called \"Ultra-Plinian.\" Subglacial and phreatic eruptions are defined by their eruptive mechanism, and vary in strength. An important measure of eruptive strength is Volcanic Explosivity Index (VEI), an order of magnitude scale ranging from 0 to 8 that often correlates to eruptive types.\r\n![\"Volcanic](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06180411\/VEIfigure_en.svg_.png\")
Figure 2. Diagram showing the scale of VEI correlation with total ejecta volume.[\/caption]\r\n\r\nVolcanic eruptions arise through three main mechanisms:[footnote]Heiken, G. and Wohletz, K. Volcanic Ash<\/i>. University of California Press. p.\u00a0246.[\/footnote]\r\n![\"Scheme](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06192907\/Hawaiian_Eruption-numbers.svg_.png\")
Figure 3. Diagram of a Hawaiian eruption. (key: 1. Ash plume 2. Lava fountain 3. Crater 4. Lava lake 5. Fumaroles 6. Lava flow 7. Layers of lava and ash 8. Stratum 9. Sill 10. Magma conduit 11. Magma chamber 12. Dike) Click for larger version.[\/caption]\r\n\r\nHawaiian eruptions are a type of volcanic eruption, named after the Hawaiian volcanoes with which this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption of very fluid basalt-type lavas with low gaseous content. The volume of ejected material from Hawaiian eruptions is less than half of that found in other eruptive types. Steady production of small amounts of lava builds up the large, broad form of a shield volcano. Eruptions are not centralized at the main summit as with other volcanic types, and often occur at vents around the summit and from fissure vents radiating out of the center.[footnote]\"How Volcanoes Work: Hawaiian Eruptions.\"\u00a0San Diego State University![\"Close](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06193017\/Ropy_pahoehoe.jpg\")
Figure 4. Ropey pahoehoe lava from Kilauea, Hawai\u02bbi.[\/caption]\r\n\r\nFlows from Hawaiian eruptions are basaltic, and can be divided into two types by their structural characteristics. Pahoehoe lava is a relatively smooth lava flow that can be billowy or ropey. They can move as one sheet, by the advancement of \"toes,\" or as a snaking lava column. A'a lava flows are denser and more viscous then pahoehoe, and tend to move slower. Flows can measure 2 to 20\u00a0m (7 to 66\u00a0ft) thick. A'a flows are so thick that the outside layers cools into a rubble-like mass, insulating the still-hot interior and preventing it from cooling. A'a lava moves in a peculiar way\u2014the front of the flow steepens due to pressure from behind until it breaks off, after which the general mass behind it moves forward. Pahoehoe lava can sometimes become A'a lava due to increasing viscosity or increasing rate of\u00a0shear, but A'a lava never turns into pahoehoe flow.[footnote]\"How Volcanoes Work: Basaltic Lava.\"\u00a0San Diego State University![\"Scheme](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06194441\/Strombolian_Eruption-numbers.svg_.png\")
Figure 5. Diagram of a Strombolian eruption. (key: 1. Ash plume 2. Lapilli 3. Volcanic ash rain 4. Lava fountain 5. Volcanic bomb 6. Lava flow 7. Layers of lava and ash 8. Stratum 9. Dike 10. Magma conduit 11. Magma chamber 12. Sill) Click for larger version.[\/caption]\r\n\r\nStrombolian eruptions are a type of volcanic eruption, named after the volcano Stromboli, which has been erupting continuously for centuries.[footnote]\"How Volcanoes Work: Strombolian Eruptions.\"\u00a0San Diego State University![\"Eruption](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06194542\/Stromboli_Eruption.jpg\")
Figure 6. An example of the lava arcs formed during Strombolian activity. This image is of Stromboli itself.[\/caption]\r\n\r\nStrombolian eruptions eject volcanic bombs and lapilli fragments that travel in parabolic paths before landing around their source vent. The steady accumulation of small fragments builds cinder cones composed completely of basaltic pyroclasts. This form of accumulation tends to result in well-ordered rings of tephra.[footnote]\"How Volcanoes Work: Strombolian Eruptions.\"\u00a0San Diego State University![\"Scheme](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06194714\/Vulcanian_Eruption-numbers.svg_.png\")
Figure 7. Diagram of a Vulcanian eruption. (key: 1. Ash plume 2. Lapilli 3. Lava fountain 4. Volcanic ash rain 5. Volcanic bomb 6. Lava flow 7. Layers of lava and ash 8. Stratum 9. Sill 10. Magma conduit 11. Magma chamber 12. Dike)[\/caption]\r\n\r\nVulcanian eruptions are a type of volcanic eruption, named after the volcano Vulcano.[footnote]\"How Volcanoes Work: Vulcanian Eruptions.\"\u00a0San Diego State University![\"Tuvurvur](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06194828\/Tavurvur_volcano_edit-e1465242544296.jpg\")
Figure 8. Tavurvur in Papua New Guinea erupting.[\/caption]\r\n\r\nVolcanoes that have exhibited Vulcanian activity include:\r\n![\"Scheme](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06194954\/Pelean_Eruption-numbers.svg_.png\")
Figure 9. Diagram of Pel\u00e9an eruption. (key: 1. Ash plume 2. Volcanic ash rain 3. Lava dome 4. Volcanic bomb 5. Pyroclastic flow 6. Layers of lava and ash 7. Stratum 8. Magma conduit 9. Magma chamber 10. Dike)[\/caption]\r\n\r\nPel\u00e9an eruptions (or nu\u00e9e ardente) are a type of volcanic eruption, named after the volcano Mount Pel\u00e9e in Martinique, the site of a massive Pel\u00e9an eruption in 1902 that is one of the worst natural disasters in history. In Pel\u00e9an eruptions, a large amount of gas, dust, ash, and lava fragments are blown out the volcano's central crater,[footnote]Cain, Fraser. \"Pelean Eruption.\"\u00a0Universe Today![\"Part](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06195620\/eruptions-1024x280.jpg\")
Figure 10. (a) Mount Lamington following the devastating 1951 eruption. (b) The lava spine that developed after the 1902 eruption of Mount Pel\u00e9e. (c) Pyroclastic flows at Mayon Volcano, Philippines, 1984.[\/caption]\r\n![\"Scheme](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06195958\/Plinian_Eruption-numbers.svg_.png\")
Figure 11. Diagram of a Plinian eruption. (key: 1. Ash plume 2. Magma conduit 3. Volcanic ash rain 4. Layers of lava and ash 5. Stratum 6. Magma chamber)[\/caption]\r\n\r\nPlinian eruptions (or Vesuvian) are a type of volcanic eruption, named for the historical eruption of Mount Vesuvius in 79 of Mount Vesuvius that buried the Roman\u00a0towns of Pompeii and Herculaneum and, specifically, for its chronicler Pliny the Younger.[footnote]\"How Volcanoes Work: Plinian Eruptions.\"\u00a0San Diego State University![\"Ascending](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06200105\/MtRedoubtedit1.jpg\")
Figure 12. 21 April 1990 eruptive column from Redoubt Volcano, as viewed to the west from the Kenai Peninsula.[\/caption]\r\n\r\nThese highly explosive eruptions are associated with volatile-rich dacitic to rhyolitic lavas, and occur most typically at\u00a0stratovolcanoes. Eruptions can last anywhere from hours to days, with longer eruptions being associated with more felsic\u00a0volcanoes. Although they are associated with felsic magma, Plinian eruptions can just as well occur at basaltic volcanoes, given that the magma chamber differentiates and has a structure rich in silicon dioxide.[footnote]\"How Volcanoes Work: Plinian Eruptions.\"\u00a0San Diego State University![\"An](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06200217\/Armero_aftermath_Marso.jpg\")
Figure 13. Lahar flows from the 1985 eruption of Nevado del Ruiz, which totally destroyed the town of Armero in Colombia.[\/caption]\r\n\r\nMajor Plinian eruptive events include:\r\n![\"The](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06200349\/Types_of_volcanoes_and_eruption_features-1024x280.jpg\")
<\/a> Figure 14. The image correlates types of volcanoes with their respective eruption, highlighting the differences. Click to view a larger version.[\/caption]\r\n![\"Scheme](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06200502\/Surtseyan_Eruption-numbers.svg_.png\")
Figure 15. Diagram of a Surtseyan eruption. (key: 1. Water vapor cloud 2. Compressed ash 3. Crater 4. Water 5. Layers of lava and ash 6. Stratum 7. Magma conduit 8. Magma chamber 9. Dike)[\/caption]\r\n\r\nA Surtseyan eruption (or hydrovolcanic) is a type of volcanic eruption caused by shallow-water interactions between water and lava, named so after its most famous example, the eruption and formation of the island of Surtsey off the coast of Iceland in 1963. Surtseyan eruptions are the \"wet\" equivalent of ground-based Strombolian eruptions, but because of where they are taking place they are much more explosive. This is because as water is heated by lava, it flashes in steam and expands violently, fragmenting the magma it is in contact with into fine-grained ash. Surtseyan eruptions are the hallmark of shallow-water volcanic oceanic islands, however they are not specifically confined to them. Surtseyan eruptions can happen on land as well, and are caused by rising magma that comes into contact with an aquifer\u00a0(water-bearing rock formation) at shallow levels under the volcano.[footnote]\"How Volcanoes Work: Hydrovolcic Eruptions.\"\u00a0San Diego State University![\"A](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06200948\/Surtsey_eruption_1963-1024x335.jpg\")
Figure 16. (a) Surtsey, erupting 13 days after breaching the water. A tuff ring surrounds the vent. (b) The fissure formed by the 1886 eruption of Mount Tarawera, an example of a fracture zone eruption.[\/caption]\r\n![\"Scheme](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06201052\/Submarine_Eruption-numbers.svg_.png\")
Figure 17. Diagram of a Submarine eruption. (key: 1. Water vapor cloud 2. Water 3. Stratum 4. Lava flow 5. Magma conduit 6. Magma chamber 7. Dike 8. Pillow lava)[\/caption]\r\n\r\nSubmarine eruptions are a type of volcanic eruption that occurs underwater. An estimated 75% of the total volcanic eruptive volume is generated by submarine eruptions near mid ocean ridges alone, however because of the problems associated with detecting deep sea volcanics, they remained virtually unknown until advances in the 1990s made it possible to observe them.[footnote]Chadwick, Bill (10 January 2006). \"Recent Submarine Volcanic Eruptions.\"\u00a0Vents Program<\/i>. NOAA![\"Scheme](\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/115\/2016\/06\/06201156\/Subglacial_Eruption-numbers.svg_.png\")
Figure 18. A diagram of a Subglacial eruption. (key: 1. Water vapor cloud 2. Crater lake 3. Ice 4. Layers of lava and ash 5. Stratum 6. Pillow lava 7. Magma conduit 8. Magma chamber 9. Dike)[\/caption]\r\n\r\nSubglacial eruptions are a type of volcanic eruption characterized by interactions between lava and ice, often under a glacier. The nature of glaciovolcanism dictates that it occurs at areas of high latitude and high altitude.[footnote]\"Glaciovolcanism\u2014University of British Columbia.\"\u00a0University of British Columbia