eruption styles - Styles of Eruptions Styles of Eruptions...

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Unformatted text preview: Styles of Eruptions Styles of Eruptions and Volcanic Hazards Styles of volcanic eruptions Styles of volcanic eruptions Some volcanoes may erupt only once Some - monogenetic (Diamond Head) monogenetic Other volcanoes erupt many times Other polygenetic (Kilauea) polygenetic Some erupt very gently (Kilauea) Others are very violent and explosive Others (Mt. St. Helens, Mt. Pinatubo) (Mt. How come? Explosive volcanoes found Explosive volcanoes found associated with subduction zones Explosiveness is a function of magma Explosiveness viscosity (resistance to flow) (resistance Magmas that generate the explosive Magmas volcanoes are much more viscous than the non-explosive magmas than More silica, cooler magma, more gas Hawaiian magmas Hawaiian magmas Not very explosive Not very viscous Low silica, hot magma, moderate gas content Eruptive styles are Eruptive styles are Classified by level of eruption Classified explosiveness explosiveness I. Flood eruptions I. Flood eruptions Least explosive eruptions Least Very fluid basalt erupted in very large Very quantities VERY FAST VERY Lavas erupted over large areas Thought to develop as hot spots burn Thought thru crust thru Columbia Plateau More than 420,000 cubic km of lava Flood basalts II. Hawaiian-type eruptions Hawaiian­type eruptions Hawaiian­type eruptions The next least explosive kind of The eruption eruption Fluid magmas with small amounts of Fluid gas gas Eruptions relatively gentle Periodically have a violent eruption but Periodically very rare - Drive in volcanoes Drive Hawaiian-type eruptions Build shield volcanoes Surtseyan Fragmentation (grain size) phreatoplinian Peléan Vulcanian Strombolian Plinian Intensity (dispersal) Modified from Julia Sable Styles of explosive volcanism Styles of explosive volcanism III. Strombolian eruptions III. Strombolian eruptions Named for volcanic island off coast of Italy Characterized by less fluid lavas Moderate explosive activity Tephra common Lots of ash blankets country side Basalt and andesite common Basalt Large steep-sided composite volcanoes built by Large repeated Strombolian eruptions repeated More explosive eruptions Build composite cones Mt. Shasta, California ‘A’a flows IV. Vulcanian eruptions IV. Vulcanian eruptions Characterized by more viscous lavas “Stubbly” flows are common Stubbly” Lots of ash Andesite most common Arenal Volcano, Costa Rica V. Peléan eruptions V. Pel Named for 1902 eruptions of Mount Named Pelée on Martinique in the Caribbean Caribbean Mt. Pelé Mt. Pel eruption Almost 30,000 people were killed instantly instantly Peléan eruptions Pel Lavas highly viscous, very explosive Lavas Explosive eruption of highly gas-charged Explosive lava leads to nuée ardente (glowing nuée avalanche) or pyroclastic flow which move at 60+ kph and are 300deg C inside 60+ 300 Don’t outrun these guys!!! Pyroclastic flows formed during 1968 eruption of Mt. Mayon Ash cloud is 30,000 ft high Flows caused by ash cloud collapse or lava dome collapse VI. Plinian Eruption VI. Plinian Eruption most powerful eruption Named for Roman naturalist killed in Named explosion of Mt. Vesuvius in 79 A.D Very destructive Accompanied by major collapse Plinian Eruption Plinian Eruption Mt. St. Helens is good example before during Plinian = most powerful eruption Plinian = most powerful eruption Crater Lake in Oregon formed by similar Crater explosive eruption explosive Ash from this volcano (Mt. Mazama) Ash found all over the Pacific Northwest & as far east as the Mississippi River! as Plinian = most powerful eruption Greatest Plinian eruptions of modern Greatest times: 1813 explosion of Tambora volcano 1813 (eastern Indonesia) 1883 explosion of Krakatau (Sunda 1883 Strait between Java and Sumatra) Strait Explosion Explosion heard in northern Australian, 2400 km away 2400 Other Recent Eruptions Other Recent Eruptions Pinatubo = Vulcanian-type eruption Mt. Unzen (Japan,1991) -- generated a number of lava domes that collapsed, sending pyroclastic flows down the side of the volcano, so it can be classified as a Peléan eruption Peléan Volcanoes & Plate Tectonics Volcanoes & Plate Tectonics OK. So, where do you find all these OK. volcanic eruptive styles? volcanic Flood eruptions - atop hot spots Hawaiian - at hot spots & along MOR All the rest are associated with subduction! subduction Fragmentation (grain size) Surtseyan phreatoplinian Peléan Vulcanian Strombolian Plinian Intensity (dispersal) Styles of explosive volcanism Styles of explosive volcanism What are the hazards? Volcanic Volcanic Hazards 1. Lava 1. Lava Flows Volcanic Hazards Volcanic Hazards 2. Falling Tephra 2. Falling Like one sees at the Like beginning of the movie Dante’s Peak. movie Falling tephra in Yakima, Washington Falling during Mt. St. Helens eruption More Volcanic Hazards More Volcanic Hazards Pyroclastic flows Mudflows - Lahars Toxic volcanic gases Hazards in Hawaii Hazards in Hawaii Lava flows Lava Note: The next few slides are courtesy of G&G graduate student Chris Gregg Lava Flow Hazard Zone Map of Hawaii Historic Eruptions Mauna Loa: 33 flows since 1843 5 reached ocean in Kona Hualalai: 3 flows since ~1800 2 reached ocean in Kona High effusion rates: 3-12 x 106 m3 day -1 Steep slopes > 6 %: Hualalai: >50 % Mauna Loa: 35 % Kilauea: <5 % Fast transit times: < 24 24 hours hours 1877 Lava Flows Lava Flows From Hualalai and Mauna Loa That Have Affected Kailua­Kona Resorts Airport Subdivision Hualalai’s last eruptions (c. 1800­1801) Hualalai’s last eruptions (c. 1800­1801) MAUNA LOA’s Radial Vents (33) and Rift Zones Historic radial vent eruptions: 1843, 1859, 1877, 1935 Typical Mauna Loa Eruptions: Summit followed by fissure eruptions What Controls the Flow Paths of Lava Flows? Topography What Controls the Speed of Lava Flows? Slope angle, surface roughness, eruption rate, lava type (viscosity) 1950 Eruption: Flow velocities 16-48 km/hr Note that all of these hazards are associated with the big island! How come? Ash covers sides of volcano Ash Ash becomes unstable during heavy Ash rain rain Ash mud flow - LAHARS Ash LAHARS 10 years+ after Pinatubo eruption, 10 mudflows were still killing people mudflows Worst volcanic hazards often Worst volcanic hazards often occur after major eruptions LAHAR - ASH MUD FLOW LAHAR Volcanic gases Volcanic gases Very dangerous Very CO , CO, SO , H S, HCl and HF 2 2 2 Hawaiian volcanoes Hawaiian volcanoes Do not usually emit enough gas to Do harm people harm Except for Vog which forms as Except Vog volcano erupts and as lava enters the ocean (Even reaches O`ahu with Kona wind) Kona Attempts to control flows Attempts to control flows In the past, people have tried to control, In direct lava flows by: direct Diverting the flow with barriers built with Diverting barriers bulldozers bulldozers Diverting by bombing one or all of the Diverting bombing following locations - the vent, edge of a flow, tube entrance tube Water the flow front - not very successful! Avoiding volcanic hazards Avoiding volcanic hazards Predict them Volcanologists getting good at predicting Volcanologists eruptions of dangerous volcanoes eruptions Mt. St. Helens, Unzen and Pinatubo But, missed 1993 Mayon eruption But, Predictions eruptions Predictions eruptions Mostly Mostly made based on monitoring: monitoring Seismic activity increases Ground tilting Increased heat flow Increase in %sulfur in volcanic gas Because Because magma is moving into shallow levels under volcano! shallow Cyclic nature of Kilauea eruptions Wai`anae Volcano Ko`olau Volcano Thurston Lava Tube Meteorites have struck the Earth in the past. Many meteorites are made of iron and nickel. We think this represents material of planets similar to Earth. Earth’s interior (core) is probably also composed of iron and nickel. The end! The end! ...
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