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 of erupted material.
vent
cone
magma chamber
conduit
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Презентация на тему Volcanic Eruptions and Hazards
Содержание
- 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. Скачать презентацию
- 51. Похожие презентации
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 of erupted material. ventconemagma chamberconduit
Слайд 2
What is a volcano?
A volcano is a
The volcano includes the surrounding cone of erupted material.
Слайд 3
How 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 4
Explosive Eruptions
Mt. Redoubt
Explosive volcanic eruptions can be catastrophic
Erupt
10’s-1000’s km3 of magma
Send ash clouds >25 km into
the stratosphereHave severe environmental and climatic effects
Hazardous!!!
Above: Large eruption column and ash cloud from an explosive eruption at Mt Redoubt, Alaska
Слайд 5
Three products from an explosive eruption
Ash fall
Pyroclastic flow
Pyroclastic
surge
Explosive Eruptions
Pyroclastic flows on Montserrat, buried the capital city.
Слайд 7
Effusive Eruptions
Effusive eruptions are characterised by outpourings of
lava on to the ground.
Hawaii
Слайд 8
Practical Exercise 1.
What controls the violence of an
eruption?
How fast is magma ejected out of the
volcano?
Слайд 10
92,000 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 11
Pyroclastic flow
Lahars/Mud flows
Pyroclastic fall
Lava flow
Noxious Gas
Earthquakes
Volcanic Hazards
Courtesy of
www.swisseduc.ch
Слайд 13
Pompeii (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 14
Pompeii (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 15
Pompeii (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 16
Vesuvius 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 17 An eruption of Mt Peleé in 1902 produced
a pyroclastic flow that destroyed the city of St.
Pierre.before
after
Mt Peleé, Martinique (1902)
Слайд 23
Pyroclastic 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 24
Pyroclastic Fall
Ash load
Collapses roofs
Brings down power lines
Kills plants
Contaminates
water supplies
Respiratory hazard for humans and animals
Слайд 25
Lava Flow
It is not just explosive volcanic activity
that can be hazardous. Effusive (lava) activity is also
dangerous.
Слайд 26
Lava Flow - Heimaey, Iceland
Iceland, January 23,1973.
Large fissure
eruption threatened the town of Vestmannaeyjar.
Слайд 27
Lava 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 28
Lava 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 31
Volcano 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 32
Volcano Monitoring
Seismicity
Deformation
Gas Output
(on volcano and remote sensing
techniques)
These three things are the most important precursors to
an eruption.
Слайд 33
Seismic 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 34
Seismic 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 35
Deformation 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 36
Deformation 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 37
Gas 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 38
Gas Monitoring
Gas samples are collected from fumaroles
and active vents.
Gas levels may also be
monitored by remote sensing techniques
Слайд 39
In 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 40
Post-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 43
Noxious Gas
1,700 people living in the valley below
Lake Nyos in northwestern Cameroon mysteriously died on the
evening of August 26, 1986.
Слайд 44
Noxious 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 45
Noxious 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 48
Noxious 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 49
Earthquakes
Large volumes of magma moving through the shallow
