3.1 Volcanoes

Question 1

What are the different plate boundaries?

Answer 1

There are 4 different plate boundaries:

• Convergent (Subduction) - Where the denser oceanic plate is forced below the less dense continental plate and it sinks below into the mantle.
• Convergent (Collision) - Where two continental plates of equal density meet and are forced upwards.
• Constructive - Where two plates are move away from each other and magma from the mantle rises up to form new crust
• Conservative - Where two plates are sliding past each other, either at different directions or speeds.

Question 2

Describe the characteristics of a Composite Volcano

Answer 2

Characteristics of a composite volcano are:

• Steep slope gradient due to having high viscosity lava so it hardens quickly before spreading far.
• Erupt much less frequently and predictably and these eruptions are much more explosive.
• Eject ash, rock, gases, steam and lava due to its explosive eruptions which destroy more of the volcano producing more ash.
• Made from layers of lava and ash, they are sometimes called stratovolcanoes referring to layers.

Examples include: Mount Fuji in Japan and Mount Shasta in California

Question 3

Describe the characteristics of a Shield Volcano

Answer 3

Characteristics of a shield volcano are:

• Gentle slopes due to having low viscosity lava so it spreads a far before hardening.
• Erupt frequently and these eruptions are gentle (effusive).
• Eject just steam and lava due to its more gentle eruption therefore it can’t destroy much of the volcano and it can’t eject much ash and rock.
• Made from layers of just lava

Examples include: Mauna Kea and Mauna Loa in Haiwaii

Question 4

Describe the formation of a composite Volcano

Answer 4

Composite volcanoes are mostly commonly found on subductive plate boundaries. As the Oceanic plate sinks below into the mantle its melts and becomes magma. This magma is impure and contains lots of elements, water and gases which lead to this magma rising. Once it reaches the crust it finds its way into cracks and will accumulate pressure. Once enough pressure builds up the gases and magma erupt from the surface. First lava flows and solidifies and after the ash settles on top. This cycle is repeated again and again and layers of lava and ash build up.

Question 5

Describe the formation of Shield Volcano

Answer 5

Shield volcanoes are most commonly found on constructive plate boundaries. As the plates separate it opens a gab in the crust for magma to rise up from. These results in an effusive eruption meaning the balsatic lava which is less viscous gently flows outwards and spreads far before it solidifies. This results in shorter wider based volcanoes

Question 6

Describe the distribution of Volcanoes

Answer 6

Volcanoes are most commonly found on constructive plate boundaries and convergent (subduction) plate boundaries. They are found most densely around the Pacific ring of fire

Volcanoes can also be found on Volcanic hotspots. These are superheated plumes underneath plates, this forms shield volcanoes on the surface as the super heated magma melts the crust

Question 7

How are volcanic Eruptions measured?

Answer 7

Volcanic eruptions are measured using the volcanic explosivity index which categorises volcanic activity based on the volume of Tephra that is erupted. This has limitations as id doesn’t take into account other volcanic hazards such as pyroclastic flows.

Question 8

Name and describe some volcanic hazards

Answer 8

Primary hazards:
- Lava flows - Streams of molten rock. Low viscosity flows can extend for tens of kilometres and travel at up to 10km/hr

• Pyroclastic flows - High-density mixtures of hot, dry rock fragments and hot gases – essentially a turbulent cloud of ash between 200-700°C in temperature that moves at 80km/hr +. They flow close to ground due to their high-density.
• Ash fall - Fragments of volcanic rock and lava blasted into the air by explosions and carried upwards by hot gases
• 2mm-1cm in diameter. Can travel hundreds of thousands of miles
• Volcanic gases - Escape of gases dissolved in magma - Released by pressure drop as magma rises - H²O, CO², SO².

Secondary hazards:
- Lahars - Mixture of water and fine rock fragments. Caused by melting snow and ice, by intense rainfall, or by landslides - Looks like a mass of wet concrete - Carriers rock debris; boulder up to 10m in diameter. They range in size and speed, and constantly change – generally increasing in both. They erode rock debris as they go, growing in size

• Landslides - Rock and soil that falls, slides or flows under the force of gravity. Mixtures of debris move in a wet or dry state (or both). May transform into a lahar if they contain enough water and fine material. 1km³ - 100km³ in size, >100km/hr in speed
• Tsunamis - Giant sea waves caused by large-scale and sudden disturbance of the sea water. Most are secondary hazards from earthquakes or volcanic activity. Nearly all result from large and rapid vertical uplift of the sea floor. Some caused by explosion of volcanic islands and landslides or rockfalls.

Question 9

What are the short term impacts of a volcanic eruption?

Answer 9

Short term impacts:
- Air travel disruption due to ash cloud
- Immediate volcanic hazards lead to loss of life and damage infrastructure
- Large eruptions can inject significant amounts of ash and sulfur dioxide into the atmosphere, leading to short-term cooling of the climate.

Question 10

What are the long term Impacts of a volcanic eruption

Answer 10

Long term impacts:
- Health effects - fine ash can lead to respiratory damage and being displaced due to an eruption can negatively impact mental health.
- Communities may implement new initiatives and infrastructure to become more resilient to eruptions
- Volcanic ash and lava can weather and enrich the soil, leading to the formation of fertile agricultural land.