'chimney' that connects molten rock (magma) from within the Earth’s
crust to the Earth's surface.The volcano includes the surrounding cone of erupted material.
vent
cone
magma chamber
conduit
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Volcanic Eruptions and Hazards
Содержание
- 1. Volcanic Eruptions and Hazards
- 2. What is a volcano? A volcano is
- 3. How and why do volcanoes erupt?Hot, molten
- 4. Explosive EruptionsMt. RedoubtExplosive volcanic eruptions can be
- 5. Three products from an explosive eruptionAsh fallPyroclastic
- 6. Direct measurements of pyroclastic flows are extremely dangerous!!!
- 7. Effusive EruptionsEffusive eruptions are characterised by outpourings of lava on to the ground.Hawaii
- 8. Practical Exercise 1.What controls the violence of
- 9. Volcano Monitoring and Hazard Mitigation
- 10. 92,000 Tambora, Indonesia 181536,000 Krakatau, Indonesia 188329,000
- 11. Pyroclastic flowLahars/Mud flowsPyroclastic fallLava flowNoxious GasEarthquakesVolcanic HazardsCourtesy of www.swisseduc.ch
- 12. Pyroclastic FlowFor example, eruption of Vesuvius in 79 AD destroyed the city of Pompeii
- 13. Pompeii (79AD) On August 24, 79AD Mount Vesuvius
- 14. Pompeii (79AD) Pyroclastic flows of poisonous gas and
- 15. Pompeii (79AD) The cities remained buried and undiscovered
- 16. Vesuvius todayVesuvius remains a hazardous volcano with
- 17. An eruption of Mt Peleé in 1902
- 18. 29,000 people died…. Only 2 survived! Why?
- 19. How do pyroclastic flows cause devastation?
- 20. Pyroclastic Flow - direct impactCourtesy of www.swisseduc.ch
- 21. Pyroclastic Flow - burial
- 22. Pyroclastic Flow - burns
- 23. Pyroclastic Flow - laharsHot volcanic activity can
- 24. Pyroclastic FallAsh loadCollapses roofsBrings down power linesKills plantsContaminates water suppliesRespiratory hazard for humans and animals
- 25. Lava FlowIt is not just explosive volcanic
- 26. Lava Flow - Heimaey, IcelandIceland, January 23,1973.Large fissure eruption threatened the town of Vestmannaeyjar.
- 27. Lava Flow - Heimaey, IcelandThe lava flows
- 28. Lava Flow - Heimaey, IcelandHowever, the potential
- 29. Practical Exercise 2.Assessing Volcanic Hazards
- 30. So….How do we minimize the risk of active volcanoes?
- 31. Volcano MonitoringVolcano Observatories are set up on
- 32. Volcano MonitoringSeismicityDeformationGas Output (on volcano and remote
- 33. Seismic ActivityEarthquake activity commonly precedes an eruptionResult
- 34. Seismic ActivityEarthquake activity is measured by SeismographsSeismographs
- 35. Deformation Monitoring“Tiltmeters” are used to measure the
- 36. Deformation MonitoringTilltmeters can tell you when new
- 37. Gas MonitoringCommonly gas output from a volcano
- 38. Gas Monitoring Gas samples are collected from
- 39. In Summary..Volcanoes are extremely hazardous. However, the
- 40. Post-lecture Question:What should geologists do about volcanic
- 41. Additional (Optional) Material
- 42. Are there other volcano related hazards?
- 43. Noxious Gas1,700 people living in the valley
- 44. Noxious GasLake Nyos is a crater lake
- 45. Noxious GasA management plan has been developed
- 46. Noxious Gas
- 47. Noxious Gas
- 48. Noxious GasThe Lake Nyos incident was not
- 49. EarthquakesLarge volumes of magma moving through the
- 50. EarthquakesDestruction after a volcanic induced earthquake in Japan
- 51. Скачать презентанцию
What is a volcano? A volcano is a vent or 'chimney' that connects molten rock (magma) from within the Earth’s crust to the Earth's surface. The volcano includes the surrounding cone
Слайды и текст этой презентации
Слайд 2What is a volcano?
A volcano is a vent or
The volcano includes the surrounding cone of erupted material.
Слайд 3How and why do volcanoes erupt?
Hot, molten rock (magma) is
buoyant (has a lower density than the surrounding rocks) and
will rise up through the crust to erupt on the surface.Same principle as hot air rising, e.g. how a hot air balloon works
When magma reaches the surface it depends on how easily it flows (viscosity) and the amount of gas (H2O, CO2, S) it has in it as to how it erupts.
Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption!
Think about shaking a carbonated drink and then releasing the cap.
Small amounts of gas and (or) low viscosity (runny) magma will form an effusive eruption
Where the magma just trickles out of the volcano (lava flow).
Слайд 4Explosive Eruptions
Mt. Redoubt
Explosive volcanic eruptions can be catastrophic
Erupt 10’s-1000’s km3
of magma
Send ash clouds >25 km into the stratosphere
Have severe
environmental and climatic effectsHazardous!!!
Above: Large eruption column and ash cloud from an explosive eruption at Mt Redoubt, Alaska
Слайд 5Three products from an explosive eruption
Ash fall
Pyroclastic flow
Pyroclastic surge
Explosive Eruptions
Pyroclastic
flows on Montserrat, buried the capital city.
Слайд 7Effusive Eruptions
Effusive eruptions are characterised by outpourings of lava on
to the ground.
Hawaii
Слайд 8Practical Exercise 1.
What controls the violence of an eruption?
How
fast is magma ejected out of the volcano?
Слайд 1092,000 Tambora, Indonesia 1815
36,000 Krakatau, Indonesia 1883
29,000 Mt Pelee, Martinique
1902
15,000 Mt Unzen, Japan 1792
Volcanic Fatalities
But, volcanoes cause fewer fatalities
than earthquakes, hurricanes and famine.Courtesy of www.swisseduc.ch
Слайд 11Pyroclastic flow
Lahars/Mud flows
Pyroclastic fall
Lava flow
Noxious Gas
Earthquakes
Volcanic Hazards
Courtesy of www.swisseduc.ch
Слайд 13Pompeii (79AD)
On August 24, 79AD Mount Vesuvius literally blew its
top, erupting tonnes of molten ash, pumice and sulfuric gas
miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas.
Слайд 14Pompeii (79AD)
Pyroclastic flows of poisonous gas and hot volcanic debris
engulfed the cities of Pompeii, Herculaneum and Stabiae suffocating the
inhabitants and burying the buildings.
Слайд 15Pompeii (79AD)
The cities remained buried and undiscovered for almost 1700
years until excavation began in 1748. These excavations continue today
and provide insight into life during the Roman Empire.
Слайд 16Vesuvius today
Vesuvius remains a hazardous volcano with heavily populated flanks:
around 1.5 million people live in the city of Naples
aloneNaples is situated approx. 30 km from Vesuvius
Pyroclastic flows can flow up to 100 km from source!
Bay of Naples
Vesuvius
Naples
Courtesy of www.swisseduc.ch
Слайд 17An eruption of Mt Peleé in 1902 produced a pyroclastic
flow that destroyed the city of St. Pierre.
before
after
Mt Peleé, Martinique
(1902)
Слайд 23Pyroclastic Flow - lahars
Hot volcanic activity can melt snow and
ice
Melt water picks up rock and debris
Forms fast flowing, high
energy torrentsDestroys all in its path
Слайд 24Pyroclastic Fall
Ash load
Collapses roofs
Brings down power lines
Kills plants
Contaminates water supplies
Respiratory
hazard for humans and animals
Слайд 25Lava Flow
It is not just explosive volcanic activity that can
be hazardous. Effusive (lava) activity is also dangerous.
Слайд 26Lava Flow - Heimaey, Iceland
Iceland, January 23,1973.
Large fissure eruption threatened
the town of Vestmannaeyjar.
Слайд 27Lava Flow - Heimaey, Iceland
The lava flows caught the inhabitants
by surprise
Before the eruption was over, approximately one-third of the
town of Vestmannaeyjer had been destroyed
Слайд 28Lava Flow - Heimaey, Iceland
However, the potential damage was reduced
by spraying seawater onto the advancing lava flows.
This caused
them to slow and/or stop, or diverted them away from the undamaged part of the town.
Слайд 31Volcano Monitoring
Volcano Observatories are set up on all active volcanoes
that threaten the human population. These are designed to monitor
and potentially to predict the eruptive behaviour of the volcano in question.
Слайд 32Volcano Monitoring
Seismicity
Deformation
Gas Output
(on volcano and remote sensing techniques)
These three
things are the most important precursors to an eruption.
Слайд 33Seismic Activity
Earthquake activity commonly precedes an eruption
Result of magma pushing
up towards the surface
Increase volume of material in the volcano
shatters the rockThis causes earthquakes
Слайд 34Seismic Activity
Earthquake activity is measured by Seismographs
Seismographs are stationed on
the flanks of the volcano
These record the frequency, duration and
intensity of the earthquakes and report it back to the volcano observatory.
Слайд 35Deformation Monitoring
“Tiltmeters” are used to measure the deformation of the
volcano
The tiltmeters measure changes in slope as small as one
part per million. A slope change of one part per million is equivalent to raising the end of a board one kilometer long only one millimeter!
Слайд 36Deformation Monitoring
Tilltmeters can tell you when new material enters the
magma chamber.
Note the presence of earthquakes in relation to the
deformation. Often it is a combination of events that fore-warns of an eruption.A
B
Слайд 37Gas Monitoring
Commonly gas output from a volcano increases or changes
composition before an eruption.
As magma rises to the surface it
releases (exsolves) much of its gas content.This can be measured
Слайд 38Gas Monitoring
Gas samples are collected from fumaroles and active
vents.
Gas levels may also be monitored by remote
sensing techniques
Слайд 39In Summary..
Volcanoes are extremely hazardous.
However, the volcano can be
studied, monitored and understood.
Each volcano is different, and offers a
unique set of dangersPlans may be emplaced to help control potential damage.
Слайд 40Post-lecture Question:
What should geologists do about volcanic eruptions in the
future?
Study volcanoes to find out more about how and why
they eruptMonitor the volcanoes
Develop hazard mitigation plans
Understand the population around volcanoes, i.e. why do people choose to live near volcanoes?
Education
Слайд 43Noxious Gas
1,700 people living in the valley below Lake Nyos
in northwestern Cameroon mysteriously died on the evening of August
26, 1986.
Слайд 44Noxious Gas
Lake Nyos is a crater lake inside a dormant
volcano.
The lake had become laden with carbon dioxide gas.
This
gas had suddenly bubbled out of the lake and asphyxiated nearly every living being in the surrounding valley.
Слайд 45Noxious Gas
A management plan has been developed to remove gas
from the lake to prevent a further tragedy.
An artificial vent
to the lake surface was created with pipe.Water is pumped from the bottom of the lake to the surface through the pipe, where it can degas.
Слайд 48Noxious Gas
The Lake Nyos incident was not unique.
Two years
earlier, Lake Monoun, 60 miles to the southeast, released a
heavy cloud of toxic gas, killing 37 people.A third lake, Lake Kivu, on the Congo-Rwanda border in Central Africa, is also known to act as a reservoir of carbon dioxide and methane, which is a valuable natural gas that is gathered from the lake and used locally.
Слайд 49Earthquakes
Large volumes of magma moving through the shallow crust can
cause large earthquakes.
This can lead to building collapse, slope failure
and avalanches
