Tectonics Pack C

Question 1

What magma properties does the type of volcano depend on?

Answer 1

• Viscosity/stickiness
• Amount of gas
• Composition
• Way in which it reaches the surface

Question 2

What are the two types of volcano?

Answer 2

• Shield volcano
• Stratovolcano

Question 3

What are the properties of a shield volcano?

Answer 3

• Formed by low viscosity, runny lava
• Basaltic lava
• Spreads far from source to form a volcano with gentle slopes
  E.g. Mauna Kea and Mauna Loa (world’s largest active volcanoes rising 9km above sea floor)

Question 4

What are the properties of a stratovolcano?

Answer 4

• Steep sided and cone shaped
• Formed from viscous, sticky lava that doesn’t flow easily
• Lava builds up around the vent
• Explosive eruptions due to gas buildups
• Andesitic lava

Question 5

What is a volcanic hazard?

Answer 5

Any potentially dangerous volcanic process that puts human lives, livelihoods or infrastructure at risk of harm

Question 6

What are the different types of eruption?

Answer 6

Order of increasing explosivity…
- Icelandic (effusive)
- Hawaiian (effusive)
- Strombolian (explosive)
- Vulcanian (explosive)
- Vesuvian (explosive)
- Plinian (explosive)

Question 7

What are the hazards associated with volcanic eruptions?

Answer 7

• Tephra
• Ash
• Toxic gases
• Lava
• Pyroclastic flows
• Landslides/debris avalanches
• Lahars
• GLOFs (jokulhlaups)
• Tsunamis

Question 8

What is ash and tephra?

Answer 8

• Tephra is the catch all term to describe all erupted clasts regardless of size
• Ash is particles less than 2mm in size
• Ash is made up of small, sharp, angular fragments of glass and other volcanic rock

Question 9

How is ash and tephra a hazard?

Answer 9

• Falls to ground around volcano
• Loads building roofs and obscures road marking (difficult to travel)
• Burial of plants and stripping of branches from loading on vegetation (harms agriculture)
• Fine-grained nature of ash means it is easily transported by winds or up into stratosphere (cooling)
• Abrasive nature of ash can damage aircrafts

Question 10

How are gases a hazard?

Answer 10

• Exposure to harmful gases by breathing them in or through contact with skin/eyes
• Heath effects include deadly exposure, difficulty breathing and itchy skin
• Cannot be seen and can pond in depressions around active volcanoes (due to being less dense)
• Sulfur gases convert to sulfate aerosols which cause climate change when they reach the stratosphere

Question 11

What are lava flows?

Answer 11

• Flows of magma extruded onto the surface of a volcano
• Viscosity of lava flows increases with silica content and decreases with higher temperatures and water content
• Lava domes are when high viscosity lava slowly erupts and builds up

Question 12

What are the different types of lava?

Answer 12

• Most common is low viscosity, iron/magnesium rich basalts
• Temperatures of 1100 to 1200°C
• Can flow long distances
• High viscosity, silicon rich andesites are less fluid
• Erupt at temperatures of 700 to 900°C
• Form short, thick flows

Question 13

How are lava flows and lava domes a hazard?

Answer 13

• Destroys everything in its path through burial, crushing and heat
• Flows slowly so usually doesn’t cause direct loss of life
• There is sufficient time to evacuate
• Lava domes are unstable and can collapse
• This causes pyroclastic density currents

Question 14

How are pyroclastic flows a hazard?

Answer 14

• Hot density currents consisting of mixtures of rock debris and gas
• Flow along the ground at high speeds
• Travel under gravity they move downhill but can move uphill
• Temperatures range from 100 to 600°C
• Typically travel at +110km/h

Question 15

How are landslides and debris avalanches a hazard?

Answer 15

• Triggered as a result of volcanic explosions or dome collapses
• Particularly common where heavy rainfall is common
• Channelled into valleys and travel large distances beyound source
• Occur without warning and even on dormant volcanoes
• Travel at high speeds which makes it impossible to evacuate

Question 16

How are lahars a hazard?

Answer 16

• Volcanic mudflow made up of volcanic debris and hot/cold water
• Move at speeds from 10km/h to 100km/h
• A result of eruptions involving ice or snow, generating meltwater, or triggered/mobilised by heavy rainfall
• Gather more loose material as they move
• Viscous mudflows contain over 60% sediment
• Less viscous mudflows have a high water content so resemble torrential floods
  E.g. Nevado del Ruiz

Question 17

How are GLOFs/jokulhlaups a hazard?

Answer 17

• A glacial outburst flood which is a sudden release of water from a lake lying under or clsoe to a glacier
• Triggered by the eruption of a volcano underneath a glacier
• Melts overlying ice or weakens a dam made of glacial moraine sediments
• Releases huge volumes of water that wash away roads and bridges

Question 18

How are tsunamis a hazard?

Answer 18

• Water is displaced
• Caused by submarine explosions, collapse of part of a volcanic edifice, entrance of lahars or pyroclastic flows into water
  E.g. Krakatau killed 36000 people