Tectonic Processes & Hazards - EQ1 - 1.3B - Volcanoes Flashcards
To be a hazard, it must..
affect people in some way, for example how damage of livestock affects the farmer and food supplies
In most cases, only …………………………… found at ………………………… represent a significant tectonic hazard.
In most cases, only large composite volcanoes found at destructive plate margins represent a significant tectonic hazard.
In most cases, only large composite volcanoes found at destructive plate margins represent a significant tectonic hazard. These eruptions often have…
- lava flows, pyroclastic flows, lahars and extensive ash and tephra fall that can affect areas up to 30 km from the volcanic event
Give a case study for the hazard of ash clouds
(79 AD) Mount Vesuvius, Italy
What was the danger of ash clouds in the case study of Mount Vesuvius
- Population can be poisoned by the deadly gas and
- subsequently buried under meters of ash during eruption
Give a case study for the hazard of steam eruptions and mud flows
Mount Rainier, Washington (1984)
What was the danger of steam eruptions and mudflows in the case study of Mount Rainier, Washington (1984)
- Mixtures of volcanic debris and water as heat from the volcano melts ice on the mountain
- The melted ice can run down the mountain inundating the land and washing away buildings
Give a case study for the hazard of pyroclastic flows
Mount Merapi, Indonesia (2010)
What was the danger of pyroclastic flows in the case study of Mount Merapi, Indonesia (2010)
- Pyrocastic flows send floods of hot rocks and gas down the mountain’s steep flanks- incinerating anything in the path population and buildings.
Give a case study for the hazard of lava flows
Mount Nyiragongo, Congo (2002)
What was the danger of lava flows in the case study of Mount Nyiragongo, Congo (2002)
- The laval flow forces people to evacuate and leaves people homeless due to the collapsed destroyed buildings
What are primary hazards from volcanoes?
- lava flows
- pryoclastic flows
*tephra and ash falls - gas eruptions
What are secondary hazards from volcanoes?
- lahars
- Jökulhlaups
Where do lava flows occur
- subduction zone volcano (composite)
- hot-spot volcano (shield type)
What are lava flows
- Streams of lava that have erupted from a volcano onto the Earth’s surface
- They are very hot (reaching up to 1170°C) and can take years to cool completely
- Extensive areas of solidified lava can extend several kilometres from volcanic vents if the lava is basaltic and low viscosity
- It can flow at up to 40 km/h
What is the danger posed by lava flows
- Lava flows are generally not a threat to humans, because most of them move so slowly that people can easily get out of their way. * Nevertheless, they do destroy everything in their path so settlements can be lost
……….. are considered to be the most dangerous volcanic hazard
Pyroclastic flows
What are pyroclastic flows
- Flows consist of a dense mixture of superheated tephra (extremely hot up to 700°C)
- and poisonous gases erupted from a crater, moving down the sides of volcanoes and into the surrounding area at great speed (up to 700 km/h).
What is the danger of pyroclastic flows
- Any buildings or people in the way are destroyed through impact, burying, incineration or poisoning
- but because they move so quickly, they are far more dangerous than lava flows
- The deposition of material may also block river channels and cause flooding
Where do pyroclastic flows occur
- Subduction zone volcano (composite)
What is tephra
Tephra are pieces of volcanic rock and ash that blast into the air during volcanic eruptions.
What is ash
- The smallest fragments erupted from a volcano
- Ash can be forced to a high altitude and are so light that they can be carried around the planet in the atmosphere.
What is the danger of ash
- Ash falls are very disruptive
- Where the ash lands, it covers everything causing poor visibility and slippery roads
- Roofs may collapse under the weight, and engines may get clogged up and stop working (as was the fear with the Eyjafjallajökull ash cloud)
- Ash clouds disrupt flight paths of aeroplanes as it damages engines and fuselages.
What is the danger of tephra
- The larger pieces tend to fall near the volcano, where they can cause injury or death (as well as damaging structures).
What do tephra and ash falls occur
- Constructive plate margin volcanoes (cinder cone, fissure eruption)
- Subduction zone volcano (composite)
What are gas erruptions
- Magma contains dissolved gases that are released into the atmosphere during a volcanic eruption (some of which are a potential hazard to people, animals and structures).
- The volcanic gases include water vapour (about 80%), carbon dioxide and sulphur dioxide.
- Once in the air, the gases can travel for thousands of kilometres
What is the danger posed by water vapour in gas erruptions
may condense locally and mix with other erupted material e.g lahars
What is the danger posed by suphur dioxide in gas erruptions
- poisonous in high concentrations, and can cause ‘acid rain’ when combined with water vapour, damaging buildings and plants.
- SO2 may also cool the Earth when it is carried high into the atmosphere by blocking the Sun’s heat energy:
- historical eruptions have caused crop failures and famine in this way
Where do gas erruptions occur
- Subduction zone volcanoes (composite)
- Hot-spot volcano (shield)
What are lahars
- These are a mixture of water and erupted volcanic material of various sizes, which flow very fast (60 km/h) down river valleys
- They vary in size and speed
- The largest can be hundreds of metres wide and can flow at tens of metres per second - again, too fast for people to outrun.
What causes Lahars
- They are caused when an eruption quickly melts snow and ice
- Or, alternatively, heavy rainfall during or after an eruption erodes loose rock and soil - causing it to surge downslope
What is the danger of lahars
- These are a major hazard along valleys as this is usually where settlements and people are located, and those living some distance from an erupting volcano may feel that they are safe,
- but lahars move so quickly over long distances that they can be difficult to escape
Where do lahars occur
Subduction zone volcanoes (composite)
What are Jokulhaups
- floods caused by a sudden release of water and rocks when glacial ice is melted by the eruption
Give a detailed explanation of Jokulhaups
- Where a volcano erupts underneath an ice cap, the heat will melt some of the ice
- The meltwater builds up around the top of the volcano, trapped by the surrounding ice
- Eventually the warm meltwater will melt and lift the ice away from the ground, and then the water bursts out from under the ice and flows rapidly to lower ground
- When this happens anything in its path is washed away or covered by volcanic and glacial deposits carried in the jokulhlaup
What is the threat of jokulhlaups
- These floods can be very dangerous, because they suddenly release large amounts of water, rock, gravel and ice that can catch people unawares, and flood and damage land and structures
Where do Jökulhlaups occur
Constructive plate margin volcanoes (cinder cone, fissure eruption)
What was the VEI score of the Mount St.Helens eruption
5
What was the danger/ destrcution of the Mount St.Helens Erruption
- avalanches
- 57 died
- ash 10 miles into sky —> communities 60 miles away in darkness
- 520 million tons of gas over world
- largest lanslide ever recorded
