Volcanic Hazards. I.G.Kenyon

Transcription

1 Volcanic Hazards I.G.Kenyon

2 Volcanic disasters in perspective: Volcanic disasters of the 20 th century Eruption Victims and causes of death 1902, Mont Pelée, Martinique 29,000 (pyroclastic flows) 1902, Santa Maria, Guatemala >2000 (ashfall); >5000 (disease) 1911, Taal, Philippines 1400 (pyroclastic flows) 1919, Kelut, Indonesia 5000 (mud flows) 1929, Santiaguito, Guatemala 5000 (pyroclastic flows) 1930, Merapi, Indonesia 1400 (pyroclastic flows) 1951, Lamington, PNG 3000 (pyroclastic flows) 1982, El Chichón, Mexico >2000 (pyroclastic flows) 1985, Ruiz, Colombia 23,000 (mud flows) 1991, Pinatubo, Philippines 360 (ash fall); 140 (mud flows); 700 (disease)

3 Volcanic Hazards Summary Diagram

4 Primary Volcanic Hazards Lava Flows Pyroclastic Flows Ash and Tephra Fall Volcanic Gases

5 Lava Flows More of a threat to property than human life Basalt fissure eruptions are the most dangerous reaching speeds of over 50km per hour on steep slopes and can spread tens of kilometres from their source Andesitic and rhyolitic lavas move slowly and rarely spread more than 8km from their source

6 Lava Flows Paricutin, Mexico Remains of the city of San Juan de Parangaricutiro The church is one of the few buildings visible above the andesitic lava flows which covered 25 km² The city is located 5km away from the active vent

7 Lava Flows - Hawaii In Hawaii recent lava flows have buried roads, housing developments and cars. In one place, basalt almost completely submerged a parked (empty) school bus When lava at over 1000 C comes close to a house, the house erupts in flame. Usually people have time to get out of their way but not always with all their possessions

8 Lava Flows - Hawaii Kilauea in Hawaii has been erupting since 1983, covering 78 km² and destroying 180 houses but with no deaths The eruptions have also added 120 km² of new land and are a major tourist attraction

9 Lava Flows Garachico, Tenerife 1706 Eruptions occurred continuously from May 5 th until May 28 th. No-one was killed but people fled to the neighbouring town of Icod Lava poured in 7 separate cascades over the steep scarp above Garachico and completely filled the harbour The stronger basaltic flows buried orchards, blocked springs, set fire to many houses, overwhelmed the finest quarter of Garachico and spread into the sea as a fuming lobe The town was re-built over the next few decades more or less to the same town plan on the surface of the new lavas

10 La Garachico on the North Coast viewed from the road above (C820) The original town was largely destroyed in 1706 by lava erupted from the cone of Montana Negra 6.5km away and 1300 metres above the town The town has been re-built on the lava apron formed as the lava plunging down the cliff reached the sea

11 Lava Flows Laki, Iceland Largest recorded historical eruption Total volume of basalt extruded was 14.7 km³, covering an area of 565 km² A few churches, farms and homesteads were damaged but no-one was killed directly

12 Lava Flows Nyiragongo, Congo January 10 th 1977 Lava lake in Nyiragongo crater had been filling up for 50 years Lava lake just prior to the 1977 eruption A lava lake of basalt emptied following a large fissure-type eruption Initial speed of travel of lava flows were 100 km per hour Lavas covered 20km² and killed several hundred people and wildlife including a herd of elephants

13 Lava Flows Flood Basalt Eruptions Mega eruptions of basalt which have been correlated with mass extinctions in the geological record No Flood Basalts have occurred since man evolved just 4 million years ago Last Flood Basalt was 15 Ma in the Columbia River Plateau in the USA The volume of basalt erupted was 1,500 km³, some flows travelled up to 300km from their source

14 Lava Flows Flood Basalt Eruptions The Columbia River Plateau is a small Flood Basalt eruption compared to those erupted in India and Siberia 65 and 250 million years ago respectively The Deccan Trappes in India contain enough basaltic lava to cover the whole of the USA to a depth of 1 kilometre!

15 Flood basalt provinces: locations in red

16 Province Age (Myr) Volume (millions of km 3 ) Paleolatitude Duration (Myr) Columbia River 16 ± on ~ 1 (for 90%) Ethiopia 31 ± 1 ~ on ~ 1 North Atlantic 57 ± 1 > on ~ 1 K/T? Flood basalt provinces: flood for thought Deccan 66 ± 1 > os ~ 1 Madagascar 88 ± 1? 45 os ~ 6? Rajmahal 116 ± 1? 50 os ~ 2 Serra Geral/ Etendeka 132 ± 1 > os ~ 1 or ~ 5? Antarctica 176 ± 1 > os ~ 1? Karoo 183 ± 1 > os Newark 201 ± 1 >1.0? 30 on ~ 0.6 Siberian 249 ± 1 > on? ~ 1

17 Pyroclastic Flows A mixture of hot rock fragments, lava particles and ash buoyed up by hot gases Often called Nuées Ardentes or glowing fire-clouds Associated with andesitic and rhyolitic volcanoes and the collapse of lava domes Can move at high speeds up to 300 km per hour and can extend up to 40km from their source Temperatures within the flow are commonly C

18 Redoubt Volcano-Alaska with a growing Lava Dome February 1990 Lava Dome on the North face of Redoubt Volcano The lava dome was destroyed by an eruption on February 15 th 1990 which generated a pyroclastic flow

19 Pyroclastic Flow Augustine Volcano, Alaska 1986 Geologist inspects the pyroclastic flow, note the wide range of particle sizes all deposited together

20 Pyroclastic Flows Mount Pelée 1902 Only 64 known survivors from 29,000 inhabitants of the port of St.Pierre Many sources state only 1 or 2 survivors which is now known to be incorrect following the publication of La Catastrophe by Alwyn Scarth A pyroclastic flow was generated on May 8 th 1902 which sped down the River Blanche valley at a speed in excess of 190 km/hr

21 Pyroclastic Flows Mount Pelée 1902

22 Pyroclastic Flows Mount Pelée 1902 The pyroclastic flow has been estimated at 700 C which was hot enough to melt glass and metal Further Nuées Ardentes occurred on May 20 th and also August 30th 1902 killing another 2000 people

23 Pyroclastic Flows Mount Pelée 1902 A famous survivor of St.Pierre was Louis-Auguste Ciparis, a prisoner who had been put into solitary confinement in a small cell built like a bomb shelter The structure still survives today

24 Pyroclastic Flows Mount Pelée 1902 Left, the 25 year old Louis- Auguste Ciparis still quite badly burned a month after his release from prison Below, drinking glasses partially melted by the fires that raged in St.Pierre after the Nuée Ardente on May 8 th 1902

25 Pyroclastic Flows Mt. St.Helens May 1980 Before the eruption of May 1980

26 Pyroclastic Flows Mt. St.Helens May 1980 New lava dome beginning to form After the Eruption of May 1980

27 Pyroclastic Flows Mt. St.Helens May 1980 Northern flank of the mountain rose 150m under the force of magma rising inside A near surface earthquake magnitude 5.1 caused the collapse of the northern slope The avalanche and associated explosion decapitated the cone and created a crater 600m deep and 2km in diameter The pyroclastic flow was dubbed the Stone Wind by the media and it reportedly travelled at supersonic speed and had a temperature of 250 C

28 Pyroclastic Flows Mt. St.Helens May km² of forestry was devastated by the pyroclastic flows Close to the volcano, full grown Douglas Fir trees were blasted off their stumps At 30 km away the trees were pushed over and oriented parallel to one another

29 Pyroclastic Flows Mt. St.Helens May km away from the eruption of Mount St.Helens

30 Pyroclastic Flows Mt. St.Helens May 1980 The pyroclastic flow contained large boulders up to 1 metre in diameter Large bulldozer wrecked by the pyroclastic flow of May 18 th 1980

31 Pyroclastic Flows Mt. St.Helens May 1980 Before After The same marker pole

32 Volcanic Dust, Ash and Tephra Dust Pyroclastic air fall material <0.5mm in diameter Ash Pyroclastic air fall material <2mm in diameter Tephra Pyroclastic air fall material >2mm in diameter

33 Volcanic Dust, Ash and Tephra Ash build up on roofs can lead to their collapse 300 people were killed by this method during the eruption of Mount Pinatubo, Philippines 1991 Ash infiltrates machinery and quickly wears out any moving parts Fine ash from an eruption is hazardous to aircraft-when heated inside a jet engine it creates a liquid that sprays around the turbine and sets as a glassy coating which blocks the airflow and shuts down the engine. Nine jets had to make emergency landings during the month after the 1991 Pinatubo eruption having flown into the ash cloud

34 Problems created by air fall ash deposits Japan following Mt.Unzon eruption The Philippines after Pinatubo erupted Montserrat after Souffriere Hills erupted The Philippines after Pinatubo erupted

35 Ash deposits from Galunggung, Java, August 1982 Toxic chemicals in the ash may poison the soil Terraced fields covered in ash buries and kills crops leading to local food shortages

36 Ash fall can turn day into night and make driving hazardous Ash and dust inhalation leads to respiratory problems Ash from Galunggung, Java Shopping in Washington State May 1980

37 Volcanic Gases - Hawaii

38 Volcanic Gases Laki, Iceland Basaltic lavas 14.7 km³ in volume also emitted 8 million tonnes of fluorine gas About 122 million tonnes of sulphur dioxide was released in columns that rose 6-13 km high and generated 250 million tonnes of sulphuric acid aerosols that remained aloft for about 2 years

39 Volcanic Gases Laki, Iceland Fluorine gas contaminated pastures and over 75% of the sheep and horses plus around 50% of the cattle died Crops failed, famine ensued and over 20% of Iceland s population died The aerosol spread as a blue fog and caused crop failure in Ireland and Scandinavia The aerosol also caused three long and abnormally cold winters in the northern hemisphere from autumn 1783 to spring 1786

40 Two-stage degassing in flood lavas

41 Laki plume transport in first month Polar jet stream

42 Temperature anomalies in NW Europe July 1783 temperature deviations from the mean (in K)

43 Volcanic aerosol Pinatubo sunset over Hawaii

44 Optical phenomena & weather effects following the eruption of Tambora 1815 T Cobbley et al. William Turner. Amazing skies, England, Pendennis Castle, Cornwall; Scene after a Wreck. c.1816

45 Volcanic Gases Lake Nyos, Cameroon August 21 st 1986 Lake Nyos is a small but deep lake filling the crater of an active hot spot volcano in Cameroon, West Africa

46 Volcanic Gases Lake Nyos, Cameroon August 21st 1986 Lake Nyos is 1km wide and 200m deep and fills the crater of a hot spot volcano Because of its depth, the cool bottom waters do not mix with the warmer surface waters For many years the two waters remained separate from each other During this time carbon dioxide slowly bubbled out of cracks in the crater floor and dissolved in the cool bottom water

47 Volcanic Gases Lake Nyos, Cameroon August 21st 1986 By August 21 st 1986 the bottom water had become supersaturated with carbon dioxide On that day, perhaps due to an earthquake or storm, the lake burped, expelling huge bubbles of carbon dioxide (1 cubic km of gas) The gas being denser than air flowed down the flank of the volcano and spread out over the countryside for about 23km before dispersing The gas cloud engulfed the village of Nyos killing 1,742 people and around 6,000 head of cattle

48 Volcanic Gases Lake Nyos, Cameroon 1986 Cattle near Lake Nyos, Cameroon, West Africa, fell where they stood, victims of a cloud of carbon dioxide

49 Volcanic Gases Nyamuragira Volcano, Zaire Dog skeleton found on the southern flank of Nyamuragira volcano in a Mazuku a Swahili word for a pocket of carbon dioxide gas

50 Volcanic Gases Volcanic Smog (Vog) - Hawaii High pressure cold dense air is descending Volcanic gases are unable to escape through it and accumalate as a volcanic smog (vog) a few hundred metres above the ground

51 Secondary Volcanic Hazards Lahars Volcanic Landslides Tsunamis

52 Lahars Volcanic Mudflows Volcanic ash mixes with water to form a dense slurry similar to freshly mixed concrete The slurry known as a lahar can flow downslope at over 50 km per hour The water may be derived from melted snow and ice from the upper part of the volcano, from heavy rainfall or from the collapse of a crater lake

53 Lahars Nevado del Ruiz, Colombia 1985 Armero The town of Armero in Colombia was overwhelmed by lahars from the Nevado del Ruiz volcano Although more than 20 km away from the volcano over 22,000 people were killed in Armero buried alive in the 8m deep lahars that travelled at speeds of up to 45 km per hour

54 Lahars Nevado del Ruiz, Colombia 1985 The eruption melted the ice cap as it was showered with hot pyroclastic debris and released between 10 and 60 million cubic metres of water 90% of all buildings in the town were destroyed, replaced by a 5-8 metre thick layer of mud which now entombs the bodies of around 25,000 people and 15,000 animals

55 Lahars Volcanic Mudflows Armero Armero Bridge destroyed by a lahar from Mount St.Helens, Washington State, USA Armero

56 Lahars Redoubt Volcano, Alaska Section through 3 successive lahars, material ranges in size from mud through sand and up to boulders

57 Lahars Redoubt Volcano, Alaska Mouth of the Drift River, Alaska, house buried by a lahar

58 Lahars Redoubt Volcano, Alaska 1990 Large block of glacier ice carried many kilometres downstream by lahars in the eruption sequence

59 Lahars Redoubt Volcano Alaska 1990 On February 15th 1990 containment berms at the Drift River Oil Terminal were over-run by a lahar These tanks escaped damage but a total of $160 million in damages to petroleum installations occurred nearby

60 Tsunamis Generated by explosive eruptions on volcanic islands or by submarine caldera collapse Waves generated may reach tens of metres up to 100 metres in height Most of the 36,000 deaths attributed to the 1883 eruption of Krakatoa were not due to ash or lava, but to tsunamis that slammed into nearby coastal towns

61 Submarine volcanic eruption, caldera collapse or volcanic landslide Tsunamis

62 Tsunamis Krakatoa 1883 After Before Eruptions followed by caldera collapse Maps showing islands in the Krakatau group before and after the eruption The eruption sequence generated many tsunamis, between 30 and 40 metres in height which are reported to have moved at an average speed of 60 mph

63 Tsunamis Krakatoa 1883 All coastal towns and villages on the Sunda Strait were destroyed within 2 hours of the explosion and collapse of the volcano The waves were so powerful that blocks of coral weighing up to 600 tonnes were thrown onto the shore The warship Berouw was carried 3km inland and deposited at an elevation of 10 metres above sea level

64 Tsunamis Krakatoa 1883 The Royal dutch Navy s armed paddle steamer Berouw about to be picked up by one of the large tsunamis generated by the eruption The warship Berouw, well and truly stranded 3km up the Koeripan River. Hunks of rusting iron remained in the jungle until the 1980s.

65 Evidence of Past Tsunamis-The Sediment Record Tsunami Deposit

66 Tsunamis The impact on low-lying coastlines

67 Volcanic Landslides Ground deformation of volcanic slopes by rising magma may also cause instability and trigger landslides before an eruption These are gravity-driven slides of masses of rock and loose volcanic material Often occur during an eruption, as with Mount St.Helens when the North side of the volcano collapsed Landslides can occur at other times on volcanic craters as a result of heavy rainfall or earthquakes A chaotic tumbling flow of material is termed a debris avalanche

68 Shaded relief view of the Canaries from the West Arrows indicate debris avalanche deposits from giant landslides

69 Volcanic Landslides - Tenerife The Orotova and Guimar Valleys Both are 10km wide with smooth floors sloping gently seawards The landslides that formed them displaced more than 100km³ of lavas with a total thickness of m These displaced lavas now lie on a layer of chaotic breccia and sandy clay that was crushed when the volcanic materials slid over them

70 Volcanic Landslides -Tenerife volcanic landslides Figures refer to dates of eruptions

71 The End Eruption cloud of Redoubt Volcano, Alaska April 21 st 1990