Explosion of Mt. St. Helens

Heigth of eruption column (km) Explosion of Mt. St. Helens First activity on the 18. 5. 1980, 08:32h On On the the22. 7. 7. 1980 ash clouds rich 18 18 km height within 8 minutes! Subduction-related volcanoes along the west coast of N America Decker, R. & Decker, B., 1985 1

Mt. St. Helens before the eruption Decker, R. & Decker, B., 1985 (Spektrum) Decker, R. & Decker, B., 1985 (Spektrum) Eruption of Mt. St. Helens 2

After the eruption of Mt. St. Helens Decker, R. & Decker, B., 1985 (Spektrum) Topographic model Mt. St. Helens Decker, R. & Decker, B., 1985 (Spektrum) Upper most 400m were missing 3

Mt. St. Helens Lava- and mud flows Decker, R. & Decker, B., 1995 Damage around Mt. St. Helens Burned forests Pyroclastites Ash Mud flows Decker, R. & Decker, B., 1985 Derooted trees 4

Heigth of eruption cloud Surtseyan Phreato-plinian Volcanian Phreato - magmatic eruptions c Explosivity Classification scheme for explosive eruptions, according to the area covered by pyroclastic deposits (D = tuff cover) and the degree of tephra fragmentation (F). Next to purely magmatic eruptions, at the interplay with external water, mild phreato magmatic (volcanian) and extreme, violent phreato magmatic (surtseyan and phreatoplinian) eruptions can be distinguished. D=Area, covered by the 1%-Tmax-isopach (Tmax=maximal thickness of the deposit); F = Weight % of <1 mm grain size in the sample at 10% -Tmax-isopach. 1 gentle 100-1000 m 10,000s m 3 Haw/Strombolian daily Stromboli 2 explosive 1-5 km 1,000,000s m 3 Strom/Vulcanian weekly Galeras, 1992 3 severe 3-15 km 10,000,000s m 3 Vulcanian yearly Ruiz, 1985 4 cataclysmic 10-25 km 100,000,000s m 3 Vulc/Plinian 10's of years Galunggung, 1982 5 paroxysmal >25 km 1 km 3 Plinian 100's of years St. Helens, 1981 6 colossal >25 km 10s km 3 Plin/Ultra-Plinian 100's of years Krakatau, 1883 7 8 VEI Description Plume Height Volume Classification How often Example nonexplosive 0 < 100 m 1000s m 3 Hawaiian daily Kilauea supercolossal megacolossal >25 km 100s km 3 Ultra-Plinian 1000's of years Tambora, 1815 >25 km 1,000s km 3 Ultra-Plinian 10,000's of years Yellowstone, 2 Ma Explosivity index [VEI] E = percentual content of pyroclastics VEI - Volcanic Explosivity Index VEI 0 33% Explosive: VEI 67 100% 5

Calderas Caldera (Spanish (span.) Der for Kessel kettle or pot) collapsed volcano Name Leopold von Leopold Buch (1825) von Taburiente Buch caldera, (1825) La Palma Explosion- Explosions-Caldera Collaps- Einsturz-Caldera Erosion- Erosions-Caldera Caldera (Spanish for kettle) collapsed volcano Leopold von Buch (1825) Taburiente, La Palma Caldera, formed subsequently to large eruptions by collapsing above the partly emptied magma chamber. Origin: Hawaiian to plinian eruptions. Plinian calderas produce ignimbrites*. Calderas can attain several 10s of km in diameter and be circular to ellipsoidal, and bound by faults forming a polygonal pattern. Resurgent Caldera: through new magma intrusion rising and updoming caldera. *Ignimbrite: deposits of a pumice rich pyroclastic flow. 6

Origin of a Caldera Collaps- Caldera Magma chamber Degassing Pyroclastic flows Resurgent Caldera Ignimbrite cover New magma rises Friedrich, W.L. et al., 1985 New eruption Hot springs and geysirs Ring complexes / Couldron Subsidence Caldera-Collaps, Ring-Dikes, Cone-Sheets 7

Crater Lake, Oregon 8

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Caldera Taburiente La Palma (Canary islands) Distribution of ash Explosion of of the the Toba caldera 75 75000 years ago Francis, P., 1985 11

Explosion of of the the Toba caldera 75 75000 years ago Calderas in North America Canada United States 1 Mill.y. Valles-C. (New Mexico) 700 000 y. y. Long-Valley- Caldera (California) Aus Francis, P., 1985 (Spektrum) 600 000 y. y. Yellowstone-Caldera (Wyoming) 12

Krakatau-Explosion 1883 Before the the explosion Francis, P. & Self, S., 1985 Krakatau 1883 After explosion Francis, P. & Self, S., 1985 13

New volcano of the Krakatau-Caldera 1927 Francis, P. & Self, S., 1985 Santorini-Caldera - Atlantis? Friedrich et al., 1985 Destroyed Minoian (ancient Greek) cultural centres, in in red 14

Pumice on Thera, Santorini Tuff on Thera, Santorini 15

Gas volcanoes (Maars), Maar, subaerial volcano form of a shallow crater, often forming a lake. Formed through phreato-magmatic explosions of mostly basaltic magmas, in contact to large amounts of ground water. Maars are monogenetic volcanoes, active only for few days or weeks. Because of the violent explosions of extending gas and water vapour, the country rocks become strongly fragmented down to several hundred metres depth, and ejected violently. Simultaneously, country rocks tend to slump into the active maar volcano (collapsing of walls). After the eruption a lake is formed, dammed by a flat tuff ring around the maar crater. Below the maar, volcanic breccias fill the explosion vent down to several hundred metres depth (Diatrem) Maar genesis valley Tal Tal Grundwasser water Ground Grundwasser Bruchzone Bruchzone Fault valley Tal Tal Grundwasser water Ground Grundwasser Contact Kontaktzone zone Kontaktzone aufsteigendegendes basaltic aufstei- Rising Basaltmagma Basaltmagma magma Lapilli Erup- Erupti tions- ve kam- mer cham mer ber Lorenz, V., 1985 16

Gas volcanoes (Maares), Eifel, Germany Lorenz, V. 1985 Weinfelder Maar, Germany Lorenz, V. 1985 17

Laacher lake (Maar in the Eifel) Tephra thickness in cm Tuff of the Laacher Lake-Volcano, with pumice enclosing a blue hauyne crystal (foid) 11 11000 years ago Ash transported to to Scandinavia Post-volcanic phenomena Gas Exhalations: Basaltic: CO 2, CO, H 2, CH 4, H 2 S Andesitic: H 2 O, HCl, HF 18

Post-volcanic phenomena: The terminal degassing of magma, after the volcanic activity has largely ceased, causes natural phenomena such as : Fumaroles (Gas and H 2 O, mainly phreatic and not juvenile) Solfatares (H 2 S) Mofettes (CO 2 ) = CO 2 -rich springs Geysires = thermal, heated groundwater expulsions Geysir, Iceland Fumaroles: Solfatares: Fumarole: Merapi volcano, Indonesia Post-volcanic phenomena Gas, vapour H 2 S Fumaroles: Icleand Mofettes: CO 2 19

Solfatares with sulphur mineralization, Haymey and Askja, Iceland Mud mofette (CO 2 ), Iceland 20

Geysir, Iceland Magma-meteoric water interaction Hot spring Descending, cold rain water Geysir Ascending hot water Fault zone Magma Press & Siever, 1991 21

Interactions of Volcanoes with other Geosystems Reaching the surface, magma (lava) degasses to the atmosphere and hydrosphere. Water dissolves volcanic rocks and changes its chemistry and eventually, the chemistry of the ocean. Volcanism and the hydrosphere: fumaroles and geysers Volcanism and the atmosphere Volcanic eruptions are rich in gases and in ash that can have influence on climate: aerosols and ash Tephra on the slopes of Pintubo (0,2km 3 ) Erupted pyroclastic material (9,0km 3 ) Pyroclastic flows in western areas Pyroclastic flows in eastern areas (2,0km 3 ) Pyroclastic sediments in the rivers Silt and mud transported to the coast (0,2km 3 ) Pyroclastic flows in western areas Long -term deposited pyroclastic material (3,9km 3 ) Erosion of older deposits (0,2km 3 ) Lahar deposits (2,3km 3 ) Volume and distribution of different tephra layers after the explosion of Mt. Pinatubo 1991 22

Influence of volcanism on climate Stratosphere Solar radiation Increased albedo Heterogenous chemistry Equal density zone (umbrella) Ash, H2O; HCl warming Aerosol layer Convective eruption column Ash, H2O; HCl Troposphere Gas acceleration Infra red Cooling down of the Earth surface, volcanic winter Acid content in Greenland ice Influence of volcanism on climate Duration of the Laki eruption, Iceland Winter temperature (December-February) 23

Positive and negative climate forcing FCCH=Fluorine- Chlorine-Carbo- Hydrates Ozone (O 3 ) killers Greenhouse gases NO 2 FCCH Positive climate forcing (left column) through anthropogenic greenhouse gases Ozon lost S smoke Tropospheric aerosols Sun radiation clouds Negative climate forcing (left column) through stratospheric aerosols from the Mt. Pinatubo eruption Volcanism and Human Affairs Natural resources volcanic soils industrial materials ore formation heat energy 24

Volcanism and Human Affairs: Geothermal Energy non-explosive highly explosive Number of eruptions in each explosivity group in % Years between eruptions VEI Death toll % c. 550 active volcanoes worldwide c. 60 eruptions per year Since 1700: >350 000 mortalities 1900-1986 Total of 76 000 Yearly average of 880 deaths Pyroclastic flows Lahars other Hunger Tsunamis The tsunami of December, 2004 in Indonesia caused c. 260000 fatalities. The earth quake 2009 in Port au Prince, c. 250000 deaths, changing the statistics drastically. Japan 2011? 25

Volcanism and Human Affairs But one earth quake in Los Angeles or a single eruption of e.g. Fujiyama, close to Tokyo, can again change the statistics! AD BC BC BC BC Erupted magma volume in km 3 26

Volcanism and Human Affairs: Potentially Hazardous Volcanoes 27

Thought questions for this chapter Why are eruptions of stratovolcanoes generally more explosive than those of shield volcanoes? What might be the effects on civilization of a Yellowstone-type type caldera eruption? How do interactions between volcanic geosystems and the climate system increase volcanic hazards? 28