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Volcanoes and the Frequency and Style of Their Eruptions (A Geological Problem)

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Volcanoes and the Frequency and Style of Their Eruptions (A Geological Problem) Prediction of Volcanic Eruptions Vo s l c e Long Term Prediction a no Identify volcanoes and the frequency and style of their eruptions (a geological problem). Establish probabilities of eruption, style and location for Part II individual volcanoes. Prediction Establish the level of risk based on historic and geologic Impact of eruptions record. Supervolcanoes E.g., for individual volcanoes: determine most likely routes Volcanoes in space for lahars, nuees ardentes, lava flows, etc., and avoid construction in those areas. Hazard zones have been distinguished around Mt. Shasta Hazard zones have been distinguished around Mt. Shasta based on topography and past experience with eruptions. based on topography and past experience with eruptions. Zone 1: areas likely to be affected Zone 1: areas likely to be affected Zone 1 most frequently. Most future flows Zone 2 most frequently. Most future flows from summit eruptions probably from summit eruptions probably would stay within this zone. would stay within this zone. Zone 2: areas likely to be affected by lava flows erupted from vents on the flank of the volcano or that move into zone 2 from zone 1. Short-term prediction Hazard zones have been distinguished around Mt. Shasta based on topography and past experience with eruptions. Based on the recognition of a pattern of events prior to Zone 1: areas likely to be affected previous eruptions. Zone 3 most frequently. Most future flows from summit eruptions probably Gas emissions: rates of emission and type of gas changes in would stay within this zone. some volcanoes. Zone 2: areas likely to be affected Important gases include sulfur dioxide (SO2) and carbon by lava flows erupted from vents dioxide (CO ) on the flank of the volcano or that 2 move into zone 2 from zone 1. Changes in concentration may reflect movement of the Zone 3: areas likely to be affected magma up the vent. infrequently and then only by long lava flows that originate at vents in zones 1 and 2 1 Surface tilting: recognition of changes in the land Earthquakes: generated as the magma moves up the surface due to building pressure in the conduit. feeder conduit to the vent. A surface bulge appeared on Mt. St. Helens prior to its eruption. When viscous magma becomes stuck in the conduit strain April 8, 1980 energy builds as more magma tries to push out. Movement takes place in a series of “jerks” as the rock material breaks. Each “jerk” produces an earthquake. Magnitudes generally less than 5 M. April 26 May 2 The more earthquakes the further the magma has moved. Mount Spurr, Alaska: The 1992 Eruption of Crater Peak Vent A combination of approaches is likely the key to short-term prediction. Black bars: earthquake USGS frequency. Red lines: volcanic eruptions. The impact of volcanic eruptions Volcanic Hazards Lava flows Commonly destroy property in Hawaii and Iceland. Damage limited to the vicinity in the immediate area of the volcano. Fatalities rare due to slow speed of advancing lava flow. 2 Ash fall An ashfall 10 million years ago killed these rhinos that are preserved at Ashfall Fossil Beds State Historic Park, Nebraska. Extensive property damage and fatalities can result from heavy ash falls. Death was not by burial but by lung failure due to inhaling the ash. Significant ash in the upper atmosphere can circle the globe in a matter of weeks. More than 80 commercial jets have been damaged by flying through volcanic ash clouds. Mt. St. Helens’ ash cloud Pyroclastic flows Lahars can be the most devastating outcome of many volcanoes. Lahars are fast moving mudflows that can inundate urban areas that are nearby the eruption. A relatively small eruption of Nevada del Ruiz, Columbia, in 1985, generated a lahar when the volcano melted a 2.5 km2 area of snow and ice. Lahars can also dam rivers and which can lead to extensive flooding. Water and debris rushed down the slopes, picking up more debris along the way. A 5 metre wall of water and debris Nuée ardentes destroy life and property in their paths. slammed into the town of Amero, 72 km from the volcano. 60 people, thousands of animals and fish, and hundreds of acres of lumber were destroyed by ash flows from Mt. St. Helens. A Nuée Ardent killed 20,000 people when Mt. Vesuvius The lahar killed exploded and shed a pyroclastic flow across the village 28,700 people and of Pompeii in 79 AD. destroyed over 5,000 structures in the city. 3 Landslides People and animals Landslides can be generated when a volcano collapses died instantly from the during an eruption. rushing cloud of hot gas and ash. During the Mt. St. Helens eruption 2.3 km3 of debris slid down the mountain at speeds up to 240 km/hr. The slide traveled over 24 km and left a 45 m deep deposit. 350,000 years ago Mt. Shasta experienced a similar eruption and landslide that was 20 times greater than that of Mt. St. Helens. Volcanic Gases SO2 emissions can have direct effects on life in the vicinity of a volcano. In addition to making magma more explosive, volcanic eruptions also include gases that can be deadly to all life. An eruption in 1783 of Laki Crater (Iceland) produced a sulfurous haze that lasted for 9 months and killed 75% of all livestock and 24% of the Icelandic population. Volcanoes release more than 130 to 230 million tonnes of CO2 into the atmosphere every year Humans add CO2 at the rate of approximately 22 billion tonnes per year (150 times the rate of volcanic production) CO , SO and CO are the most abundant of harmful gases. 2 2 Human CO2 production is equal to that if 17,000 volcanoes like Kilauea were erupting every year. Mammoth Mountain is If the air that we breath has more than 10% CO2 it a relatively young becomes deadly because it displaces the Oxygen that we volcano that is emitting need for respiration. large volumes of CO2. Lake Nios, Cameroon, is a very deep lake within a volcanic crater. The lake is so deep that hydrostatic pressure forces CO2 to remain at the lake bottom. When the pressure of the CO2 exceeds a certain limit the Gas concentrations in the soil in gas rapidly bubbles up out of the lake and flows as an some areas near the mountain are invisible gas cloud down the adjacent slopes. high enough to kill trees and small animals. On August 61, 1986 such a gas release flowed 19 km suffocating 1,700 people along its route. 4 Tsunamis Lake Nyos 10 days after the 1986 eruption Caused by the displacement of seawater by eruptions of volcanic islands and submarine volcanoes. Krakatoa (1883 eruption) killed 36,000 people by the tsunami, alone (the most deadly outcome of the eruption). The fountain in the This is the newly forming background lifts CO 2 summit of Krakatoa, growing up to the surface so where the 1883 eruption blew that it no longer the top off of the original accumulates. volcano. Global Climate Change A series of eruptions of Tambora (Indonesia) extruded up to 150 km3 of magma (solid equivalent), much of it into the Due to ash and gas that may spend years in the upper atmosphere. atmosphere; reduces incoming solar radiation. SO2 from an eruption forms tiny droplets of sulfuric acid in the upper atmosphere. The droplets significantly increase global albedo…..a negative radiative forcing that leads to cooling. Tambora (1815 eruption) was followed in 1816 by the “year without a summer”. Mt. Pinatubo (1991) released 22 million metric tons of SO 2 Average global temperature is estimated to have been and reduced the Earth’s average temperature by 0.5 reduced by 3 degrees Celsius. degrees Celsius in the year following the eruption. In June of 1816 there was widespread snowfall throughout Approximately 260,000 people have been killed by volcanoes in the eastern United States. historic times…most by a handful of individual eruptions. The normal growing season experienced repeated frosts as cold air extended much more southerly than normal. Food shortages and starvation are attributed to the deaths of 80,000 people. The global population was about 1 billion people in 1816. Our current population is a little over 6 billion. The 1816 fatality rate would have resulted in a death toll of nearly 500,000 people due to starvation. 5 Volcanic Explosivity Index http://pubs.usgs.gov/publications/msh/comparisons.html Deadly Historic Volcanic Eruptions An eruption in 1902 following the growth of a lava dome on the side Mt. Pelée of the mountain. (West Indes) VEI = 4 Lava domes are constructed of A stratovolcano along viscous lava and are prone to the Caribbean trench. collapse, unleashing a violent pyroclastic flow. The nuée ardente that was generated when Mt. Pelée erupted swept 6 km downslope through the town of St. Vincent. 6 Tambora (1815) VEI = 7 Almost the entire population of 30,000 The largest eruption of historic time. people were killed within minutes of Greatest impacts from pyroclastic flows and inhaling the hot gases ash and gas eruptions. and ash. Approximately 150 km3 of ash was erupted with the explosions. There were only two survivors; one was in a 10,000 people were killed by bomb impacts, tephra falls and dungeon! pyroclastic flows. By far the largest impact was on the Earth’s atmosphere. The eruption plume reached 44 km above the earth, loading the stratosphere with ashes and gases. Krakatoa (1883) VEI = 6 The concentration mercury On the Island of Rakata, Krakatoa was one of in ice cores from glaciers in 130 active volcanoes in Indonesia (the country Wyoming record a peak in with the most active volcanoes in the world).
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