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PH307 Disasters: Volcanos Dr. Dirk Froebrich This presentation can be found at:

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Presentation on theme: "PH307 Disasters: Volcanos Dr. Dirk Froebrich This presentation can be found at:"— Presentation transcript:

1 PH307 Disasters: Volcanos Dr. Dirk Froebrich This presentation can be found at:

2 Volcanos

3 Kílauea, Hawai‘i

4 Mauna Kea, Hawai‘i... The summit appears utterly lifeless except for a few unlucky bugs blown up from below and a few flightless native insects that feed on them. No trees, no plants. Just lifeless void. The mountain last erupted 4500years ago and is considered dormant. (If it erupts when you are up there, please disregard this last statement.) 4205m

5 Outline causes of volcanism types of volcanos types of eruptions methods of predicting eruptions dangers, effects and how to minimise damage/loss of life  Seminar

6 Causes of Volcanism

7 Active Volcanos (~1900)

8 Earthquake Epicenters since 1963

9 Plate Tectonics

10

11 Types of Volcanos

12 Volcano Types (by position) mid ocean ridges usually at sea floor, but e.g. Iceland subduction zones e.g. Mt. Etna, the Ring of Fire Hotspots/Plumes e.g. Hawai‘i, Eifel, Auvergne

13 Volcanos in Subduction zones

14 Mount Etna

15 Hotspot Volcanos

16

17 Volcano Types (by shape) Shield Volcanos - huge quantities of basaltic lava gradually build up wide shield like mountain - hot fluid lava flows - e.g. Hawai‘i

18 Shield Volcanos Olympus Mons (Mars)Mauna Loa SkjaldbreidurMt. Edziza

19 Volcano Types (by shape) Shield Volcanos - huge quantities of basaltic lava gradually build up wide shield like mountain - hot fluid lava flows - e.g. Hawai‘i Strato Volcanos - strata – internally consistent layer of rock - tall conical mountain build up by a sequence of lava flows and ejecta - e.g. Mt. Fuji, Vesuvius, Stromboli, Popocatépetl, Mt. St. Helens

20 Strato Volcanos Mt. St. HelensPopocatépetl Mt. FujiStromboli

21 Volcano Types (by shape) Shield Volcanos - huge quantities of basaltic lava gradually build up wide shield like mountain - hot fluid lava flows - e.g. Hawai‘i Strato Volcanos - strata – internally consistent layer of rock - tall conical mountain build up by a sequence of lava flows and ejecta - e.g. Mt. Fuji, Vesuvius, Stromboli, Popocatépetl, Mt. St. Helens Cinder Cones - small (30-400m high), build up around vents - can be on flanks of other volcanos or isolated Submarine & Subglacial Volcanos Supervolcanos - large calderas - eruptions on enourmous scales

22 Yellowstone CalderaLake Taupo Campi Flegrei Supervolcanos Mt. Aso

23 Type of Eruptions

24 Eruption Types Subglacial Strombolian Vulcanian Peléan Hawai‘ian Phreatic Plinian

25 Subglacial Eruption Subglacial eruption: 1 water vapor cloud, 2 lake, 3 ice, 4 pillow lava, 5 magma conduit, 6 magma chamber - under ice or glacier - risk of floods, lahars - rare type (only 5 active) - e.g. Iceland

26 Strombolian Eruption - named after Mt. Stromboli - low level eruptions - ejection of cinder and lava bombs between 10 and a few 100m - viscous lava flows - gas bubbles (slugs) rise through magma and burst near the top - slugs form deep (~3km) and are hence difficult to predict - long lasting eruptions (up to decades)

27 Vulcanian Eruption Vulcanian eruption: 1 Ash plume, 2 Lapilli, 3 Volcanic ash rain, 4 Lava fountain, 5 Volcanic bomb, 6 Lava flow, 7 Sill, 8 Magma conduit, 9 Magma chamber, 0 Dike - named after Vulcano Island - rising magma makes contact with ground or surface water - extreme temperatures result in near instantaneous evaporation to steam  explosion - dangers from exploding steam, water, ash, rock, volcanic bombs

28 Peléan Eruption Pelean eruption: 1 Ash plume, 2 Volcanic ash rain, 3 Lava dome, 4 Volcanic bomb, 5 Pyroclastic flow, 6 Magma conduit, 7 Magma chamber, 8 Dike Mt. Mayon - named after Mt. Pelée - glowing cloud eruption - huge amounts of gas, dust, ash, lava fragments are blown out of a crater - fall back  avalanche down with 100mph (pyroclastic flows)

29 Hawai‘ian Eruption Hawaiian eruption: 1 Ash plume, 2 Lava fountain, 3 Crater, 4 Lava lake, 5 Fumaroles, 6 Lava flow, 7 Sill, 8 Magma conduit, 9 Magma chamber, 0 Dike - named after eruptions in Hawai‘i - occur along fissures, (central) vents - gentle, low level eruptions, lava fountains up to 600m high, - low viscosity lava - safest eruptions for tourism

30 Phreatic Eruption Mt. St. Helens - steam blast eruption - explosive expanding steam from ground or surface water - only pre-existing solid rock, no new magma is ejected - danger from steam, rock fragments, poisonous gases, asphyxiation - e.g. Mt. St. Helens before big eruption in 1980

31 Plinian Eruption Pinatubo - named after eruption of Vesuvius observed by Pliny the Younger - most powerful eruption type - explosive ejection of viscous lava - 10s of miles into the air (stratosphere) - 100s of miles fallout area - pyroclastic flows - large amounts of lava  caldera forming - e.g. Krakatoa, St. Helens, Pinatubo

32 Methods for Predictions

33 Predictions of Eruptions very difficult complex systems, highly non-linear every volcano is different significant progress in recent decades mostly by continued extensive monitoring can in many cases predict imminent (~days) eruptions combinations of different methods used

34 Methods for Predictions Seismic (earthquakes, tremors): short-period earthquakes like normal fault generated earthquakes indicate moving lava long-period earthquakes indicate increased gas pressure harmonic tremors indicate magma pushing on overlying rock increasing seismic activity  increasing probability of eruption but complex behaviour

35 Methods for Predictions Gas Emissions: Magma rises  gas escapes amount and chemical composition monitored e.g. increase in escaping gas volume observed before Pinatubo eruption e.g. decrease of escaping gas volume  sealing of gas passages  increase in pressure  higher eruption risk

36 Methods for Predictions Ground deformation: moving magma changes pressure inside the mountain  change in the slopes on the outside measured e.g. with tiltmeters (laser) Thermal Monitoring: IR maps to observe changes in surface temperature on-side detectors or satellite based Many major volcanos are monitored extensively to predict eruptions. These are volcanos in populated areas and potentially very dangerous ones (Yellowstone).

37 Dangers of Eruptions

38 Effects/Dangers Local (a few 10s of km‘s): explosions pyroclastic flows lava lahars gases (CO 2, H 2 S, SO 2 ) earthquakes

39 Effects/Dangers larger scales (10s to 1000s of km‘s): acid rain (covered earlier in course) SO 2  H 2 SO 4 tsunamies (covered later in course) ash-fallout global scales: volcanic winter, drop in temperatures due to change in albedo of Earth‘s atmosphere  crop failure, hunger, conflicts.....

40 Effects/Dangers - Examples on average all volcanos on Earth eject *10 11 kg CO 2 /yr all human emissions add up to about 2.5*10 13 kg/yr Mt. Pinatubo eruption ( ) >490 years after last known eruptive activity 2nd largest eruption in 20th century kg of magma ejected up to 34km high 2*10 10 kg SO 2 ejected coincided with typhoon Yunga  Lahars ash cloud km 2 10 times bigger eruption than Mt.St.Helens on ~800 people died, mostly due to roofs collapsing

41 Effects/Dangers - Examples

42

43 Supervolcanos: huge off-scale earthquakes tsunamies up to several 1000km 3 ejecta! immediate continent scale devastation mass extinction!!! next one due? Yellowstone

44 Effects/Dangers - Examples

45 Topics to Discuss in Seminar How to prevent danger for a large number of people in the first place? How to react in case of an imminent eruption? don‘t panic How to react in case of an eruption? run


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