Mount St. Helens 1980 EruptionSmall earthquakesSmall steam and ash eruptions in March and April 1980USGS monitoring station set up north of the mountain on Coldwater RidgeMay 1980 - North side of mountain began to bulge, many micro-earthquakes, eruption was imminent; “red-zone” closed“Vancouver! Vancouver! This is it . . .” David Johnston8:32 AM 5/18/80 a magnitude 5.1 earthquake triggered the Big Eruption!The unstable bulge on the North side collapsed and exposed magma in a shallow chamber to airGas bubbles formed instantaneously in the magma causing expansion, a shock wave and a big ash eruptionMost of the force of the eruption was directed horizontally to the NorthEruption viewed from Mount AdamsGary Rosenquist photos made reconstruction of the eruption sequence possibleRosenquist 4 and 5Rosenquist 6 & 8Rosenquist 10Reconstructed Eruption Sequence (see handout)After the first few minutes, the ash erupted upward and drifted ENE with the prevailing windsView from the South on May 19Effects of May 18, 1980 eruptionSummit collapsed to form debris flows to the north and westDebris flow deposits to NorthToutle River Mud FlowDirected blast vaporized vegetation near the volcano, stripped and flattened trees further outDirection of trees indicates blast dynamicsAshflowsAshflow on SnowDome growth over next few years: Will it fill the crater?Photos of MSH Before and After May 18, 1980We think Mount St. Helens 1980 was a big deal, not by comparisonMt. St. Helen’s 1998Recovery - 20th Anniversary National Geographic issueJohnston Ridge ObservatoryNew Dome-building eruptions began in Oct. 2004, dome continues to growFun at Spirit Lake in the 1940sVolcanic HazardsDirected blastHot ash flows, lava flowsAirfall ash (threatens airplane visibility and engines)Mudflows = laharsMixture of melted ice, debris, water, and ashThreaten people, cities and towns far awayLahars from Mt. Rainier could threaten Seattle and/or TacomaLahars=Mudflows are the main Volcanic Hazards at Mt. RainierUSGS - Volcano Disaster Assistance Program (VDAP)http://volcanoes.usgs.gov/About/Where/VDAP/main.htmlEstablished after volcanic disaster in Columbia (Armero) in 1985VDAP is a mobile, well equipped team of experienced volcanologists who can respond whenever a volcano crisis threatens anywhere in the worldSuccessful prediction of 1991 eruption by VDAP at Pinatubo may have saved thousands of livesRecent EruptionsNevado del Ruiz, ColumbiaNov. 13, 1985 eruptionArmero mudflow >23,000 killedPinatubo, PhilipinesErupted June 15, 1991threatened 1,000,000 people, only a few hundred perishedThere’s a Great Book about Volcanologists who study explosive Volcanoesin the post-St. Helens eraVolcano Cowboysby Dick Thompson, 2000Geol 285 - Petrology, Dr. Helen M. Lang, West Virginia University, Fall 2005Mount St. Helens 1980 Eruption• Small earthquakes• Small steam and ash eruptions in March and April 1980• USGS monitoring station set up north of the mountain on Coldwater Ridge• May 1980 - North side of mountain began to bulge, many micro-earthquakes, eruption was imminent;“red-zone” closed“Vancouver! Vancouver! This is it . . .” David Johnston8:32 AM 5/18/80 a magnitude 5.1 earthquake triggered the Big Eruption!• The unstable bulge on the North side collapsed and exposed magma in a shallow chamber to air• Gas bubbles formed instantaneously in the magma causing expansion, a shock wave and a big asheruption• Most of the force of the eruption was directed horizontally to the NorthEruption viewed from Mount AdamsGary Rosenquist photos made reconstruction of the eruption sequence possibleRosenquist 4 and 5Rosenquist 6 & 8Rosenquist 10Reconstructed Eruption Sequence (see handout)After the first few minutes, the ash erupted upward and drifted ENE with the prevailing windsView from the South on May 19Effects of May 18, 1980 eruptionSummit collapsed to form debris flows to the north and westDebris flow deposits to NorthToutle River Mud FlowDirected blast vaporized vegetation near the volcano, stripped and flattened trees further outDirection of trees indicates blast dynamicsAshflowsAshflow on SnowDome growth over next few years: Will it fill the crater?Photos of MSH Before and After May 18, 1980We think Mount St. Helens 1980 was a big deal, not by comparisonMt. Pinatubo, Philipines, 1991 5 cubic kmMt. St. Helens, 1980 1 cubic kmMt. Katmai, AK, 1912 12 cubic kmKrakatoa, Indonesia, 1883 18 cubic kmTambora, Indonesia, 1815 80 cubic km 1816-“the year without a Summer”Vesuvius, AD 79 3 cubic kmMt. Mazama, 4600 BC 42 cubic km (Crater Lake)Mt. St. Helen’s 1998Recovery - 20th Anniversary National Geographic issueJohnston Ridge ObservatoryNew Dome-building eruptions began in Oct. 2004, dome continues to growSee Sugar Bowl Dome Camera: http://vulcan.wr.usgs.gov/Volcanoes/MSH/Eruption04/Monitoring/sugarbowl_remote_camera_10-04_to_09-05.html Fun at Spirit Lake in the 1940sVolcanic Hazards• Directed blast• Hot ash flows, lava flows• Airfall ash (threatens airplane visibility and engines)• Mudflows = lahars– Mixture of melted ice, debris, water, and ash– Threaten people, cities and towns far away– Lahars from Mt. Rainier could threaten Seattle and/or TacomaLahars=Mudflows are the main Volcanic Hazards at Mt. RainierUSGS - Volcano Disaster Assistance Program (VDAP)• http://volcanoes.usgs.gov/About/Where/VDAP/main.html • Established after volcanic disaster in Columbia (Armero) in 1985• VDAP is a mobile, well equipped team of experienced volcanologists who can respond whenever avolcano crisis threatens anywhere in the world• Successful prediction of 1991 eruption by VDAP at Pinatubo may have saved thousands of livesRecent Eruptions• Nevado del Ruiz, Columbia – Nov. 13, 1985 eruption– Armero mudflow >23,000 killed• Pinatubo, Philipines– Erupted June 15, 1991– threatened 1,000,000 people, only a few hundred perished There’s a Great Book about Volcanologists who study explosive Volcanoes in the post-St. Helens era• Volcano Cowboys• by Dick Thompson,