Volcano News & Questions from Students VOLCANIC ERUPTIONS Physical Phenomena Causes – movement at plate boundaries Geography – spatial distribution Forms and eruption styles Magnitude Prediction – looking back & monitoring Hazards – quakes, blasts; release of ash, gas & lava Impacts Fatalities Economic Mitigation & Preparedness Begins with understanding vulnerability Recently, eruption of Icelandic volcano halted air travel Breaking Volcano News http://www.volcanolive.com/news.html …and news of breaking volcanoes History shows that when Eyjafjallajökull erupts, it’s larger neighbour Katla is generally not far behind. Katla is overdue. Katla’s eruption may be 10 or more x the size of the Eyjafjallajökull eruption –significant floods of fresh glacial-melt water into the sea (flow equal to Amazon + Mississippi + Nile + Yangtze occurred following 1755 eruption), a column of ash rising Chaiten, Chile 20km, or more, into the jet stream and spread over N Hemisphere. The Laki eruption in Iceland in 1783 resulted in famine across W Met Office, summer 2010 Europe, and as far S as Egypt, one of the longest and coldest ..as ash entrained in the atmosphere moved from winters on record in N America, and the death of 10,000s of Iceland across the Atlantic. people from gas poisoning and famine. 1 Merapi is at a subduction zone, where the Indo-Australian Plate is sliding NEWS beneath the Eurasian Plate and part of the Pacific Ring of Fire Stratigraphic analysis reveals that eruptions in the Merapi area began about Merapi Eruption 400,000 years ago, and from then until about 10,000 years ago, eruptions were effusive, and outflowing lava emitted was basaltic. More recent than 10,000 y ago, eruptions have become more explosive, with viscous andesitic lava generating lava domes. Dome and column collapse Have generated large explosions and pyroclastic flows. Typically, small eruptions now occur every 2-3 y, larger ones every 10-15 y. Notable eruptions, often causing many deaths, have occurred in 1006, 1786, 1822, 1872, and 1930—when 13 villages were destroyed and 1400 people killed by pyroclastic flows. A very large eruption in 1006 is claimed to have covered all of central Java with ash. Old News • >1300 volcanoes known to have erupted in Holocene epoch (last 10 000 years) • ~500 classified as ‘active’ (i.e. http://video.google.com/videoplay?docid=39774163 known to have erupted in 82972126736#docid=-3680513146102540221 recorded history) • Remainder classified as ‘dormant’ (may become active again) or ‘extinct’ (not expected to erupt again), but Vesuvius was thought Plus new vents: e.g. to be extinct before AD 79! Paricutin (Michoacan, Mexico) shown erupting in 1943 (graphic by Diego Rivera) Tectonic plate boundaries subducting – spreading - sliding Physical Phenomena Causes – movement at plate boundaries Geography – spatial distribution Forms and eruption styles 2 Spreading centers Oc-Cont: Subduction- W coast of Americas Cont-Cont: Convergence- Himalayan Mt. Rifting (or Spreading)- E African Rift Valley Oc-Oc: Subduction- Aleutian Islands Spreading- Mid-ocean ridges Distribution of active volcanoes Volcanoes Eruptive style and hazard depends on: •Tectonic setting •Depth of magma formation •Rate of magma movement to the surface •Percent and type of volatiles (gases) 60% around Pacific; 20% in Mediterranean region Volcanoes - tectonic settings Oceanic ridge, Subduction Hotspots zones examples? Basic/Mafic volcanics Acidic/Felsic volcanics •Low SiO2 •High SiO2 •Fluid lava (10 m/s) •Viscous lava (3 m/s) •Low gas pressure > •High gas pressure > little explosive activity explosive activity 3 As magma cools, crystals form & viscosity, & gas & steam content increase Classification of volcanic eruptions 1) Ultramafic- Kaolinic, Very high Temp, Very low Si content (after Scheidegger) (<45%) , Fluid, River of molten rock, Gas bubbles escape gently, Rare because earth’s core has cooled over time Low Risk High Risk Gas Pressure 2) Mafic- Basaltic, High Temp, Low Si content, Int viscosity Low profile shield domes Low 3) Intermediate- Andesitic, Moderate temp, Moderate Si content, Relatively high viscosity, Steep composite volcanoes High Lava Type Lava 3) Felsic- Rhyolitic, Medium Temp, High Si content (>65%), Viscous, Gases trapped leading to violent explosions of ash & pyroclastic flows, Lava domes Oceanic ridge, Subduction Hotspots zone SHIELD -Non explosive -Ocean setting Basaltic lava flows STRATO/STEEP COMP -Explosive -Convergent plate boundaries FISSURE -Low power -Fissures & faults “Aa” (blocky lava) flow, Hawai “Pahoehoe” (ropy lava) flow, Reunion CINDER CONE/ LAVA DOMES Hazards - property burnt and buried by lava -Accumulation around vent -Highly explosive Explosive eruptions occur when gases are trapped and magma becomes bouyant.. Recent major lava flows, Hawai’i 4 Pyroclastic flows, a ground-hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that is more dense than atm and therefore rushes down volcano flanks VEI Volume of tephra Eruption (m3)type “Super-volcanoes” 0 nonexplosive Icelandic/ Eruption Hawaiian magnitude 1<105 6 = 2~10 Strombolian 3~107 Vulcanian Volcanic 4~108 Vesuvian Explosivity 5~109 Plinian 10 Index 6~10 Peléan 7~1011 8~1012 “supereruption” Identification of high-risk volcanoes PREDICTING OCCURRENCE & IMPACTS OF VOLCANIC ERUPTIONS • Frequency and nature of past eruptions • Distribution and nature of eruptive products • Population density and property value in vicinity of volcano RISK = HAZARD X VULNERABILITY 5 Vesuvius and region Campi Flegrei La Solfatara MISENUM Identifying tephra layers in ancient lake sediments help determine occurrence of eruptions and establish hypothetical recurrence intervals Why wasn’t Vesuvius recognized as high-risk by the Romans? Mount Vesuvius: Eruptive style- 2 main Bed Date (BP) Volume (km3) recent major eruptions types Pompeii ~1900 Plinian 2.8 • A.D. 79: destruction of Pompeii and AP6 ~2200 Strombolian ? Strombolian to AP5 ? 0.08 Herculaneum; Vulcanian AP4 ? Phreato-Plinian 0.12 Strombolian to AP3 ~2700 0.15 • 80 eruptions since then - Vulcanian Sub-Plinian to phreato- most violently in 1631 and 1906; AP2 ~3000 0.14 Plinian quiet since 1944 Sub-Plinian to phreato- AP1 ~3300 0.15 Plinian Avellino ~3450 Plinian 1.5 From data in: Andronico, D. and Cioni, R. 2002. Bull. Volcanology 64, 372-391. • Can we predict when a volcano will erupt? Identification of high-risk volcanoes (1984) • clues from past eruptions & remnant pyroclastic flows • monitoring for warning signs such gas emission & small SE Asia and Pacific = 42 Total = 89 EQ Americas and Caribbean = 40 of ~500 active Africa and Europe - 7 volcanoes) • The problem of prediction Despite prediction of likelihood, it is difficult to pinpoint exactly when an eruption may occur. Omissions can be significant, e.g. Nevado del • Often, moving magma doesn't result in an eruption, but Ruiz ~25000 killed in1985 instead cools below the surface. Caveat: “low ratings may simply reflect • Monitoring is expensive. incomplete or incorrect information, not • Many volcanoes erupt only every few hundred or thousand necessarily low risk. In fact, volcanoes not years. listed should be the focus of... investigation” • Nevertheless, volcanic eruptions don't occur without [Yokohama et al. (1984)] warning and monitoring devices can allow time for evacuation as in the case of Merapi 6 Monitoring techniques Tools to detect warning signs: seismographs detect Gas sampling at vents small earthquakes, tiltmeters and geodimeters measure subtle swelling, correlation spectrometers (craters, fumaroles) measure amounts of sulfur dioxide. Tectonic deformation, Campi Flegrei, Italy (1982-1985 pulse) City of Naples Monitoring and prediction at Mt St Helens, 1982 La Solfatara, one of several small active craters in the Campi Flegrei 7 Predicting Impacts of Katla Eruption Air travel – the recent 6-day chaos would potentially be dwarfed by one that could last months. This would not only impact passengers, but freight, too. Tourism would certainly be impacted negatively, but so would food imports and general freight movement. Agriculture – the impact of a prolonged cold spell would drastically affect crop production in Europe and, potentially, elsewhere in the Northern Hemisphere. For Europe, this would Recent uplift in Iceland in vicinity of just add to the difficulties faced by the lack of air transport to bring underice volcanoes suggest a large in fresh produce from elsewhere. eruption may be imminent with Power – of course, a lengthy period of exceptionally cold weather potentially catastrophic would push up power consumption dramatically. prolonged cold consequences as a result of takes its toll. Where would this wealth go, and who would benefit? Caldera collapse. Mt. Vesuvius Types of modern volcanic Herculaneum hazards excavated area of Roman http://www.yo Herculaneum utube.com/wa (20 m below tch?v=uphPM modern city) FFC5GI&feat ure=related http://volcanoes.usgs.gov/Hazards/What/hazards.html VOLCANIC HAZARDS •Earthquake Volcanic hazards: • deaths (AD 1900-2000) •Directed Blast •Tephra deposition •Gas Release •Lava Flow •Debris Avalanche, Landslide, and Tsunami •Pyroclastic Surge • •Pyroclastic Flow • •Lahars 8 Ash cloud from the eruption of Mt. Volcanic Spurr (Alaska) in 1992 ash Yakima, WA (May, 1980) Fine-grained volcanic ash can cause health problems in susceptible people, clog ventilation systems, cause electrical short circuits, damage crops, and wreck jet engines (e.g. the BA 747 that lost all 4 engines and dropped 4 km after encountering an ash