Volcanic Hazards in Latin America: Nueé Ardentes & pujana/latin/PDFS/Lecture 15 - L A Volcanic Haz.pdf ·…

  • Published on

  • View

  • Download


Volcanic Hazards in Latin America: NueArdentes & LaharsCircum-Pacific Ring of FireThis Dynamic Earth http://pubs.usgs.gov/publications/text/fire.htmlCould also be called Circum-Pacific Ring of EarthquakesSubduction Zone beneath W.Latin America & Lesser AntillesSeismogenic ZoneEarthquakes occur all along the subduction zone but those along the Seismogenic zone are most destructiveFlat Slab regions allow for more stress to build up between the plates(Gutscheret al., 2000)Normal (Steep) SlabFlat SlabFlat Slab segments lack arc volcanoes Andes N. Volcanic ZoneAndes Central Volcanic ZoneAndes S. Volcanic ZoneLesserAntillesIsland ArcCentralAmericaTrans-Mexico Volcanic BeltFSFSFSFlat Slab segments in S. America(Gutscheret al., 2000)Top 5 Killer Volcanic Eruptions, WorldSince 1500AD, about 300,000 people have died as a result of volcanic eruptionsVolcano Country Year # deaths Cause 1) Tambora Indonesia 1815 92,000 Starvation2) Krakatau Indonesia 1883 36,000 Tsunami3) Mt. Pele Martinique 1902 29,000 Pyroclastic flow 4) Nevado del Ruiz Colombia1985 25,000 Mudflow5) Unzen Japan 1792 15,000 Debris avalancheDeadliest eruptions in Latin AmericaVolcano Country Year DeathsNevado del Ruiz Colombia 1845 1,000Cotopaxi Ecuador 1877 >300Soufrire St. Vincent (L. Ant.) 1902 1,680Mount Pele Martinique (L. Ant.) 1902 29,000Santa Maria Guatemala 1902 ~1,500El Chichn Mexico 1982 >2,000Nevado del Ruiz Colombia 1985 25,000http://volcanoes.usgs.gov/Hazards/Effects/Fatalities.htmlMartinique, 1902Martinique, Lesser Antilles 1902http://www.mount-pelee.com/arcvolc.htmVolcanoes of the Lesser AntillesMartiniqueColonized by France in 1635, the island has subsequently remained a French possession except for three brief periods of foreign occupation. 1100 sq. km (424 sq mi.)430,000 peopleHighest point is Mt. Pelee, 1400 mhttp://www.mount-pelee.com/martinique.htmSt. PierrePrcheur *M.R.M.R. = Morne RougeSt. Pierre before 1902 eruption 2002Pre-1902http://www.mount-pelee.com/martinique.htmSt. Pierre before its Destructionhttp://www.mount-pelee.com/martinique.htmSt. Pierre was the economic center of MartiniquePelee chronologyDuring the year 1889, the reactivation of fumaroles is reported at the summit.In February 1902, strong sulfur smells are perceived, first in the vicinity of Prcheur, then in Fond Cor(North Saint-Pierre).April 1902 April 22nd, the telegraph cable between Martinique and Guadeloupe is broken. April 24th, a column of black smoke arises from the crater, up to a height of 1600-1900 ft. April 25th, the village of Prcheur is covered with ash. April 28th, strong rumblings are heard, as the vapor column becomes higher.Pelee Chronology (contd.)May 1902 May 2nd, abundant ashfalls and dull rumblings can still be heard. The black column of vapor is furrowed with lightning. The first ashfall is reported on St.Pierre, and a thin layer of dust covers the whole island. May 3rd, total darkness over Prcheur. Many inhabitants seek refuge in St. Pierre. May 5th, one of the sides of the Etang Sec Crater suddenly falls apart, giving way to a devastating mudflow which destroys the sugar mill Gurin on the coast between St.Pierre and Prcheur. The first 25 deaths are reported. May 6th, the telegraph cable between St.Pierre and St.Lucia is broken. Numerous glowing phenomena are observed over the crater. May 7th, houses collapse and trees break down under the weight of the ash.Why didnt the people of St. Pierre evacuate?No volcanologists were on the island, and for the residents the only point of reference was the mild eruption of 1851-1852. The governor appointed a "Volcano Commission" with the most qualified specialists on the island : doctors, pharmacists, science teachers... The first meeting was held May 7th (the day before the city was destroyed)First (and only) report of the St. Pierre Volcano CommissionThe commission, responsible for the study of the Mount Pele's volcanic phenomena met yesterday evening, May 7th, under the chair of the Governor. After a careful analysis of the facts, the commission declares that: 1All the phenomena which have occurred so far are normal, and are commonly observed on all volcanoes around the world; 2Since the craters of the volcano are wide open, the expansion of the vapors will continue with no earthquake or rock projection; 3According to the location of the craters and the position of the valleys leading to the sea, the City of St. Pierre is perfectly safe.Some people evacuatedSome people were afraid of the powerful phenomena which took place between April and May 7th 1902. Some families moved away from the volcano, but those voluntary evacuations were quite limited. The travel records in the early morning of May 8th - a religious holiday-- shows that there were more people traveling to St. Pierre than people leaving the city ! The story of Captain Leboffe of the Italian bark Orsolinasuggests that the population of St. Pierre would have been saved if they had some knowledge about explosive volcanoes. The Italian captain was a native of Naples, and was quite familiar with the Vesuvius volcano. He hastily left the harbor of St. Pierre on May 7th, without his custom clearance, warning that "if Vesuvius looked like Mt. Pelee did, Naples would have been evacuated"..http://www.mount-pelee.com/Ifacts.htm#HauntedTypes of Eruptions: VulcanianA vulcanian eruption is a type of explosive eruption that ejects new lava fragments that do not take on a rounded shape during their flight through the air. This may be because the lava is too viscous or already solidified. These moderate-sized explosive eruptions commonly eject a large proportion of volcanic ash and also breadcrust bombs and blocks. Andesitic and daciticmagmas are most often associated with vulcanian eruptions, because their high viscosity (resistance to flow) makes it difficult for the dissolved volcanic gases to escape except under extreme pressure, which leads to explosive behavior. http://volcanoes.usgs.gov/Products/Pglossary/vulcanian.htmlTypes of eruptions: StrombolianStrombolian eruptions are characterized by the intermittent explosion or fountaining of basaltic lava from a single vent or crater. Each episode is caused by the release of volcanic gases, and they typically occur every few minutes or so, sometimes rhythmically and sometimes irregularly. The lava fragments generally consist of partially molten volcanic bombs that become rounded as they fly through the air. The photo at right is a close view of StromboliVolcano erupting incandescent molten lava framgents. http://volcanoes.usgs.gov/Products/Pglossary/strombolian.htmlTypes of Eruptions: PlinianPlinian eruptions are very explosive events that form enormous dark columns of tephra and gas that rise high into the stratosphere (>11 km). Such eruptions are named for Pliny the Younger, who carefully described the disastrous eruption of Vesuvius in 79 A.D. This eruption generated a huge column of tephrainto the sky, pyroclastic flows and surges, and extensive ash fall. This is a photograph of a plinian-type eruption of Mount Spurr, Alaska. This sent an eruption column to a height of about 18 km above sea level http://volcanoes.usgs.gov/Products/Pglossary/PlinianEruption.htmlWhat is tephra?Tephra is a general term for fragments of volcanic rock and lava regardless of size that are blasted into the air by explosions or carried upward by hot gases in eruption columns or lava fountains. Tephra includes large dense blocks and bombs, and small light rock debris such as scoria, pumice, and ash. http://volcanoes.usgs.gov/Products/Pglossary/tephra.htmlPyroclastic flowA pyroclastic flow is a ground-hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano as fast as 100 km/hour or more. The temperature within a pyroclastic flow may be greater than 500 C, sufficient to burn and carbonize wood. Once deposited, the ash, pumice, and rock fragments may deform (flatten) and weld together because of the intense heat and the weight of the overlying material. Pyroclastic flows are sometimes called Nue Ardentes, French for glowing avalanche and are associated with PlinianeruptionsPhoto at right is a pyroclastic flow sweeping down the side of Mayon Volcano, Philippines, 15 September 1984. Note the ground-hugging cloud of ash (lower left) that is billowing from the pyroclastic flow and the eruption column rising from the top of the volcano.Pyroclastic flows descend the flank of Mayon Volcano, Philippines. Maximum height of the eruption column was 15 km above sea level, and volcanic ash fell within about 50 km toward the west. There were no casualties from the 1984 eruption because more than 73,000 people evacuated the danger zones as recommended by scientists of the Philippine Institute of Volcanology and Seismology. http://volcanoes.usgs.gov/Imgs/Jpg/Mayon/32923351-020_caption.htmlColima (Mexico) Nue ArdenteAerial view of Colima Volcano showing an eruption of a pyroclastic flow. The nue reached a maximum distance of 4.5 km from the summit. Photograph courtesy of Abel Cortes, ColimaVolcano Observatory,University of Colima, November 22, 1998.Pelee May Chronology (contd.)May 8th, at around 3:00 am, mudflows destroy houses in Grand-Rivire, Macouba and Basse-Pointe. At 5:00 am, a mudflow floods Prcheur, carrying away 800 people. At 8:02 am, St. Pierre is destroyed by a nue ardente(glowing avalanche) devastating an area of approx. 22 sq miles.All members of the Volcano Commission were killedOnly 2 people who were actually inside the city survived the blast : Cyparis and Leon Compre. Many others who were on the boats anchored in the harbor, or in the neighborhoods around St. Pierre also got caught in the blast and killed. As a matter of fact, the only people who survived the blast (in its direct path), had a shelter inside a building, a jail cell, or in a boat, where the contact with the intense heat of the nuee ardente was limitedSt. Pierre before and after May 8, 1902http://www.mount-pelee.com/Ifacts.htm#HauntedCyparis the SurvivorCyparis said that the cell he occupied in the St. Pierre prison was an underground dungeon, which had no other window than a grated aperture in the upper part of the door. On the morning of May 8th, while he was waiting for breakfast, it suddenly grew very dark ; and almost immediately afterward hot air, mixed with fine ashes, came in through the door-grating and burned him. He rushed and jumped in agony about the cell and cried for help ; but there was no answer. He heard no noise, saw no fire, and smelled nothing except "what he thought was his own body, burning." The intense heat lasted only a moment, and during that time he breathed as little as possible. There was no smoke in the cell and the hot air came in through the door-grating without any noticeable rush or blast. He had on, at the time, hat, shirt, and trousers, but no shoes. His clothing did not take fire, and yet his back was very severely burned under his shirt.Cyparis got a contract to show his burns in the Barnum & Bailey American circushttp://www.mount-pelee.com/Ifacts.htm#HauntedThe Cell of Cyparis the Survivor http://www.mount-pelee.com/Ifacts.htm#HauntedWitness accounts of the May 8 eruptionOn the edges of the pyroclastic flow, the heat wasn't high enough and the blast wasn't strong enough to kill instantly or to cause heavy damage. The account of Mr Lassre and Mr Simonet, travelling from St. Pierre to Morne-Rouge on a mule-drawn carriage:"They saw it (the black cloud of the volcano) coming, just as they began the ascent of the Grande Reduit, and lashed their mules into a gallop with the hope of escaping it ; but the eastern edge of it caught them about sixty feet from the crucifix on the top of the hill. It approached with a roaring sound, struck them like a mighty wind, overturned and wrecked their carriage, setting the mules free, and then swept across the summit of the Grande Reduit, leaving them stunned, burned and half dead in the shattered vehicle. They saw no flame or fire, did not notice anything like suffocating gas, and smelled nothing except what they described as the "odor of smoke from lava." Both felt the intense heat of the blast as it swept over them, but Mr. Lassre did not realize that he was seriously burned until he crawled out of the wrecked carriage. Darkness became quickly afterward, but they succeeded in getting into a small deserted house near the shrine, and there they waited until it became light enough so that they could walk to Morne Rouge. Their clothing showed no signs of injury from heat, but their backs were badly burned or scalded. The skin peeled off their hands so that it hung from them in strips, and when they arrived at Morne Rouge, their shoes had to be cut from their burned and swollen feet."http://www.mount-pelee.com/Ifacts.htm#HauntedNue Ardente1902, MartiniquePelee chronology (continued)May 20th, a new paroxysm throws a dense ash plume over Fort-de-France.May 26th, and 28th, new violent eruptions are reported.June 6th, a new eruption sends a pyroclastic flow down the river Blanche valley and a large ash plume covers the island. Ashfalls are reported in St. Lucia.July 9th, a new nue ardente travels on the south-western side, and it is followed by several vertical explosions.August 30, a new avalanche partly destroys the villages of Morne-Rouge, and Ajoupa-Bouillon, reaching quarters in Basse-Pointe and Lorrain. The phenomenon claims another 1,000 lives. The area destroyed is approx. 44 sq miles.After August 30th, volcanic activity continues with the formation of lava spines at the summit. Other pyroclastic flows erupt, mainly down the river Blanche valley.The activity stopped in 1905.St. Pierre todayShortly after the eruption, St. Pierre was completely abandoned. But slowly families were drawn to the ruins by the cheap price of land, and the desire to rebuild the city. The first building to be constructed among the ruins was a hotel, mostly thanks to tourism which developed after the disaster. St. Pierre currently has about 6,000 inhabitants.Deadliest eruptions in Latin AmericaVolcano Country Year DeathsNevado del Ruiz Colombia 1845 1,000Cotopaxi Ecuador 1877 >300Soufrire St. Vincent (L. Ant.) 1902 1,680Mount Pele Martinique (L. Ant.) 1902 29,000Santa Maria Guatemala 1902 ~1,500El Chichn Mexico 1982 >2,000Nevado del Ruiz Colombia 1985 25,000http://volcanoes.usgs.gov/Hazards/Effects/Fatalities.htmlNevado del Ruiz, ColombiaLocated in the Andes mountains of South America, Nevado del Ruiz is the northernmost and highest Colombian volcano with historical activity. With a summit elevation of 5,389 m, the volcano is the second highest active volcano in the western hemisphere.Its summit is covered with 25 km2 of snow and ice even though it's located only 500 km from the equator. Beginning in November 1984, the volcano began showing signs of unrest, including earthquakes, increased fumarolic activity from the summit crater, and small explosions.http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.htmlNevado del RuizAndes N. Volcanic ZoneAndes Central Volcanic ZoneAndes S. Volcanic ZoneLesserAntillesIsland ArcCentralAmericaTrans-Mexico Volcanic BeltNevado del Ruiz, Colombiaat the northern end of the Andes Northern Volcanic ZoneColombia1,138,910 sq km41,000,000 peoplePer capita GDP $6300Colombia Geography3 mountain ranges in west: Cordillera Occidental, Central, and OrientalEastern lowlands are part of the Amazon and Orinoco drainage basinsWhat is a lahar?Lahar is an Indonesian word for a rapidly flowing mixture of rock debris and water that originates on the slopes of a volcano. Lahars are also referred to as volcanic mudflows or debris flows. They form in a variety of ways, chiefly by the rapid melting of snow and ice by lavas, intense rainfall on loose volcanic rock deposits, and breakout of a lake dammed by volcanic deposits. Volcanoes covered with ice and snow are especially dangerous because a small eruption can melt a tremendous amount of ice and produce great laharsA small lahar triggered by rainfall rushes down theNima II River near the town of El Palmar in Guatemala. The lahar developed on the slopes of Santiaguito volcano. http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.htmlEvents prior to Nov. 13, 1985Nevado del Ruiz experienced many minor earthquakes and steam eruptions for 51 weeks prior to the November 13 eruption. The activity was just enough to keep people nervous, particularly because lahars had killed 1000 people in1845. Since Columbia had no equipment to monitor the volcano, or geologists skilled in using such equipment, expertise could only come from other countries. A scientific commission and some journalists visited the crater in late February. By July, seismographs were obtained from several countries to monitor earthquakes which would help plot the movement of rising magma beneath the volcano. Money was obtained from the United Nations to help map the areas that were thought to be at the greatest risk. The resulting report and volcanic hazards map were finished on October 7, but only ten copies were distributed. Based on the report, the National Bureau of Geology and Mines (INGEOMINAS) declared that a moderate eruption would produce " . . . a 100 percent probability of mudflows . . . with great danger for Armero . . . Ambalema, and the lower part of the River Chinchina." However, some government officials dismissed the report as "too alarming" and authorities did not want to evacuate people until they were assured of the necessity. Continuous earth tremors began beneath the volcano on November 10. This prompted a group of scientists to visit the crater on November 12. However, they saw nothing to suggest imminent danger and they did not recommend an evacuation. http://www.geology.sdsu.edu/how_volcanoes_work/Nevado.htmlThe Eruption of Nov. 13, 1985Broad summit of Nevado del Ruiz. An explosive eruption from Ruiz's summit crater on November 13, 1985, at 9:08 p.m. generated an eruption column and sent a series of pyroclastic flows and surges across the volcano's broad ice-covered summit. Within minutes, pumice and ash began to fall to the northeast along with heavy rain that had started earlier in the day. The crater was enlarged slightly by the eruption, and the summit area was quickly covered with layers of pyroclastic flow deposits as thick as 8 m. This eruption was preceded by a strong phreatic (steam) explosion from the crater at 3:05 p.m. In this view, the dark pyroclastic-flow deposits are partly covered with fresh snow.Nov. 13 Eruption & LaharsThe volcano exploded violently on November 13, 1985. The initial blast began at 3:06 p.m., and two hours later pumice fragments and ash fell on Armero. However, the citizens of Armero were placated by reassuring radio messages from the mayor and from a local priest over the church public address system. Nevertheless, the Red Cross ordered an evacuation of the town at 7:00 p.m. However, shortly after the evacuation order the ash stopped falling and the evacuation was called off.At 9:08 p.m., hot tephra began to erupt from the summit crater and quickly began to meltthe summit ice cap. Unfortunately, a storm obscured the summit area. Meltwater mixed with the erupting pyroclastic fragments to generate a series of hot lahars. One lahar flowed west down the River Cauca, submerging the village Chinchina and killing 1,927 people. Other lahars followed the paths of the 1595 and 1845 mudflows. Traveling at 50 kilometers per hour, the largest of these burst through an upstream dam on the River Lagunillas and reached Armero two hours after the eruption began. Most of the town was swept away or buried in only a few short minutes, killing three quarters of the townspeople.Generation of the Nevado del Ruiz laharHeadwaters of Azufrado River. Hot rock fragments of the pyroclastic flows and surges quickly eroded and mixed with Ruiz's snow and ice, melting about ten percent of the volcano's ice cover. In places, channels 100 m wide and 2-4 m deep were eroded into the icecap. Flowing mixtures of water, ice, pumice and other rock debris then poured from the summit and sides of the volcano into rivers draining the volcano. In one river, scientists found a piece of ice 2 m across about 3 km from the crater. This view of Ruiz is from the northeast.http://volcanoes.usgs.gov/Imgs/Jpg/Ruiz/30410135_062_large.jpgGeneration of the Nevado del Ruiz laharHeadwaters of Gual River.Pumice and meltwater produced by the hot pyroclastic flows and surges swept into gullies and channels on the slopes of Ruiz as a series of small lahars. After descending several thousand meters and eroding loose rock debris from the sides of the volcano, the lahars were funneled into all six major river valleys leading from Ruiz. Here in the headwaters of the GualRiver on the north side of Ruiz, a lahar took several paths on its journey downstream.Gual River valley. Flowing downstream from Ruiz at an average speed of 60 km per hour, lahars eroded soil, loose rock debris and stripped vegetation from river channels. By incorporating water and debris from along river channels, the lahars grew in size as they moved away from the volcano--some lahars increased up to 4 times their initial volumes. In some of the narrow canyons downstream from the volcano, as shown here in the GualRiver, lahars were as thick as 50 m!http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.htmlGual River. Houses and towns located high enough above river channels escaped damage from the lahars. In the Gual River valley, at least two lahar pulses were reported by eyewitnesses, separated by 5 to 15 minutes depending on distance from the volcano. Eyewitnesses reported that the noise created by the passage of each pulse made their houses and the ground shake and that conversation, even by shouting, was impossible.http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.htmlFormer site of ArmeroThree quarters of Armeros 28,700 inhabitants perished.Accounts from survivors indicate Armero was inundated with several pulses of flowing material. The first arrived at 11:25 p.m. and consisted of a flood of cold water that overflowed the Ro Lagunillas channel, sweeping into downtown Armero. Only a few centimeters deep in town, this water was from a lake located just upstream that had been displaced when lahars entered the lake.The second pulse arrived at 11:35 p.m. This was the largest pulse and within 10 to 20 minutes, destroyed most of the buildings and swept away most of the people in Armero. Flow depths of the lahar ranged from 2 to 5 m.The third pulse arrived at 11:50 p.m. with a velocity of about half of the second one. Then, in the next hour or so, a series of smaller pulses (6 to 8) was experienced by survivors trapped in the mud. These pulses lifted people floating in the mud and pushed them a few meters ahead.One last pulse struck Armero a short time after 1 a.m. on November 14. Lessons from Nevado del RuizFor the generation of lahars on ice- and snow-covered volcanoes, the deadly 1985 eruption of Nevado del Ruiz offers several key lessons for scientists, emergency-response professionals, and communities located downstream of such volcanoes: 1) catastrophic lahars can be generated on ice- and snow-capped volcanoes by relatively small eruptions 2) the surface area of snow on an ice cap can be more critical than total ice volume when considering lahar potential 3) placement of hot rock debris on snow is insufficient to generate lahars -- the two materials must be mechanically mixed together for rapid heat transfer 4) lahars can increase their volumes significantly by entrainment of water and eroded sediment 5) valley-confined lahars can maintain relatively high velocities and can have catastrophic impacts as far as 100 km downstream http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.htmlMt. Rainier, Washington: Sleepless in SeattleMount Rainier volcano (4,393 m) is potentially the most dangerous of the active volcanoes of the Cascade Range in the Pacific Northwest. The volcano towers more than 3 km above several river valleys that lead to populated regions, and it has a cover of snow and ice that is equal in volume to that at all the other Cascade Range volcanoes combined. The volcano's most recent landslide-triggered lahar happened about 500 years ago and swept more than 50 km down the Puyallup River valley to the Puget Sound lowland. The lahar buried the valley near the town of Orting with deposits 3 to 5 m thick.http://volcanoes.usgs.gov/About/Highlights/RainierPilot/30410142-011_caption.html


View more >